chemistry 120 laboratory - birmingham southern collegechemistry 120 laboratory ... october 9...

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Chemistry 120 Laboratory

CH 120 Lab Schedule Fall 2012

Module 1: Density and Measurement September 4 Sink or Float: A study of bowling balls and eggs September 11 Coke vs. Diet Coke September 18 Determination of Sugar Content in Sodas using Density September 25 Molecular Modeling

Module 2: Titrations October 2 Determination of Acidity of Vinegars October 9 Neutralizing Power of Antacids October 16 Prep for Leaf Lab / Journal Club October 23 Decomposition of Tree Leaves

Module 3: Calorimetry October 30 Introduction to Calorimetry November 6 The Acidity of Vinegar – Leaf Lab paper due at beginning of class November 13 What Properties Make a Good Fuel? November 20 Group Work on Poster November 27 Poster Presentations – Electronic submission due on Moodle December 4 Kinetics

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Laboratory experiments may not be made up after your assigned lab period. If you have an excused absence (such as participation in a college sports event) you must make arrangements with your laboratory instructor in advance of the lab you will be missing. If you are ill and feel that you cannot attend lab, you must email your lab instructor before the beginning of the lab period and obtain a doctor’s excuse before you will be able to make up the experiment. Any unexcused late lab reports will have significant points deducted.

Many experiments have a pre-lab assignment that will be checked at the beginning of the laboratory period. It is important that you have read the appropriate sections of your lab manual and prepared your lab notebook prior to coming to class. Grading Your lab grade constitutes 20% of your grade in General Chemistry. A neat, legible notebook is a critical aspect of laboratory work. Your work must be legible not only to yourself but to others who may depend on its contents. Each lab, students will turn in the yellow copy pages from your lab notebook for grading along with any graphs or tables you made on the computer. These are due at the end of lab unless you have permission from your instructor to turn them in at a later time. Late papers and reports will lose 25% credit for every day late. The following is an estimation of the breakdown for points in the course and is subject to change. Notebooks/Prelabs (20 points each) 220 points Journal Club Activity (30 points) 30 points Module projects (100 points each) 300 points Total Lab Points 550 points

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BIRMINGHAM SOUTHERN COLLEGE DEPARTMENT OF CHEMISTRY AND PHYSICS

LABORATORY SAFETY AGREEMENT

Student’s copy At all times, while working in or visiting the chemistry laboratory, I will practice the following safety precautions: 1. Know the exact location of all safety equipment. 2. Never work in the laboratory alone without the knowledge of a member of the chemistry faculty

or a qualified TA. A member of the faculty must be present in the department whenever students are in the laboratory.

3. Do only the assigned experiments, following the designated procedure. 4. Wear departmentally approved eye protection at all times. Departmentally approved eye

protection is stamped with the code "Z87.1-1987" and may be purchased from the bookstore or will be provided in the form of safety goggles. Eyeglasses do not qualify as departmentally approved safety glasses.

5. Wear sensible clothing as it may be subjected to spills that will stain or burn the clothing. Also,

sandals, perforated, or open-toes do not provide adequate protection from spills. Confine long hair.

6. Keep the laboratory bench free of items not related to the experiment as they may be subject to

damage, or may increase the likelihood of an accident. 7. There will be no eating or drinking whatsoever in the laboratory. Also, be aware that anything

comes into contact with your mouth or eyes (such as fingers) may be contaminated with laboratory chemicals.

8. Dispose of waste materials as directed by your instructor. If unsure whether it is safe to dispose

of something in the sink, ask. 9. Use the fume hood when the experiment involves noxious vapors. 10. Do not use mouth suction when pipetting or starting a siphon. 11. Be aware that any object you touch may be hot. 12. Read the label on the bottle or container to be certain that it contains the desired chemical. 13. Clean the work area before leaving the lab every day. Spills or traces of chemicals left on a

bench top pose a risk to the next student that uses that work area. 14. No horseplay in the lab. 15. Report all accidents that result in injury, no matter how minor, to the instructor immediately. 16. Consult a physician if you are pregnant or have any other medical condition that might render you

susceptible to exposure to the chemicals used in this laboratory.

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I have read the safety precautions on the front of this page and understand their importance for the safety of others and myself in the laboratory. Course and Lab Section _____________ Signature __________________________ Date _____________

__________________________ (Print)

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BIRMINGHAM SOUTHERN COLLEGE DEPARTMENT OF CHEMISTRY AND PHYSICS

LABORATORY SAFETY AGREEMENT

Instructor’s copy At all times, while working in or visiting the chemistry laboratory, I will practice the following safety precautions: 1. Know the exact location of all safety equipment. 2. Never work in the laboratory alone without the knowledge of a member of the chemistry faculty

or a qualified TA. A member of the faculty must be present in the department whenever students are in the laboratory.

3. Do only the assigned experiments, following the designated procedure. 4. Wear departmentally approved eye protection at all times. Departmentally approved eye

protection is stamped with the code "Z87.1-1987" and may be purchased from the bookstore or will be provided in the form of safety goggles. Eyeglasses do not qualify as departmentally approved safety glasses.

5. Wear sensible clothing as it may be subjected to spills that will stain or burn the clothing. Also,

sandals, perforated, or open-toes do not provide adequate protection from spills. Confine long hair.

6. Keep the laboratory bench free of items not related to the experiment as they may be subject to

damage, or may increase the likelihood of an accident. 7. There will be no eating or drinking whatsoever in the laboratory. Also, be aware that anything

comes into contact with your mouth or eyes (such as fingers) may be contaminated with laboratory chemicals.

8. Dispose of waste materials as directed by your instructor. If unsure whether it is safe to dispose

of something in the sink, ask. 9. Use the fume hood when the experiment involves noxious vapors. 10. Do not use mouth suction when pipetting or starting a siphon. 11. Be aware that any object you touch may be hot. 12. Read the label on the bottle or container to be certain that it contains the desired chemical. 13. Clean the work area before leaving the lab every day. Spills or traces of chemicals left on a

bench top pose a risk to the next student that uses that work area. 14. No horseplay in the lab. 15. Report all accidents that result in injury, no matter how minor, to the instructor immediately. 16. Consult a physician if you are pregnant or have any other medical condition that might render you

susceptible to exposure to the chemicals used in this laboratory.

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I have read the safety precautions on the front of this page and understand their importance for the safety of others and myself in the laboratory. Course and Lab Section _____________ Signature __________________________ Date _____________

__________________________ (Print)

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CH 120 Guidelines for Laboratory Notebooks

For this class, you will need a carbonless duplicate copy laboratory notebook that can be purchased in the bookstore. You will need to bring this to lab each week and if you do not have it, your lab score will be lowered by 25% that week. It is not acceptable to do your work on paper and then transfer it to your lab notebook after class. All laboratory work must be recorded in your notebook. These lab notebooks make carbonless copies of your work. Selected students will be required to turn in the copy at the end of each class period. Follow the guidelines listed below for your lab notebook:

Ø Be sure to use the cardboard cover under the page while you are writing in your notebook. If you forget, you will ruin the copy pages for future work.

Ø Never tear out a page in your laboratory notebook. The pages are numbered and if pages are missing you will lose points. If you make a mistake, you simply cross through your work and begin again.

Ø Do your work in pen (no lead pencil) so that you get a clean copy. The copy is what will be graded; so be sure it is clear and readable. If you make a mistake simply cross it out neatly with a single line through the error.

Ø Each week update the table of contents in the front of the lab notebook. Ø When you have tables or graphs that are made using a computer, be sure to save a copy to

a portable digital memory device (ie, flash drive) with the folder location and document title written in your notebook. Make a hard copy to turn in with your carbon copies.

Each week your laboratory notebook will have the following format: Heading: Title, Date, Name of lab partner(s). Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to give

enough details that someone reading it can repeat your procedure. If you prepare this section before doing the experiment, leave enough room to make modifications if needed.

Data: Typically this section will consist of tables of experimental data you collect. Be sure all

data is labeled with proper units and recorded to proper accuracy. Calculations and Results: Show your calculations. Be sure to give any formulas you used and

clearly define the variables. All calculations should include proper units. Be sure to calculate the standard deviation of all repeated measurements. All final results should be circled and have the proper units. You should include the results of your work and any accumulated results of the class. These will often be in the form of a spreadsheet, graph or table.

Conclusions: Summarize any conclusions in complete sentences. Most weeks you will also

have questions to answer for this section. Answer in complete sentences so that someone could understand the answer without reading the question.

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General Chemistry Equipment List

Beaker Erlenmeyer Flask Wash Bottle Funnel

Graduated Cylinder Buret Electronic Balance Stirrer/Hot Plate

Evaporating Dish Volumetric Flask Thermometer Pipet

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Watch Glass Crucible Tongs

Wire Test Tube Clamp Dropper Bottle Glass Stirring Rod Spatula

Stir Bars Test Tube Brush Red and Blue Litmus Paper

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CH 120 Laboratory Module 1 Density and Measurement

Week 1: Sink or Float: A Study of Bowling Balls and Eggs Week 2: Coke vs. Diet Coke Week 3: Determination of Sugar Content in Sodas Using Density Skills for this module: In this module you will perform a variety of measurements and draw conclusions based on the resulting data. In the process you will learn the following techniques: 1. Determination of volume using a graduated cylinder, a pipet and a buret. 2. Using standard deviation to determine precision of measurements. 3. Using a spreadsheet to graph data and perform calculations. 4. Using a standard curve for determining an unknown value. Outcomes: By the end of the module you should have: 1. Determined the relationship between mass and volume of an object. 2. Determined the relative accuracy and precision of a variety of glassware. 3. Determined the relative density of Coke vs. Diet Coke. 4. Determined the sugar content of a variety of drinks using a standard curve. Final Product: At the end of this module, you will submit a modified lab report that describes the results you obtained in Weeks 2 and 3, as well as a discussion of them. See page 29 for more details on this assignment. You will record your data in table-form in your notebook, and you will create graphs with your data using Excel. Each table/graph should include: Table Graph (i) Title (i) Title (ii) Column Headings (ii) Axes labels (iii) Caption (iii) Caption (iv) Author (iv) Author (v) Lab partner (v) Lab partner (vi) Date (vi) Date

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Week 1: Sink or Float? Objective: In this week’s experiment we are going to investigate factors which determine whether an object sinks or floats. Part 1 Will the bowling ball sink or float1?

Bowling balls are rather complicated objects. The outer shell of the ball is made of polyester or polyurethane while the inner core is made of a composite material that is usually proprietary. The core of the ball has a block made of denser material to compensate for the loss of mass due to the drilling of holes. Depending on the positioning of the denser material, the ball may rotate differently causing it to hook. You and your lab group will be assigned a bowling ball. You will be provided scales, string and rulers. Use these items to design a procedure and collect data to determine whether your ball will sink or float in tap water. You must do this without actually putting the bowling ball in water. Once all group members have written up a procedure in their lab notebook, you should have it approved by your instructor before proceeding. You can request additional materials from your instructor if needed. Each measurement should be performed independently by each group member and all group values (class data) recorded in the data section of your lab notebook. You will test your prediction by placing your bowling ball in water at the end of class.

WARNING: Bowling balls are heavy and can easily roll. Do not place your bowling ball on the lab bench without securing it or it could roll on to the floor.

Lab notebook instructions for Part 1: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your measurements. Be sure you have enough detail that someone reading it could repeat your procedure. Data: Record the measured data that you and your group members collect on your bowling ball. You should do several trials to confirm your measured values. All data should be in proper units and significant digits. Calculations and Results: Show your calculations. Be sure to give any formulas you used and clearly define the variables. All calculations should include proper units and significant digits with final values circled. Based on your calculations, what do you predict will happen? Record your actual result in your lab notebook. A class data table should include the final results determined by all of the groups in the class. Conclusions: Based on the class results, what general conclusions can you draw from this experiment? List at least four.

1 Adapted from Holley, K.; Mason, D.; Hunter, K. J. Chem. Educ. 2004, 81, 9, 1312

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Part 2 The Floating Egg2 You and your group will need to determine the density of a salt solution required to just float an egg. This means the top of the egg will touch the top of the solution without any significant portion of the egg protruding from the surface. At this point, the density of the egg is equal to the density of the solution. To measure volume you will use a graduated cylinder. Be sure to carefully look at the markings on the cylinder. The liquid in the cylinder will dip slightly towards the center forming a meniscus. You should measure the volume from the bottom of this meniscus. Note that the last value you record will be estimated between the graduated markings. Be sure you record all measurements to the proper accuracy in your lab notebook. To measure the mass you will use an electronic balance. This is a very delicate (and expensive) piece of equipment that needs to be treated with care. You will use weigh boats to hold the chemicals you are massing. Do not add chemicals to the weigh boats while they are on the balance. If you need to add more of a substance, first remove the weigh boats from the balance before adding. If you do spill some chemicals on the balance, please contact your lab instructor or TA immediately so that it can be cleaned up. Even simple table salt can corrode the balance if left there for any significant period of time. Plan your experiment with your lab group. Seek approval from your instructor before beginning. Record your final values in the class data Excel spreadsheet table on the computer. Calculate the standard deviation of the class data (see skill box below). Skill Box Calculating Standard Deviation When you have a set of data, one important piece of information is the precision of the measurements. The precision tells you how large the deviation of the data is from the average value. To report the precision of your data you need to determine the standard deviation. a. First determine the average or mean, X , of your data set. Add your values and divide by the

number of measurements. b. Then find the deviation for each measured value by subtracting the mean from each value. c. Square each of the deviation values (this gets rid of any negative signs) and add them up. d. Take the value from Part c. and divide by the total number of measurements minus 1. Then

take the square root of this value. This is your standard deviation. Most calculators have a standard deviation function that you can use, but you should understand what that calculation is doing.

2 Adapted from Wink, D. J.; Gislason, S. F.; Kuehn, J. E. Working with Chemistry; A Laboratory Inquiry Program; W. H. Freeman and Company: New York, 1999.

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Example: Data Deviations (Deviation)2 12.11 12.11 - 12.14 = -0.03 (-0.03)2 = 0.0009 12.15 12.15 - 12.14 = 0.01 (0.01)2 = 0.0001 12.12 12.12 - 12.14 = -0.02 (-0.02)2 = 0.0004 12.17 12.17 - 12.14 = 0 03 (0.03)2 = 0.0009 12.14 12.14 - 12.14 = 0 00 (0.00)2 = 0.0000 60.69 0.0023

60.69/5 X = 12.14 This measurement would be reported as 12.14 + 0.024 (the 0.004 is not significant but one extra figure is usually carried for statistical purposes). The standard deviation is a quantitative measure of the spread of the data. Lab notebook for Part 2: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to have

enough detail that someone reading it could repeat your procedure. Data: Record the measured data that you collect on your solution. Be sure all measured values

are given to the proper accuracy and have units. Calculations and Results: Show your calculations. Be sure to give any formulas you used and

clearly define variables. All calculations should include proper units and significant digits and your final values circled. Record the density of your egg in your lab notebook. Include a data table of the class results. Calculate the mean and standard deviation of the class density values.

Conclusions:

a. Quantify (compare) numerically the differences between your data and that of the class. Explain any differences you may observe.

b. Would you conclude the variation in the data is due more to differences between the

individual eggs or differences in the measurements done by the class members? Explain. c. Which of the two measurements, mass or volume, limits the accuracy of your final value?

Explain your answer.

0240400230 ..

=

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Prelab for Week 1: 1. Given the following data, calculate an average and standard deviation for the data set: Sample # Absorbance 1 0.488 2 0.480 3 0.486 4 0.473 Average= ________ 5 0.475 Std Dev = ________ 6 0.482 7 0.486 8 0.482 9 0.481 10 0.490 Show your calculations on the back of this page. 2. The following is a plot of the above data with the average shown as a straight line

through the data. Based on your calculation for the standard deviation of the data set, do all the values fall within:

(i) one standard deviation of the average? (ii) two standard deviations of the average?

0.400

0.450

0.500

0.550

0.600

0.00 2.00 4.00 6.00 8.00 10.00 12.00

Absorbance (unitless)

Sample Number

Sample Data for Prelab 1

Absorbance Average

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Week 2: Coke vs. Diet Coke3 Objective: In this experiment you will determine the densities of Coke, Diet Coke, and water. You will also determine how the density varies with sample size. Prelab: Before coming to lab you should read over the lab materials and prepare a procedure and data tables in your notebook. Be sure to leave space for making additions or corrections to your procedure. Part 1: Are the densities of Coke and Diet Coke different? You and your group will be given a sample of degassed Coke and Diet Coke. You will determine the volume of the two samples using three different types of glassware: a pipet, a buret, and a graduated cylinder. Your instructor will demonstrate how to use each piece of glassware. The masses of the beverages will be measured using an electronic balance. Be sure to record all measured values to the proper number of significant digits. Each student should measure out 25 mL of Coke or Diet Coke using each piece of glassware giving a total of 3 samples per student and 6 samples per group. You may want to practice using the pipet several times with water before doing your measurements on the soda samples. Your data table for Part 1 should include columns for recording the mass of the empty beaker, mass of beaker and soda, mass of soda, and volume of soda for each sample you measure. Your group should prepare an Excel spreadsheet that will calculate the densities of each sample from the measured mass and volume. Be sure to designate which piece of glassware was used to measure volume in each case. Add your group data to the class database where the data will be plotted. From the class data calculate the mean and standard deviation for the density based on each type of glassware. Which type of glassware is the most precise? List in your lab notebook any observations and conclusions you can draw from the class data. Laboratory notebook outline for Part 1: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your measurements. For this part of the lab, this will not be too long. Data: Make a data table for the mass, volume, and density of each of your samples using each piece of glassware. Record data with proper number of significant digits and units. Calculations and Results: All calculations should include proper units with final values circled. Be sure to calculate mean and standard deviation of the class values. Include a 3 Adapted from Herrick, R. S.; Nestor, L. P., Benedetto, D. A. J. Chem. Educ. 1999, 76, 10, 1411

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spreadsheet for your group’s data and the plot and spreadsheet for the entire class data. Graphs and tables must include a meaningful title and the graph must have axes labeled with units. One copy of the tables and graph should be stapled to your notebook and another turned in with your carbon copies. Conclusions: a. Quantify (compare) numerically the differences between your data and that of the class.

Explain any differences you may observe. b. Which type of glassware give the most precise values for volume? How did you determine

this? c. Is this glassware the most appropriate to use in all experiments? Why or why not? d. Is it possible for a measuring device to be precise but not accurate? Explain. Part 2: Does density vary with sample size? Each group needs to determine the density of Coke, Diet Coke, or tap water using a variety of different sample sizes. You need to collect at least eight (four per student) different data points at a variety of volumes for your assigned liquid. Which glassware should be used to measure volume? Decide as a group how you will collect the data. Record the data you collect in your lab notebook and make a spreadsheet including all the data for your group. Calculate the average and standard deviation of your group data. Be sure to record all measured and calculated values using the correct number of significant digits. As a group you need to decide the best way to graph the data to present your results. You need to show how the mass varies with sample volume. When making graphs, the variable that you control in the experiment is call the independent variable and should be graphed on the X-axis. The measured variable that results from your independent variable is called the dependent variable and is plotted on the Y-axis. You should fit your data to a trendline. Record your average density value and standard deviation on the class data table to compare your values with those obtained by other groups. What conclusions can you draw about the densities of Coke, Diet Coke, and water? Attempt to explain these results.

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Clean Up All solutions can go down the sink. Be sure to rinse your glassware well with distilled water (faucet with white handle). Do not remove burets from stand but instead rinse them with squirt bottles. Store them upside down on the stand with stopcock opened. Laboratory notebook outline for Part 2: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your measurements. For this part this

will not be too long. Data: Make a data table for the mass, volume, and density of each of your samples in your lab

notebook. Report the average and standard deviation for your data. Include all data from your group on a spreadsheet. Be sure all data has units.

Calculations and Results: All calculations should include proper units. For any multiple

measurements, you should calculate the average and standard deviation. Include a plot for your group’s data. Graphs must include a meaningful title and the axes must be labeled with units. A copy of the plot should saved and one hard copy per group turned in with your carbon copies. For each type of liquid give the class mean (averaged value) with the standard deviation.

Plot your data using Excel to show the effect of sample size on density. Include a copy of the plot with the yellow copy of your “Conclusions” answers. Conclusions:

a. Quantify (compare) numerically the differences between your data and that of the class. Explain any differences you may observe.

b. Which beverage is the most dense? Give possible explanations for this.

c. Does the density of a substance depend on the sample size? Explain based on your data.

d. What is the density of your beverage based on your graphical analysis? Compare your

averaged density value with the value from your graph?

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Week 3: Determination of Sugar Content in Commercial Beverages4

Objective: In this experiment you will use density to estimate the sugar content in a variety of commercial beverages. By comparing your values to those given on the label, you will determine how accurate your estimates are. Pre lab assignment This week you will be using density to determine the amount of sugar in commercial beverages. Before lab you will need to do the following: 1. Write up a procedure to make your standard sugar solutions. You will need 4 solutions in the

range of 4.0 – 18% sugar by mass using 50 mL of water. You will be provided with 10- and 25-mL pipets, a buret and the glassware in your drawers. Calculate the specific amount of sugar you will use in each sample and show your work. Record this information and calculations in your lab notebook. You may assume that the water you use to make up the solution has a density of 1.00 g/mL.

Mass % = 100 water)(sugar solution of mass total

(sugar) solute mass×

+%

2. Answer the following prelab question on a single page of your notebook. Make a pre lab

question section in your notebook after your procedure and be sure to show all work including any equations or conversion factors you use. For this problem you will need to use a value that was determined in the previous week’s experiment.

A 12.0 fl. oz. can of Coke contains 39.0 grams of sugar. Assuming that sugar and water make up the vast majority of the mass, what is the mass % of sugar in Coke? Note that a fluid oz is a unit of volume and is not the same as an ounce used to measure mass. 3. Bring in a commercial beverage in which sugar is the primary ingredient. This can be a soda,

sports drink, or fruit juice (without pulp). The second ingredient (after water) should be high fructose corn syrup or sucrose. A 12-oz can or 20-oz bottle should be sufficient.

4. Before coming to lab prepare data tables in your laboratory notebook.

5. Find, and write in your notebook, a definition for the scientific term “aliquot”. In class Discuss your approach for making up your standard sugar solutions with the class at the beginning of lab. You will then begin making up your solutions. Be sure all of the sugar is dissolved before doing any measurements. For each standard solution you will need to

4 Adapted from Henderson, S. K.; Fenn, C. A.; Domijam, J. D. J. Chem Educ. 75, 9, 1122.

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determine the density of three separate aliquots of the solution. Discuss with your group the best way to do this. Your group may use a spreadsheet for your data. Prepare your standard curve and do a linear fit (trendline) of the data (see page 34 as an example). Your group will present the results of your standard curve to the class. After each group has presented their standard curve results, each student will measure the density of a commercial beverage. You may use the drinks you brought to class or the ones provided in the lab. Be sure your group tests a variety of different beverages, but it is also a good idea for two students in the class to independently test the same beverage. If you are testing a carbonated drink, you will need to degas it by stirring it on a stir plate until the bubbles are gone. Use a beaker or flask and cover it with a watch glass. This should take about 20 minutes. For each beverage you test, you need to do at least 3 density determinations and calculate an average value and standard deviation. Use the linear fit from your standard curve to determine the mass % sugar for each beverage. From your experimental results, you also need to calculate the grams of sugar per serving. The serving size is given on the label. In your notebook you should also record the label value for grams of sugar per serving for comparison. Record your results for your commercial beverages (density, mass% sugar, grams of sugar, label value) on a class spreadsheet. You should record the entire class results in your laboratory notebook. Also record any conclusions you can make for the data. As a class, discuss the results and conclusions. Are there any trends in the data? Compare your experimental results to the sugar values given in the nutritional information and calculate a % error value. Is this method effective in determining the sugar content of the beverages? Why or why not? What assumptions are you making in this experiment?

%100Value Actual

Value Actual -Value alExperiment Error Percent ×=

Outline of Experiment

I. Prepare standard sugar curve A. Make up sugar solutions using pre-lab calculations (4 per group) B. Determine density of standards (3 determinations per sugar solution) C. Calculate linear fit of data (include trendline and R2 value)

II. Determination of sugar content in beverages

A. Degas beverage if carbonated B. Determine density of beverage solutions (3 determinations) C. Using linear equation from the standard curve, determine mass % sugar D. Calculate grams of sugar per serving E. Calculate % error from label value

III. From class data determine the trends in sugar content of beverages

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Laboratory notebook outline for Week 3: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your work. The procedure for preparing

standard solutions should be completed before class followed by the pre-lab question. Data: Make a data table for the mass, volume, and density of each of the standards measured by

your group and the beverage you independently measured. Include your results in a class spreadsheet showing the final densities, mass % sugar, and grams of sugar for the commercial beverages. All data should have units and be recorded to the proper number of significant digits.

Calculations and Results: Show your calculations. Be sure to give any formulas you used and

clearly define the variables. All calculations should include proper units with final values circled. Include the graph for your group’s data for the standard curve with the linear fit. Graphs must include a meaningful title and the axes must be labeled with units. A copy of the plot should be saved and one hard copy per group turned in with your carbon copies.

Conclusions: Answer the following in complete sentences:

a. Which drinks had the highest sugar content? Is there a particular category of drink (sodas,

sports drinks, juices, etc) that are higher in sugar content? b. How did your experimental results compare to the sugar content given on the label (be

specific, do not just say they were close)? Explain any differences. c. Was the method used for determining sugar content effective? What approximations do

you make using this procedure? Explain why these approximations are reasonable or not. d. If you did not degas a soda before doing your measurements, do you think the amount of

sugar would have been too high or too low? Explain your answer.

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Example of Graph Format with a Trendline

Appropriate Title for Graph (do not use axes labels)

y = 0.0042x + 0.9926R2 = 0.9892

1.00

1.01

1.02

1.03

1.04

1.05

1.06

1.07

1.08

3 5 7 9 11 13 15 17 19 21

Mass % Sugar

Den

sity

, g/m

L

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Module 1 Date: ______ Week 3 Report Sheet Determination of Sugar Content in Commercial Beverages Name: ______________________ Lab Partners: _________________ _________________ Part 1: Standard Curve Mass % Sugar Average Density (with standard deviation) Plot your data using Excel to produce a calibration curve of Density vs Mass % Sugar. Include an appropriate title, axes labels, and trendline. Include the fit equation with R2

value on the plot. Attach a copy of your plot with this report.

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Part 2: Commercial Beverage Sample: ____________________ Mass % Sugar (from graph)

Grams Sugar per Serving (measured)

Grams Sugar per Serving (Label)

% Error

Average Grams Sugar per Serving (Measured): __________________±_______ Conclusions: Attach the yellow copy of your notebook including the “Conclusions” answers to this worksheet.

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CH 120 Laboratory Module 1 Density and Measurement: Results/Discussion Assignment

At the end of Module 1, you will electronically submit a laboratory report detailing your results and a discussion of them from weeks 2 and 3 of this module. The format is as follows:

Results and Observations: This should give the results of your experiments and not be a discussion of why they occurred. For the investigations you did, you should detail your results and any observations or problems you encountered. Any tables or graphs should have a meaningful title or caption and be clearly labeled (see examples under “Notes”). The reader should be able to independently read the table or graph and get all the information needed without having to read the laboratory report. The results section of your report should not simply be a list of graphs and tables; it should include text that describes what is shown.

There are several specific results you should be sure to include in this portion of your paper:

Week 2, Part 1:

• A table of your group’s data showing the densities of Coke/Diet Coke using a graduated cylinder, pipet, and buret; data should be in proper number of sig. figs. and correct units. Should include an average density and standard deviation for each piece of glassware.

• Graph from class data showing the density of Coke vs. Diet Coke using different glassware

Week 2, Part 2:

• Table showing the volume, mass, and density of Coke, Diet Coke, or water from your group data. You should also include the average density and standard deviation.

• Scatter plot of the mass vs. volume of your group’s beverage (Coke/Diet Coke/water). Make sure you include a trend line, the trend line’s equation, and its R2 value.

Week 3:

• Graph showing the average density vs. the mass % sugar for your standards. Make sure you include a trendline, the trendline’s equation, and its R2 value.

• Class data table showing calculated values of the different commercial beverages you all studied. **In the text, be sure to highlight the specific values from your group!

Hint: You’ve already created most of these tables and graphs in lab! Just be sure that they are formatted and labeled/captioned properly. (Again, see “Notes.”) Make sure you include correct units and sig. figs. for your values!

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Discussion In this section you will discuss your results. How did your experimental values compare to the expected values? How did the results compare between different class members? What might account for these differences (do not just say human error). In addition, describe how you used the results from each week to design your protocols. Be as specific as possible about any assumptions you have made in your analysis of results and how they might affect your outcome. Your discussion should be in paragraph form.

Hint: Go back and look through your answers to the Conclusion questions from the end of each week. Incorporate the answers to these questions into your discussion of your results.

Notes:

• Students should review the definition of plagiarism in the BSC Honor Code. If you are uncertain, ask for help at the writing center or from your instructor. Ignorance is not an excuse.

• All tables included in your report should be numbered (i.e. Table 1) and have a meaningful title shown above the table. For example:

Table 4: Spectrophotometer Readings Water, Epicatechin, and Tea Samples at 750 nm

Sample Tested Absorbance

Water 0.0320

Epicatechin (50 µM) 0.2067




5% Tea 0.1583

10% Tea 0.3148

20% Tea 0.5449

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• Graphs and figures should not be titled at the top, but they should include a detailed caption below. The caption should also include a figure number that follows in succession with the others in your paper..

Figure 2. The percent inhibition versus the concentration of Trolox in a 25 mL sample of Lipton black tea. Each tea sample was measured in duplicate.

• Equations or reactions should be indicated with a number in parenthesis on the right side:

ΔAABTS·+ = A735Control - A735Test (1)

• All tables, graphs, and figures should be referred to in the body of the paper and should

not be broken by a page break. The reader should be able to independently read the table or graph and get all the information needed without having to read the laboratory report.

• References should be presented in American Chemical Society format. You may use either endnotes or footnotes but indicate where the reference goes using a superscript in the text1. Be very careful in using sources from the web. All sources should be reviewed (a scientific journal), from an edited publication (such as a textbook, Time magazine, or Scientific American), or a government website (such as Environmental Protection Agency or Food and Drug Administration). Wikipedia is not an appropriate reference for a formal lab report. Also, your BSC lab manual is NOT a reference.

0% 10% 20% 30% 40% 50% 60% 70%

0 50 100 150 200 250 300

Perc

ent I

nhib

ition

Concentration Trolox (µM)

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Ø Books:

Author (Last name, Intials; separate with semicolon if more than 1). Title (in italics); Publisher: City, year; p. #. Example: 1 Anthony, S; Brauch, T. W.; Longley, E. J. What Should We Do About Global Warming?; Wiley: New York, 1998; pp. 150-153.

Ø Journal:

Author (same as above). Journal name(abbreviated and in italics). Year (bold), volume, page. Example: 2 Porter, D. J.; Stewart, A. T.; Wigal, C. T. J. Chem. Educ. 1995, 72, 1039.

Ø Web:

Author (if any). Title of Site. URL (accessed Month Day, Year), other identifying information (if any). Example: 3 International Union of Pure and Applied Chemistry Home Page. http://www. iupac.org/dhtml_home.html (accessed April 24, 2005).

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CH 120 Laboratory Week 4: Molecular Modeling Objective: In this exercise you will use ball and stick models and the computer modeling program Spartan to determine the shape and properties of a variety of compounds and ions. Part I: Ball and Stick Models: When determining the shape of a molecule you must go through the following steps:

A. Draw the Lewis Structure minimizing formal charge.

B. Determine the number of electronic groups around the central atom. An electronic group may be a bond (single, double or triple), a lone pair of electrons, or a single unpaired electron.

C. Determine the Electron Group Geometry from the number of electronic groups.

Number of electron groups Electron Group Geometry 2 Linear 3 Trigonal Planar 4 Tetrahedral 5 Trigonal Bipyramidal 6 Octahedral

D. Determine the shape by looking at the number of bonding and non-bond groups. [See Figure 10.10 on page 379 of your textbook.]

Pre-lab assignment: In class you will be building models for the compounds and ions listed in Table 1. Before lab, complete the second column (Lewis Structure) of the table by drawing the Lewis structure for each compound or ion. Be sure to use the concept of formal charge to find the best Lewis structure for each compound or ion. Some compounds may violate the octet rule when it is appropriate.

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Table 1. Shapes of compounds Skeleton Structure Lewis Structure 2-D Projection or Wedge

Structure Name of Molecular Geometry (shape)

* CO2

O3

H2O

* NO3

-

SCN-

NH3

SF6

* XeF4

BrF3

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In Class: Part A. Simple Molecular Structures Using the Lewis structures you drew in the Pre-Lab assignment, build a model for each of the starred compounds or ions in Table 1. Be sure you are using a ball for the central atom with the correct number of holes for your electron group geometry. You should have an empty hole for each lone pair. For multiple bonds you can use the longer more flexible bonds that can bend to make a double or triple bond. Your TA or instructor can demonstrate this for you. After you have built the model, represent its 3-D structure in the next column using a 2-D projection or wedge structure. The tetrahedral molecule CH4 is drawn below as an example. The tetrahedral shape is three-dimensional. The shape can be drawn by a projection into two dimensions. We will use a wedge to indicate a bond coming out of the paper, a solid line to indicate a bond in the plane of the paper, and a dotted line to indicate a bond going into the paper. Build the model of CH4 and see if you can determine which projection of the molecule corresponds to each drawing.

Draw the 2-D projection or wedge structure of each molecule in Table 1 and give the appropriate name for its shape (molecular geometry). Part B Chains and Double Bonds There is free rotation about a single bond. Make a model of

The CH3 groups are free to rotate with respect to each other. Most of the time the ends will be staggered as shown in the three-dimensional drawing.

CHH

H

H

C

H

H HH

C

H

H HH C

H

H

HH

H C C HH H

H H

C CH

HH HH

H

36

A double bond is rigid and there is no free rotation. Make a model of

You can connect two bonds between two tetrahedral atoms, although this will bend the connectors. Since there is not free rotation about this double bond, the molecule is flat and two-dimensional. The H-C-H angle is 120°.

This means that the structures below are identical compounds

but

are different compounds. Use the models to convince yourself of these points.

H C C HH H

C CH

HH

H

C C

H

Cl

H

H

Cl

H C C

Cl

H

H

Cl

H H

C C

H

Cl

H

Cl

H H

C C

H

Cl

H

Cl

H

H

C CCl

HH

ClC C

H

ClH

Cl

and

37

Make a model of at least one of the structures below:

What seems unusual about the shape of these molecules? Draw the molecules in your laboratory notebook using the 3-D wedge structure. Part C Rings and Things Make a model of C6H12

Arrange the model so that "one end is up and the other is down" (ie., it appears as a chair). This is the preferred configuration. Notice that the ring is puckered and there are hydrogen atoms in two different environments, six pointing out from the ring and six pointing up or down from the ring. Tag the six pointing out with white labels, then push the upper end down and the lower end up and notice that the two types of hydrogen atoms interchange positions. Arrange the model so that both ends are up. This is not the preferred conformation because of the enhanced repulsive interaction between the two top hydrogen atoms. Make a model of the five-membered ring of five CH2 groups. This ring is almost flat and there is only one type of hydrogen atom. Make a model of the corresponding four-membered ring. This is flat and there is some strain in the bonds. Repeat for the three-membered ring and notice a lot of strain.

C C C

H

H

HH

H

H

H

H C C C

H

C

HH

H

H

H

H

H

H

H

and

C

CC

C

CCHH

H H

H

H

HH

H

H

HH

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Part D Isomers Section A There may be more than one way to arrange a set of atoms into a molecule. For example, the empirical formula, C4H8, has the following isomers:

Make models and convince yourself that there are five and only five isomers. Section B Make a model of C5H12. There are three different isomers of this compound. Build them using the models and draw them in your lab notebook. Be careful that you do not have any identical structures. Section C Make a model of C5H10 and draw a minimum of 6 isomers of that compound in your lab notebook. There are 12 isomers of this compound.

C C C C

H

H

H

H

H

H H

H

C C C

C

H

H

H

H

HH H

H

C C C C

H

H

H

H H H

H

H

CCCC

H

H

H H

H H

H

H

CC C

C H

H

H

H

HH

H

H

39

Part II. Molecular Modeling using Spartan '08 Your instructor and T.A. will be present to answer any questions you might have about Spartan '08. Follow the directions below to build molecules. Turn in your data sheet and answer the questions in your lab book. Once you have completed this exercise you may build more molecules on your own. The following is a view of the main window when Spartan '08 is opened:

The icons in the tool bar at the top are displayed below:

New- Opens new molecule window

Open- Opens previously saved window

Close- Closes current window without closing program

Save- Saves current window

View- Finalized molecule

Add- Allows addition of new atoms to current molecule

Remove- Removes atoms

Add Bond

Remove Bond

Minimize- Calculates most stable structure

Distance- measure length of bond between two selected atoms

Angles- measure angle between three selected atoms

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Answer all questions in your laboratory notebook. To start the program:

- Double click Spartan '08 icon on desktop - Click on the New icon, the entry model kit will appear at the right of the screen (shown at

right) 1) Build CH4

- Click the Add icon on the top toolbar. - Select the “Organic” tab on the toolbar on the right side of the

screen. - Click on the button displaying a carbon atom with four single

bonds on the entry model kit. - Click on the main screen. A carbon atom with four available

single bonds will appear. - Click the hydrogen button from the entry model kit. - Add a hydrogen atom to each of the available single bonds

(available bonds should appear yellow on the main screen) by clicking on each bond.

- Now that your molecule is built, click the Minimize icon (E) on the top toolbar to put your molecule in its most stable form.

- Click the View icon (V) to finalize your molecule. - Once finalized, look at several different representations of your

molecule by using the “Model” menu at the top of the screen and selecting from different views such as “wire,” “ball and wire,” “tube,” or “space filling,” from the dropdown menu.

- Return to “Ball and spoke” view. - Left click, hold, and drag the mouse on the main molecule

screen to rotate the molecule in three dimensions. Right click, hold, and drag the mouse to move the molecule to a different location on the screen. Choose a good clear view of your molecule.

- Now measure the hydrogen-carbon-hydrogen bond angle. This is done by first selecting the Angle icon from the top toolbar. Then, you select a hydrogen atom (by clicking directly on the atom), followed by the carbon atom, and followed by another hydrogen atom. The selection must be done in this order for correct calculation of the desired angle. The associated angle value will appear in the lower right hand corner of the Spartan ’08 screen. Record it in your notebook.

Question 1: What is the overall shape of the CH4 molecule? What is the expected bond angle for this molecule? Was the observed bond angle the same? Open a new molecule screen by clicking the Close icon (Discard) and then the New icon.

2) Build CF2Cl2 - Build this molecule in the same manner as CH4. - Use the Chlorine and Fluorine buttons from the entry model kit.

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- To erase errors, use the Remove and Remove Bond icons to remove erroneous atoms and bonds. Once the specific icon is selected, click on the molecule or bond that you wish to remove.

- Use the Minimize icon (E) to determine the most stable structure and finalize the molecule using the View icon (V).

- Determine the bond angles for this compound and record them in your notebook. There should be three unique bond angles.

Question 2. Do the bond angles vary between CH4 and CF2Cl2? Explain why they would be the same or different.

3a) Build CH3CH3

- Build this molecule in the same manner as above. - Determine the most stable structure of the molecule and finalize it. - Now measure the length of the bond between the carbon atoms. This is done by first

selecting the Distances icon from the top toolbar. Next, select both of the carbons that share the single bond. The length of the bond will appear in the lower right hand corner of the Spartan '08 screen. The length is calculated in Angstroms (Å), which is equal to 1x10-10 meters. Record this measurement in your notes.

3b) Build CH2CH2

- Build this molecule in the same manner as above. - For the double bonded structure of this molecule (H2C=CH2), you have two options:

1) Use the button depicting a carbon atom with a double bond in the entry model kit. Bind the two carbons together with the double bonds.

2) Use the single bonded carbon button to connect two carbons. Then use the Add Bond icon to connect two of the free bonds. Once the icon is selected, click the end of a free bond from each of the adjacent carbons. This will combine the bonds into one double bond.

- The double bond should be visible as two thinner cylinders between the atoms. - Add H atoms and minimize (E) your structure. - Now measure the length of the bond between the two carbon atoms. Record this value in

your notes. Question 3: What is the geometry around the carbon and how does it differ from CH4?

3c) Build CHCH

- Build this molecule in the same manner as above. - For the triple bonded structure of this molecule (HC≡CH), use the carbon atom with a triple

bond in the entry model kit. - Add H atoms and minimize your structure. - Now measure the length of the triple bond between the two carbon atoms. Record this

value in your notes. Question 4: How do the bond lengths of H3CCH3 , H2CCH2 , HCCH compare? Is there a difference between the lengths? Why, or why not?

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4a) Build C6H14 (Hexane) - Build this molecule by linking together six carbon atoms (all single bonds). - Add H atoms and minimize (E) your structure. - Rotate the structure to observe the overall shape of the molecule. Question 5: Is it linear, as it would appear on paper? Why or why not?

4b) Build C6H12 ring (Cyclohexane) - Connect six carbons together in a ring. Connect any broken bonds using the Add Bond

icon. (Unconnected bonds remain yellow. Connected bonds are gray. Make sure that all bonds in the ring are gray before proceeding.)

- Add H atoms and minimize (E) your structure. Question 6: How does this structure compare to the unminimized structure you built? - View the ring molecule in the “Space-filling” view. Question 7: Is there much room in the center of the ring?

4c) Build C6H10 (Cyclohexene)

- Connect six carbons together in a ring. - Combine two free bonds from adjacent carbons together using the Add bond icon. This

will create the needed double bond. - Add H atoms and minimize your structure.. Question 8: Is the structure of the ring planar?

5) Build C6H6 ring (Benzene)

- To make this ring (a benzene ring), connect 6 carbons using the carbon button displayed to the left. This button signifies the alternation of a double bond between two bonds on the carbon atom. This alternation is present in this type of ring.

- Make sure that all of the alternating double bonds are bound (No yellow). - Add H atoms and minimize your structure. - Measure and record the length of all the carbon to carbon bonds in the ring

Question 9: Are all of the carbon to carbon bonds in benzene the same length? How do the lengths of these bonds compare to the length of carbon to carbon single, double, and triple bonds? Why?

- View the molecule in the “Space-filling” view. Question 10: Is there much room in the center of the ring? Is the molecule planar? 6) Build CH3COCH3 (Acetone)

- Build this molecule by first selecting the carbon atom with one double bond and two single bonds.

- Now attach an oxygen atom with a double bond to the double bond of the carbon atom.

43

- Attach the two additional carbon atoms (four single bonds). - Add H atoms and minimize your structure. - Now measure the oxygen-carbon-carbon and the carbon-carbon-carbon bond angles using

the Angle icon on the top toolbar. Make sure that you select the atoms in consecutive order. Record the two calculated angles in your notebook.

Question 11: What is the overall shape of acetone (disregard the hydrogen atoms present for this question)? What is the expected bond angle for this geometry? Were the observed bond angles the same? Why, or why not?

7a) Build NF3 and calculate its dipole moment. - To build this molecule must first click on the “Inorganic” tab

on the entry model kit. The entry model kit should change to look like the image to the right.

- Use the button on the “Inorganic” tab to make the center nitrogen atom with three bonds. Make sure that the other atoms are restricted to only one bond by using the button.

- Once the molecule is built minimize the structure. - Begin the dipole moment calculation by clicking the “Setup”

menu from the top toolbar and then selecting the “Calculations…” option. This should open the Calculations window.

- Leave all of the values in their default form. - Click the “Submit” button. - Save the file as “NF3” to start the calculation. A window

should pop up, letting you know that the calculations have started. The calculation takes a few seconds, during which nothing should happen on screen. At the conclusion, another pop up window will let you know that the calculation is complete. This molecule may shift its form.

- Click on the “Display” menu from the top toolbar and select the “Properties” option. This should open the Molecule Properties window.

- Click on the box labeled “Display Dipole Vector” to show the molecule’s dipole moment on the main Spartan ’08 window. Record this value in your notebook.

Question 12: What is the overall shape of this molecule? Does it have a dipole moment? Why, or why not? - Close the molecule, and open a new window.

7b) Build BCl3 and calculate its dipole moment - You must use the “Inorganic” tab for this molecule

- Make sure that you use the boron atom and use the button to make the three bonds. Also make sure that the chlorine atoms only have one bond by using the button.

- Once the molecule is built, minimize the structure. - Calculate the dipole moment and record it in your notebook. Save the file as “BCl3” for the

calculation.

44

Question 13: What is the overall shape of this molecule? Does this molecule have a specific dipole moment? Why, or why not? - Close the molecule, and open a new window

7c) Build BrF5 and calculate its dipole moment.

- Build this molecule in the same manner as above. - Use the button on the “Inorganic” tab to make the center bromine atom with five

bonds. Make sure that the other atoms are restricted to only one bond by using the button.

- Calculate the dipole moment and record it in your notebook. Save the file as “BrF5” for the calculation.


7d) Build SiBr2F2 and calculate its dipole moment.

- Use the button on the “Inorganic” tab to make the center silicon atom with four bonds. Make sure that the other atoms are restricted to only one bond by using the button.

- Calculate the dipole moment and record it in your notebook. Save the file as “SiBr2F2” for the calculation.


7e) Build SF6 and calculate its dipole moment.

- Build this molecule in the same manner as above. - Use the button on the “Inorganic” tab to make the center sulfur atom with six bonds.

Make sure that the other atoms are restricted to only one bond by using the button. - Calculate the dipole moment and record it in your notebook. Save the file as “SF6” for the

calculation. Question 16: What is the overall shape of this molecule? Does it have a dipole moment? Why, or why not? - Close the molecule, and open a new window.

45

Sarin (Isopropylmethanefluorophosphonate) Background information Sarin, a nerve agent of the organophosphate type, was created in Germany in 1938. This nerve agent was developed for potential use as a chemical warfare agent by the Germans in WWII, though it was never actually used during that war. Sarin, which is usually in gaseous form, is “colorless, odorless, and highly toxic.” The gas is readily spread over large areas and is easily absorbed through the skin and inhaled.

The toxicity of sarin is due to its ability to competitively inhibit the function of the enzyme acetylcholinesterase. The inhibition of the enzyme function leads to a build up of acetylcholine in muscle and nerve synapses throughout the body. Exposure can create both nicotinic (i.e. twitching, cramping, weakness) and muscarinic (i.e. eye pain, vomiting, shortness of breath) problems. If the exposure to sarin is great, complete paralysis or death can occur. For more information about sarin, visit www.3dchem.com/molecules.asp?ID=25# Build Sarin using Spartan '08

- Open Spartan '08 by clicking on the icon on the desktop.

- Open a new molecule window by clicking on the New icon on the top toolbar.

- Start building your molecule by clicking on the “Inorganic” tab of the entry model kit. The entry model kit should change to look like the image to the right.

- Select the Add icon from the top tool bar. - Select the phosphorus button in the middle of the table. Once

this button is selected, click on the main molecule window to place a phosphorus atom with five single bonds in the window.

- Now, switch back to the original kit by selecting the “Organic” tab from the top of the entry model kit.

- Add the two oxygen atoms to the phosphorus by selecting the button that shows an oxygen atom with two single bonds. Do not try and make the double bond at this point.

- Now add the fluorine, carbon, and hydrogen atoms that are present. Use the carbon atoms that have only single bonds.

- The double bond between one of the oxygen atoms and the phosphorus atom can now be made by clicking the Add bond icon from the top toolbar and then selecting the free bond

46

on the oxygen and the phosphorus atom. - Determine the molecule’s most stable structure by clicking the Minimize icon on the top

toolbar. - Click the View icon to finalize the molecule. - Print the molecule in the “Ball and spoke” view. - ***Any errors can be corrected using the Remove and Remove bond icons*** Question 17: What is the shape around the center oxygen atom? What is the shape around the center phosphorous atom? Question 18: What is the shape around each carbon atom? Are they the same?

47

CH 120 Laboratory Module 3 Titrations

Week 5: Determination of Acidity of Vinegars Week 6: Neutralizing Power of Antacids Week 7: Decomposition of Tree Leaves Skills for this module: In this module you will perform a variety of measurements and draw conclusions based on the resulting data. In the process you will learn the following techniques: 1. Standardizing a basic solution using titration with KHP. 2. Determining the equivalence point of an acid/base titration. 3. Using a back titration to determine the amount of an excess reagent that is present in a

solution. 4. Using selective precipitation to separate a mixture of ions. Outcomes: By the end of the module you should have: 1. Determined the acidity of a variety of commercial vinegar solutions. 2. Determined the neutralizing power of a variety of commercial antacids. 3. Determined which cation can selectively precipitate carbonate ion from hydroxide ion. 4. Determined the % of hydroxide in an unknown mixture containing carbonate and hydroxide

ions. 5. Determined the amount of CO2 released by decaying leaves. 6. Determined the effect of nitrate on the rate of leaf decay. Final Product: At the end of this module you will turn in a typed laboratory report detailing your results from the leaf decomposition lab (Week 7). Your paper for this lab project is due at the beginning of your lab period the week of November 6. The format for your paper is located after the experimental protocol for Week 7 (page 67).

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Week 5: Determination of Acidity of Vinegars Objective: In this experiment you will be given a variety of commercial vinegar solutions and your lab group will need to find the acidity of each. One common method chemists use when they need to know the concentration of a solution is titration. Titration is the reaction of a species of unknown concentration with a species of known concentration. The reaction is run until the stoichiometric amounts of the reactants have been combined (this is the equivalence point as determined by pH measurements). In this experiment you will estimate this point in acid-base titrations by using an indicator that changes color. The point where the color change takes place is called the end point. The indicator may not change exactly at the equivalence point, but the difference is quite small if a proper indicator is used. The acidity of vinegar comes primarily from acetic acid. In this lab the acetic acid (CH3COOH) in the vinegar will be titrated with NaOH. CH3COOH + NaOH à NaCH3COO + H2O Before we can titrate the vinegar with the NaOH, the exact concentration of the NaOH must be determined in a process known as standardization with a known amount of acid. The most common acid used for standardization is potassium hydrogen phthalate (abbreviated KHP) whose structure is shown below:

KHP is a solid monoprotic acidic salt. The hydrogen bonded to the oxygen atom is the only acidic hydrogen capable of reacting with a base. Because KHP is a solid, the amount of acid use for standardizing the base can be very accurately measured.

50

Today, you will be using a program called “LoggerPro” which is used with the LabQuest Mini and a laptop. You will be collecting data relating the volume of NaOH you have added to your solution to the pH of the solution. One way to visualize this data is to graph the volumes of NaOH in solution versus the corresponding hydronium (H3O+) ion concentrations. There is a specific file that must be opened for you to be able to graph you data in this manner. It is called AcidBaseTitration.cmbl, and your instructor will inform you of its location.

As more NaOH is added to the solution, the H3O+ ion concentration will decrease due to the neutralization of the acid. When all of the acid has been neutralized, you have reached the equivalence point of the reaction. The equivalence point of a titration occurs when the number of moles of hydroxide in solution is equal to the number of hydronium ions. Locate the equivalence volume on the graph above.

51

Traditionally, titrations are graphed with pH rather than hydronium ion concentrations. For a graph showing pH vs. Volume NaOH added, you would click File → Open → Experiments → Probes & Sensors → pH Sensor → Drop Counter-pH.cmbl. Here is an example of a titration curve of this format for another reaction:

52

Prelab assignment: (Answer these questions in your notebook under a section titled Prelab Questions.)

1. You will begin your experiment by making approximately 500 mL of a 1 M NaOH solution from a more concentrated 6 M stock solution. Describe how you will make up your 1 M NaOH solution. Be sure to describe amounts of solution and the glassware you will use. Show any calculations you used. Remember that this solution will later be standardized so the concentrations do not need to be exact at this point.

2. After you make up your 1 M NaOH solution, you will standardize it with KHP.

Determine the grams of KHP you will need to measure out for this standardization titration. Assume your NaOH solution is 1.0 M and you want the equivalence point to occur after adding approximately 25 mL of NaOH to your KHP.

3. Before titrating the KHP with NaOH, you will dissolve the acid in water. How much

water do you think you should use? How will your results change if you used a different amount of water?

4. Vinegar bottles often list % acidity. This can be defined as:

%

If a vinegar solution claims to be 4.50% acidic, what is the molarity of the acetic acid in the vinegar? You can assume the density of the vinegar is 1.00 g/ml. It might be useful to begin your calculation by assuming you have 100 g of vinegar.

You should prepare your procedure and data tables in your lab notebook before coming to class. Leave room for modifying your procedure if needed. In Class

A. Preparation You will work in groups of two. Begin by making up the 1 M NaOH using the procedure you gave in the pre-lab assignment. Next, calculate the number of grams of KHP necessary to standardize your NaOH. Weigh out two samples of the proper amount of KHP and transfer them to separate beakers. If you do not exactly weigh out the amounts you determined in the pre-lab, do not be concerned, but record the masses for each sample in your lab notebook. Dissolve your KHP samples in deionized water and add 3-4 drops of phenolphthalein indicator to them. Next, fill the plastic reservoir with NaOH, place a waste beaker under its spout, and adjust its stopcocks.

53

Skill Box: How to Adjust Double Stopcocks Turn both nozzles vertically. Solution should be flowing freely through the spout. Adjust the top nozzle so that drops are released from the spout at a rate of about one drop per second. The bottom nozzle should serve only as an on/off switch. The vertical position will allow drops to flow at the speed you set with the top nozzle; the horizontal position will stop them. The pH sensor should be connected to “CH1” and the drop counter to “DIG1.” To calibrate the drop counter, click “Experiment,” “Set Up Sensors,” and “Show All Interfaces.” Click the Drop Counter and select “Calibrate.” Here, enter a drops/mL ratio given by your instructor. Place your first KHP sample on top of the stir plate and underneath the titration apparatus, ensuring that the pH meter is submerged in solution and that the mouth of the beaker is positioned in a way that will catch falling drops. Drop in a stir bar and turn on the plate so that the stir bar is spinning rather quickly.

B. Standardizing NaOH Once the apparatus has been fully prepped, you will titrate your KHP. Your first trial should be graphed with the AcidBaseTitration.cmbl file open. Once you have located and opened the correct file, press the green play button and then turn the bottom nozzle vertically, allowing drops of NaOH to flow. Allow the solution to titrate until well past its equivalence point; you can observe this on the screen of your instrument and within the beaker itself, as the solution will change colors. What would you expect to see at the equivalence point? When you have finished, press the stop button and turn the bottom nozzle horizontally. Save your trial by going to the File menu and clicking Save As. Make a new folder that is appropriately named for today’s experiments, as you will be saving all of today’s work in it. Once your graph is named and saved, open the Drop Counter-pH.cmbl file (refer to the introduction for its location). Repeat the experiment with this graphing method. In your notebook, record the approximate volume at which the solution changes color. Don’t stop collecting data until about 30 mL of NaOH have been added. Find the volume that corresponds with the equivalence point on the first graph. Find this equivalence volume on the second graph. What is the graph doing at this point? What are the moles of NaOH at the equivalence point of the reaction? Using this value and your estimated equivalence point volume, determine the concentration (in moles/L) of the NaOH solution.

C. Titrating Acetic Acid in Vinegar Each group will collect a sample of vinegar. You and your partner will titrate the acid in this vinegar with the NaOH you standardized. Measure a precise volume of vinegar into a beaker, add phenolphthalein, and begin collecting data. You may use either graphing method (pH or hydronium ion concentration) for these two trials. Make sure you save your graphs after each run, and name them appropriately. Find the equivalence point volume of NaOH, and use it to

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calculate the molarity of acetic acid in the vinegar solutions. Also, calculate the % acidity of your vinegar and compare it to the value given on the bottle. If you have LoggerPro on your personal laptop, you can simply insert your jump drive and save your graph to it (under the File menu similarly to most programs). If you do not have LoggerPro, you can click File → Export As → Text. You can then name your file and save it to your jump drive. This will save a text file of the data points you collected, and you will later have to copy and paste these points into Excel to recreate the graph you observed earlier. Outline of the Experiment

I. Standardize NaOH solution A. Titrate KHP using indicator; two trials, two different graphs B. Calculate molarity of NaOH solution to 4 sig. figs.

II. Determine acidity of vinegar solutions

A. Titrate vinegar samples two times B. Calculate molarity of acetic acid in vinegar C. Calculate % acidity of vinegar.

III. Compare values for different vinegars using class data

Laboratory notebook outline: Heading: Title, Date, Lab partners Prelab questions: Answer the questions in complete sentences. Show all calculations used to

answer these questions. Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to include

the specific glassware and measuring devices you will use and the amount of reagents. Data: Make a data table for your KHP titrations. You also will need data tables for your vinegar

titrations. Be sure that you always record the final and initial buret readings for your volume measurements.


clearly define the variables. All calculations should include proper units and final values circled. For this lab you will need to calculate the molarity of the NaOH, the molarity of acetic acid in vinegar, and the % acid in vinegar. Be sure to calculate the standard deviation of the class values if multiple trials were performed on a single sample. Include your values in a table of the class results for the vinegar titrations.

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Conclusions:

a. Which method of graphing do you prefer for finding the equivalence volume? Explain your choice.

b. How do the acidity values for vinegar vary within a given type of vinegar and between

different types of vinegars? Quantify you comparisons.

c. Why do labels use % acidity instead of molarity to report the concentration of acid in vinegar?

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Week 6: Neutralizing Power of Antacids Objectives: In this experiment you will study the neutralizing power of several commercial antacid tablets. Antacid tablets contain a material that will neutralize stomach acid (about 0.01 M HCl in normal stomachs, but higher after periods of stress and exciting weekends). Most brands use calcium carbonate as the active ingredient. The tablet could be directly titrated with 1.0 M HCl; unfortunately the end point would be very difficult to determine because of the slow dissolution of the tablet. A more efficient determination is to add an excess of HCl (more than enough to react completely with the CaCO3 and dissolve the tablet) and then titrate the leftover (unreacted) HCl with 1.0 M NaOH. This procedure is known as back-titration of the sample. The reactions are

CaCO3(s) + 2 HCl(aq) → CaCl2 (aq) + H2O(l) + CO2(g) (1) followed by (back titration with NaOH) HCl (aq) + NaOH (aq) → H2O(l) + NaCl(aq) (2) Prelab assignment: (Answer these questions in your notebook under a section titled Prelab Questions.)

1. a. For the first reaction between the calcium carbonate and the hydrochloric acid, which reactant will be the limiting reagent?

b. How do you know this? c. How could you test this experimentally?

2. Write the net ionic equations for the two reactions (1 & 2) given above.

Prepare for lab by writing up your procedure section and making up any data tables you will need. Leave room for making corrections or updates. In Class You will work in groups of two. Your group will be given a sample of approximately 1.0 M NaOH that has been standardized (make note of the concentration!) and approximately 1.0 M HCl. You must use the NaOH solution to standardize the HCl solution. For your procedure, think about what volume of HCl would be the best to use in the standardization titration. Discuss this with your lab partner. Use the Drop Counter and pH meter for your titrations in the same

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manner as last week. Before you begin titrating, there are several aspects about your equipment you should double-check: the drop-counter and pH sensor should be calibrated; a few drops of phenolphthalein should be in solution; the tip of the pH meter should be fully submerged; the stir bar should be agitating the solution. Make sure you press the data collection button before beginning your titration. If you have questions about your equipment, refer to last week’s procedure or ask your instructor. You can use the graphs you make to determine the solution’s equivalence volume, and further, the molarity of the HCl solution. Do your calculations in your lab notebook. Once your group has standardized the acid and base solutions, you will begin the reaction with the antacid tablet. Each group of students will study a different brand of antacid, and each student will analyze one antacid tablet. Begin by grinding a tablet into a powder with the mortar and pestle. Transfer as much of the powder as you can into a weigh boat, and measure its mass. In a 100 or 150 mL beaker, prepare a solution containing the ground-up tablet and 25 mL of HCl. What glassware is appropriate for this? Once the tablet has been dissolved, your solution may still look cloudy because of other components of the pill that do not dissolve in HCl. Titrate the remaining acid in each solution with your standardized NaOH using a phenolphthalein indicator. Make sure you press the data collection button before beginning your titration. In your notebook, record the approximate volume at which the solution’s color change takes place. Calculations (Be sure to show all of your work in your notebook!) You need to first determine the concentrations (molarity) of the NaOH and HCl solutions to 4 sig. figs. from your standardization data. Ultimately, you will need to find the grams of acid (HCl) neutralized per gram of antacid, and the grams of CaCO3 in each tablet. First, determine the moles of HCl that reacted with the antacid tablet. Remember: this is the moles of HCl that was used up in the first reaction, not the moles of HCl that remained at the end of the reaction! Once you have determined the moles of HCl that reacted with the antacid tablet, you can then calculate the grams of HCl reacted per gram of the tablet. This would represent the neutralizing power of each tablet. You will also use the moles of HCl that reacted with the antacid tablet to find the grams of CaCO3 in each tablet. You will need to take into consideration the stoichiometry of the balanced reaction shown in the introduction of this experiment. Record your average results and standard deviation for your group in your notebook for the grams of acid (HCl) neutralized per gram of tablet and the grams of CaCO3 in each tablet. You should also post these values on the class database. Compare the grams of CaCO3 to the value given on the product label and calculate the % error. As a class, you will discuss any differences between the various brands of antacids.

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Outline of the Experiment

I. Titrate HCl with NaOH and calculate molarity of HCl (to 4 sig. figs.) II. Determine neutralizing power of antacid

A. Mass antacid tablet powder, and record value in notebook B. Dissolve powder in an excess of standardized HCl C. Titrate excess HCl with the standardized NaOH D. Determine moles of HCl that reacted with the antacid E. Calculate the grams of HCl that reacted with each gram of tablet (neutralizing

power) F. Calculate grams of CaCO3 in each tablet and percent error based on label value

Laboratory notebook outline: Heading: Title, Date, Lab partners Prelab questions: Answer the questions in complete sentences. Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to include

the specific glassware and measuring devices you will use and the amount of reagents. Data: Make sure that you write down the concentrations of your reagents and the masses of

antacid powder. You will also need to record any important information from the package label.

Calculations and Results: Show all calculations. Be sure to give any formulas you used and

clearly define variables. All calculations should include proper units and your final values circled. Summarize the final results for your group with the average values and standard deviations for the grams of acid (HCl) neutralized per gram of antacid, and the grams of CaCO3 in each tablet. Compare your results to the values given on the package label and calculate % error. Also, make up a table of the class results for the various brands studied.

Conclusions:

1. How does the acid neutralizing power of the different antacids differ between different brands?

2. Explain the possible sources of these differences.

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Week 7: Prep for Leaf Lab / Journal Club Objective: Today, you will prepare several leaves for a future experiment concerning their decomposition. You will also take part in your first journal club, during which you will read published literature about the role of nitrogen as related to the decomposition of organic matter. Preparations for next week’s lab: Each student will need to obtain three airtight containers labeled A, B, and C. You will also need three 50-mL beakers and several leaves without stems. Transfer 25 ml of standardized NaOH into each beaker. For Containers A and B: record the mass of the empty containers in your notebook. Add four leaves each to Containers A and B, and record the mass of the containers and leaves in your notebook. Determine the mass of the leaves in each container. To Container A, use a disposable pipet to sprinkle 4 mL of deionized water on the leaves. To Container B, sprinkle 4 mL of 1% sodium nitrate on the leaves. Carefully place a 50-mL beaker containing the standardized NaOH in both containers A and B, making sure that there is no direct contact between the leaves and the NaOH solution. Transfer another 25 mL NaOH into the third beaker, and place it into Container C. This container will act as a control. Carefully seal the containers with their lids and label them with your name. Place them in a location designated by your instructor. Journal Club

Your instructor will give you more information on how to be well-prepared for Journal Club. Materials for this week and the pre-lab assignment will be posted on Moodle.

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Week 11: Decomposition of Tree Leaves5 Objectives: In this experiment you will use selective precipitation and titration to determine the amount of CO2 released per day from the decomposition of leaves. You will also study the effect of nitrate ions on this process. Over the past several decades, scientists have become concerned about the increasing amount of CO2 in our atmosphere. Carbon dioxide is a greenhouse gas that traps infrared radiation in the earth’s atmosphere leading to global warming. The increase in carbon dioxide in our atmosphere is primarily due to the burning of fossil fuels such as oil and coal. The process by which carbon moves through the atmosphere, biosphere, and geosphere is called the carbon cycle and is illustrated in the figure below6:

Figure 1. This carbon cycle diagram shows the storage and yearly changes of the carbon between the atmosphere, hydrosphere and geosphere in Gigatons - or billion tons - of Carbon (GtC).

5 Adapted from Wink, D. J.; Gislason, S. F.; Kuehn, J. E. Working with Chemistry; A Laboratory Inquiry Program; W. H. Freeman and Company: New York, 2000. 6 From http://earthobservatory.nasa.gov/Library/CarbonCycle/carbon_cycle4.html

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In this experiment, you will be investigating the role that plants play in the carbon cycle. Plants use the process of photosynthesis to convert carbon dioxide, water, and sunlight into glucose and oxygen gas. 6 CO2 + 6 H2O + hν (light energy) à C6H12O6 + 6 O2 (1) The glucose is converted to form other organic compounds that are used as building materials for the plant. When plants decompose, bacteria and fungi break down the leaves and release CO2 in the atmosphere. Scientists want to know the rate of this decomposition process so that they can better understand how increased amounts of CO2 in the atmosphere are impacting the carbon cycle. You will be studying the amount of CO2 released by a sample of leaves over the period of one week. To determine the amount of CO2 released by the plants, you will place the leaves in an airtight storage container that also contains 25.00 mL of NaOH that you standardized the previous week. The CO2 will react with NaOH as shown in the following equation: 2 NaOH(aq) + CO2(g) à Na2CO3(aq) + H2O(l) (2) After one week, your solution should be a mixture of the Na2CO3 and excess NaOH. As in the experiment last week, you will need to do a back titration with HCl to determine the amount of NaOH remaining in solution, and then calculate the amount of CO2 that reacted with the original NaOH solution. But in this experiment, there is an additional complication. The Na2CO3 that was formed in solution can also act as a base and would react with the HCl in the back titration reaction. You must first remove the Na2CO3 before performing the back titration. This can be done by selectively precipitating the CO3

2- ions while leaving the OH- ions in solution. This is not a trivial task since both carbonate ions and hydroxide ions tend to easily form precipitates. You will need to do some preliminary testing with a variety of cations to find a suitable cation that will form a precipitate with carbonate but not with hydroxide. Since you only have one chance to do your titration on your leaf sample, you will test out your protocol using a test solution containing a mixture of NaOH and Na2CO3. Once you are confident in your ability to accurately detect the amount of these species in solution, you can begin working on the leaf solutions. Nitrates are often used in fertilizers to increase plant growth. They also increase the growth of algae and bacteria which can disrupt the oxygen levels in aquatic ecosystems. To study the effect of nitrates on the rate of leaf decomposition, you also made up a leaf sample containing 4 mL of 1% nitrate, but otherwise identical to your other sample. The third sample contains only the sodium hydroxide solution in the airtight container and will be used as a control sample for comparison or point of reference.

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Prelab questions: (Answer the following in your notebook in a section labeled Prelab questions) 1. If there is any Na2CO3 remaining in the solution, it will neutralize some of the HCl used in the back titration. Write a balanced equation for the reaction that would occur between HCl and Na2CO3. Write both the molecular equation and the net ionic equation. 2. To determine which cation will precipitate carbonate ion but not hydroxide ion, you will be given 0.1 M solutions of Na2CO3, NaOH, AgNO3, KNO3, Sr(NO3)2, and Mg(NO3)2. Devise a series of reactions you and your partner can perform to do this determination. You will run these experiments in small test tubes. For each reaction you will do, write out the net ionic reaction that would occur if a precipitate were to form. 3. What effect do you think nitrate ion will have on the decomposition rate of the leaves? Defend your hypothesis in two or three sentences. 4. Begin writing out your procedure section and data tables in your lab notebook. Make a table in your data section to record the results of the reactions you described in Question 2. In class: Part I Begin by performing the test experiments you devised in pre-lab Question 2 with your partner. You only need to use 5-10 drops of each solution for each reactant. Record your results of these reactions in you laboratory notebook in the data section. All solutions containing Ag or Sr should be disposed of in a waste bottle in the hood. All other solutions can go down the sink. Part II.A Once you have found the cation you will use for your precipitation reaction, your instructor will give you an unknown test solution containing a mixture of 1.0 M solutions of NaOH and Na2CO3. Each group member will be given a different solution to analyze. Record the letter corresponding to your unknown solution in your notebook. Begin by accurately transferring a known volume of the solution to an Erlenmeyer flask and adding phenolphthalein indicator. The indicator should be pink since the solution is basic. Titrate the solution with standardized HCl until the solution just turns colorless and record the volume of HCl at the endpoint. Remember that in your actual sample you will not have the opportunity to do a rough titration, so be careful in your titration. Since the phenolphthalein color will fade on its own over time due to a reaction in O2, you should add an additional drop of indicator when you have finished titrating to confirm you have reached the equivalence point; if you have, the solution will remain colorless.

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Part II.B Transfer a second sample of the unknown solution into a clean flask but this time add an excess of the metal cation you earlier determined as suitable for the selective precipitation of carbonate. To determine how much would be an excess of the solution, assume the solution is completely 1.0 M Na2CO3 and then calculate what volume of the cation solution you would need to react with all of the carbonate ion. Record your observations in your notebook. After the precipitate has formed in the solution, titrate the sample with HCl using the phenolphthalein indicator as described earlier. Calculate the molarity of NaOH in your unknown mixture and the percentage by volume of NaOH in the mixture. Check your answer with your instructor. If you are not within 5% of the actual value, repeat the analysis with a new sample. Part III Once you have successfully characterized the unknown solution, you are ready to analyze your leaf samples. Using your results from the earlier trials, devise a procedure to analyze the amount of NaOH that reacted with CO2 in each of the three containers. Remember to run the analysis on the control sample (without leaves) in an identical manner as the other two. Finally you will need to calculate the mass of CO2 produced per day per gram of leaves in each of the two experimental samples. Remember that even without the decomposing leaves there is some CO2 in the container, but you need to determine the amount of CO2 that was produced due only to the leaf decomposition. Outline of Experiment I. Determine the cation that will selectively precipitate carbonate but not hydroxide ion. II. Determine the amount of NaOH in unknown solution containing NaOH and Na2CO3. a. Titrate sample with HCl. b. Precipitate the carbonate ion in a second sample and then titrate with HCl. c. Calculate the molarity and % by volume of NaOH in solution. d. Compare to actual value provided by your instructor. III. Determine Amount of CO2 given off by leaves a. Analyze sample with leaves, sample with leaves and nitrate, and control. b. Determine amount of CO2 in each sample.

c. Calculate the mass of CO2 produced per day per gram of leaves in each sample.

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Laboratory notebook outline: Heading: Title, Date, Lab partners Prelab questions: Answer the questions in complete sentences or chemical equations. Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to include the specific glassware and measuring devices you will use and the amount of reagents. Remember to include the procedure for preparing your samples from last week. Data: Make a data table for your observations in the precipitation study. You also will need

data tables for each of your titrations. Be sure that you always record the final and initial buret readings for your volume measurements. You should also include any observations of precipitation reaction that occur in your analysis of the unknown solution and the leaf samples.


clearly define variables. You should be sure to include your calculations for the molarity and % volume of NaOH and Na2CO3 in your unknown solution, the amount of CO2 in each of the three containers, and the mass of CO2 produced per day per gram of leaves in the sample containing leaves with water and the sample containing leaves with nitrate. These calculations may have several parts so be sure to show them all in your laboratory notebook. Circle and clearly label your results for each of the three sections outlined above. Also include a class data table which gives the amount of CO2 produced in leaf samples with and without added nitrate.

Conclusions:

1. Describe how your results compare numerically to those of your classmates. Explain any differences you observe.

2. What effect did the nitrate ion have on leaf decomposition? Is this what you would have

expected?

3. If leaves are approximately 44.5% carbon, how many days would it take for all of the carbon to be converted to CO2 using the class average rate calculated.

4. If you were to do an expanded study on this topic, give four other variables you could

study. How do you think these variables change the results of your experiment?

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Writing a Scientific Laboratory Report At the end of Module 2, you will turn in a typed laboratory report detailing your results from the leaf decomposition lab (Week 7). Your paper for this lab project is due at the beginning of your lab period the week of November 6. The format is as follows:

Title Sheet

This cover page should include a title, lab section, date, and names of the investigators involved.

Abstract

Give a concise summary of the project in one single-spaced paragraph (all other sections should be double-spaced). What were you trying to accomplish in this laboratory project? What was the result?

Introduction Give an overview of the background information necessary for the reader’s understanding of the significance of the experiment. This includes an introduction to any experimental techniques used, as well as a discussion of the relevance of this study. Describe the theory behind any method used in the experiment. In this case you will want to discuss titration and selective precipitation as well as why scientists would care about the amount of CO2 in the atmosphere and the effects of nitrate. In this section you must use outside sources and should cite any references used.

Experimental Procedure

Describe in detail the investigations you did with your lab partner(s). This should be double-spaced and in paragraph form. Give the procedure you used, but not the results at this time. Give all materials and reagents used. Be sure you include the procedure for setting up the leaf samples from the previous week. If you perform a reaction, give a balanced equation. An investigator should be able to duplicate your procedure from this description. This section should be a narrative of what you did in the lab. It should be written in the past tense and in passive voice.

Results and Observations This should give the results of your experiments and not be a discussion of why they occurred. You also need to explain the procedure you used to determine your final values from your raw data. In this case you need to explain how you determined the g of CO2 released per g of leaves per day for each sample beginning with the volume of HCl in your titration. For the investigations you did, you should detail your results and any observations or problems you encountered. You should include tables for all of the data collected.

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Discussion In this section you will discuss your results. Were your results as you anticipated? If not explain why. From your results, how did you determine the proper precipitating agent? You also need to compare your result to those of your classmates and explain any overall trends or differences you observe. Are there any experimental problems that give error in the experiment (human error is not an acceptable response here)? Be as specific as possible about any assumptions you have made in your analysis of results.

Conclusion How does all of the information presented above lead you to meeting the outcome desired for the lab project? Summarize the final outcomes you obtained. A well-written report should be at least 8-10 pages.

Notes:

• Students should review the definition of plagiarism in the BSC Honor Code. If you are uncertain, ask for help at the writing center or from your instructor. Ignorance is not an excuse. You may not look at lab reports of other students (former or present) in preparing your report. Your report will be submitted to Turnitin.com to check for similarities between papers.

• All tables included in your paper should be numbered (i.e. Table 1) and have a

meaningful title shown above the table. Graphs and figures should also be numbered and have a detailed caption below the figure. Equations or reactions should be indicated with a number in parenthesis on the right side. All tables, graphs, and figures should be referred to in the body of the paper and should not be broken by a page break. The reader should be able to independently read the table or graph and get all the information needed without having to read the laboratory report. Refer back to pages 30-31 for examples.

• References should be presented in American Chemical Society format. Refer to pages 31

and 32 for more information.

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CH 120 Laboratory Module 3 Calorimetry

Week 9: Introduction to Calorimetry Week 10: The Acidity of Vinegar Week 11: What Properties Make a Good Fuel? Week 12: Group Work on Poster Week 13: Poster Presentations Skills for this module: In this module you will perform a variety of measurements and draw conclusions based on the resulting data. In the process you will learn the following techniques: 1. Using a calorimeter to find the q and ∆H for an aqueous reaction. 2. Plotting the change in temperature over time to find extrapolated final temperature. 3. Using calorimetry and ∆H to find the concentration of a reactant. 4. Measuring the amount of heat used to raise the temperature of water in order to calculate the ∆H of a combustion reaction.

Outcomes: By the end of the module you should have: 1. Determined how the mass of reactant and mass of water affect ∆T and qrxn. 2. Determined the enthalpy change associated with two different dissolution reactions. 3. Determined the acidity of a variety of commercial vinegars using calorimetry. 4. Determined the ∆H of combustion for a variety of fuels. 5. Determined the chemical properties of compounds that would make the best fuels. Final Product: At the end of the module, your lab group for Week 10 will produce a poster presentation of your results from the fuel properties lab (Week 11). Your poster for this lab project is due on Moodle before lab on November 27, as you and your group will present your poster to your lab instructors that day in place of your regular lab period. You will sign up for a fifteen minute presentation timeslot prior to lab. Refer to page 81 for more information.

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Week 9: Introduction to Calorimetry7

Objective: In this experiment you will determine the enthalpy change associated with two different dissolution reactions. If we want to determine the enthalpy change of a chemical reaction we cannot measure it directly. Instead, we can use a technique called calorimetry to measure the change in temperature associated with the reaction. Although temperature change is related to the heat transfer, heat and temperature are not the same things. We have to consider other factors as well. In this experiment, you will investigate how temperature and heat are related and what other variables need to also be considered in finding the enthalpy change. In these experiments you will be using an insulated test tube called a calorimeter to minimize heat transfer outside of the vessel. In these experiments the calorimeter will contain water. If the reaction is endothermic, the water will provide heat for the reaction and the temperature will decrease. If the chemical reaction is an exothermic process, the water will absorb the heat that is released and the temperature will increase. You can assume for these experiments that the water has a density of 1.00 g/mL and a specific heat of 4.184 J/g°C. Remember: you are measuring the heat of the solution, but you will need to calculate the heat of the reaction. In class: Part I. How is the enthalpy change of a reaction related to temperature change? Section A: You will work in pairs for this experiment. If your lab session is using the LabQuest2, make sure your temperature probe is hooked into the “CH1” port prior to data collection. If you are using a laptop, be sure to hook the temperature probe into the “CH1” port on the LabQuest Mini, which in turn should be plugged into the USB port on your laptop. Regardless of which instrument you are using, check that that blank graph displayed is labeled correctly: temperature on the Y axis and time on the X axis. Begin your experiment by adding a measured volume of water into your calorimeter and placing the temperature probe inside. Make sure you record the volume of water you used in your notebook. Next, measure out a sample of CaCl2 and record its mass. Press the Collect Data button on your instrument, and add the CaCl2 to the calorimeter. Not sure how much solute to start with? Try about a gram. Is all of the solute immediately dissolving upon being added to the water? Would stirring the solution affect the temperature change of the solution? How? The change in temperature should be at least 3°C, and if it is not, adjust the mass of your next sample. Your lab group should do a total of three samples using different masses of CaCl2 using

7 Adapted from Teichert, M. A.; Stacy, A. M.; Rico, A. C.; Kegley, S. E.; Molinaro, M.; Walden, S. E. Computer Chip Thermochemistry; How Can We Create an Integrated Circuit from Sand? W. W. Norton & Company: New York 2003.

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the same volume of water and with each ΔT value being at least 3°C. Be sure to store each run as you complete it. Section B: Next, your group will do three trials in which the mass of CaCl2 is constant, but the mass of water in the calorimeter varies. Since you are assuming the density of water to be 1.00 g/mL, you can measure the volume of water instead of the mass for each trial. Once again, aim for a ΔT of at least 3°C. Be sure to record your constant mass of CaCl2 as well as your three different masses of water. You should also clearly take note of which runs correspond with the different masses of water and solute you’ve used for your trials in both Part A and B. Section C: For each graph you obtained, extrapolate the two sides of the curve to obtain the maximum temperature the solution reached after the addition of calcium chloride. (Your instructor will give you more information as to how this is done.) Use this maximum temperature to calculate the ΔT of the reaction. With this value, your group should be able to predict the composition of two solutions with different masses of calcium chloride and water that would give the same temperature change. You should record your prediction in your notebook and then perform the experiment using several trials to test your predictions. Calculate the q for each reaction. Remember that you are you are not measuring the q of the reaction directly, but the q of the aqueous solution. Each group will present their results to the class and the data between different groups would be compared. Using the group data, calculate an average ΔH and standard deviation for the dissolution of CaCl2 in water. Part II. How does the identity of the solute affect the enthalpy change? Once the class has calculated the ΔH for the dissolution of CaCl2, your group will perform a similar experiment to determine the ΔH for the dissolution of ammonium nitrate. Repeat the experiment with a several different volumes of water and masses of solute. Again, make sure the ΔT for each trial is at least 3°C, and record the masses of water and solute you used for each trial in your notebook. Calculate a standard deviation of your results and compare them to those collected by other groups. Outline of the Experiment I. How is ΔH for dissolution related to ΔT?

A. Determine the how the mass of CaCl2 affects the value for ΔT. B. Determine how the mass of water affects the value of ΔT. C. Determine the maximum temperature of the solution after the addition of CaCl2. D. Predict two solutions with different masses of water and CaCl2 that will give the same ΔT. Test your predictions experimentally and calculate the value of q for each trial.

E. Calculate ΔH for dissolutions of all trials from your group. Calculate an average ΔH and standard deviation for dissolution and put into class data base.

II. Experimentally determine ΔH for dissolution of NH4NO3 in water.

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Laboratory notebook outline: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to include

the specific glassware and measuring devices you will use and the amount of reagents. Data: Since most of your data will be collected by either the LabQuest2 or a laptop, you should

only record the mass of solute and volume of water for each trial you run. For example, you may want to make a table similar to the following:

Run # Mass H2O Mass Solute ΔT


clearly define variables. All calculations should include proper units. For this lab you need to calculate ΔH for the dissolution of CaCl2 and NH4NO3 with standard deviations. You will need to include your graphs for showing the how the mass of CaCl2 and water affect the value of ΔT. Describe how your actual results for Part I, Section C compare to your predictions. Include any class data values with standard deviations.

Conclusions:

1. Discuss how your results compare numerically to those of your classmates. Explain any differences you observe.

2. In Part I, Section C, you devised two trials that would give the same temperature change.

If ΔT were the same in these trials, is the amount of heat released the same? Explain why or why not?

3. How does the sign of ∆H for dissolution compare to the sign of ∆T? Explain your answer.

4. How do each of the following factors relate to each other (directly proportional, indirectly

proportional, no relation)? ∆T and the mass of the reactant ΔT and mass of water in calorimeter ∆H and the mass of the reactant

5. If you wanted to raise the temperature of 125 g of water from 25°C to 50°C, how many grams of CaCl2 would you need to add? Show your calculations.

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November 6: The Acidity of Vinegar Objective: In this experiment, you will determine the acidity of a variety of commercial vinegars using calorimetry. In the past, you have used titrations to determine the acidity of different vinegars. This week you will be using calorimetry instead of titration. You will also be responsible for designing the procedure for this experiment. You will be provided with a LabQuest2/LoggerPro, a temperature probe, a calorimeter, pipets, standardized solutions of approximately 1 M NaOH and 1 M CH3COOH, and a variety of vinegar solutions. As in the titration experiment, you will use of the acid/base reaction: CH3COOH(aq) + NaOH(aq) à NaCH3COO(aq) + H2O(l) (1) Prelab assignment: Design a procedure to determine the molarity of acetic acid and the % acidity of the vinegar solutions. Write this in your notebook including as many details as possible. Leave room in your lab notebook to make changes or additions to your procedure if needed. At the beginning of class you will discuss your procedure with your lab group and instructor. In class: In your groups, decide on a final procedure and update your notebooks. Discuss your protocol with your instructor or TA. Be sure to accurately record your experimental procedure in your lab notebook, along with all data you collect. Laboratory notebook outline: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to include

the specific glassware and measuring devices you will use and the amount of reagents. Data: Make a data tables for your calorimetry measurements. You will graph your data as

shown in the introduction to find ΔT for each trial. Graphs must include a meaningful title and the axes must be labeled with units.


clearly define variables. All calculations should include proper units. Your final calculations will include determining the molarity of your assigned vinegar solutions, and the % acidity of

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each. Calculate standard deviations whenever you perform multiple trials. Be sure all final results are circled and clearly labeled in your lab notebook. Compare your results to those given on the label of the vinegar. One copy of all graphs should be stapled to your lab notebook and another turned in with your carbon copies. Include a table of the class results for the different types of vinegars.

Conclusions:

1. How do the acidity values for vinegar vary within a given type of vinegar and between different types?

2. How did the results compare between using calorimetry and titrations?

Which technique do you believe is more accurate for this type of determination? What are some advantages and disadvantages of each technique (calorimetry and titration)?

3. If you were going to perform this experiment again, what modifications would you make

to the procedure that you had not originally considered when designing your protocol?

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Week 11: What Properties Make a Good Fuel? Objectives: In this experiment you will determine the ΔHcombustion for several different types of fuels. Then by comparing the chemical structure to the amount of heat released per gram of fuel you will determine what chemical properties are required to make a good fuel. With the ever increasing cost of petroleum products, scientists are actively pursuing possible alternative forms of fuel. These include oxygenated fuels such as ethanol from corn, or biomass derived from animal or vegetable waste. Some people have even converted their automobile to burn used cooking oil discarded from restaurants. Before designing an alternative fuel we need to first understand what chemical properties are needed to give the most amount of heat in the smallest possible mass. You will do this by measuring the heat released in the combustion reaction for a variety of fuels and compare these values to the number and types of bonds that make up the fuel. All of the fuels we will be studying are hydrocarbons that will produce water and CO2 upon combustion. Pre-lab assignment (answer in your notebook) 1. The fuels we will be using in this lab are listed below along with their skeletal structure for the carbon and oxygen atoms. Draw the Lewis structure for each compound using the concept of formal charge to give the best structure. You will need to draw in the missing hydrogen atoms. All of these compounds obey the octet rule. a. Hexane C6H14 C C C C C C b. Methanol CH4O C O c. Ethanol (also used in Sterno) C2H6O C C O

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d. Isopropanol C3H8O C C C O e. Butanol C4H10O C C C C O f. Cooking oil and margarine C18H30O2 O C C C C C C C C C C C C C C C C C C O g. Lamp oil C12H26 C C C C C C C C C C C C h. Paraffin or candle wax C40H82

C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C i. Wood - cellulose a polymer of glucose (shown below) C6H12O6

O

C O

C

O

C

O

CO

C

CO

(Note: Hydrogens are missing from structure) 2. For each of the fuels listed in Question 1 write a balanced combustion reaction on a separate

page in your lab notebook.

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In class:

In this experiment you use a series of fuels to heat a sample of water. By measuring the mass and the temperature change of the water, you can calculate the heat absorbed.

qwater = m × c ×ΔT for water c = 4.184 J/g °C

Since the water is absorbing heat, qwater should be a positive value. Theoretically the quantity of heat given off by the combustion of fuel is equal to the heat absorbed by the water, but in reality some of the heat will be lost to the surroundings. The heat of the combustion reaction, qcomb should be negative since this is an exothermic process. Before beginning the experiment you will need to record the mass of the burner you are using and the mass of water you will be heating. You should use approximately 100 grams of water in the metal can you are using for heating. Record the initial temperature of the water and then light your fuel burner. Monitor the temperature and let it rise by approximately 20°C. Adjust the flame to minimize the amount of soot formed during combustion. Record the highest temperature of the water and then extinguish the burner. Record any observations about the combustion in your lab notebook. Record the final mass of the burner to determine the amount of fuel used. For each fuel tested you should do three trials. For each fuel calculate qcomb, qcomb / g fuel used, and ΔHcomb. For some fuels you will be using an approximate molecular formula since the fuel may be a mixture of different compounds. As a class you will analyze the results of these reactions. How does the molecular structure relate to the amount of heat released by each fuel? Compare characteristics such as length of carbon chain, types of bonds, and number of oxygen atoms. Using your balanced equations from the pre-lab calculate the grams of CO2 released per kJ of energy released. Outline of Experiment I. Determine heat of combustion for fuels. A. Measure the ΔT for water heated and the mass of fuel consumed. B. Calculate qcomb C. Calculate qcomb/grams of fuel D. Cacluate ΔHcomb E. Calculate g CO2 released per kJ of energy released. II. Analyze data for trends A. Using class data rank fuels by the amount of heat released per gram B. Compare the heat released to the structure a. Compare oxygen containing versus non-oxygen containing fuels b. Compare longer carbon chains to shorter carbons chains

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Laboratory notebook outline: Heading: Title, Date, Lab partners Procedure: Write out a detailed stepwise procedure for your measurements. Be sure to include

the specific glassware and measuring devices you will use and the amount of reagents. Data: Make a data tables for each set of reactions your group performed. Also record any

observations you make for the combustion reactions. Be sure your values are recorded with the proper accuracy and units.


clearly define the variables. All calculations should include proper units. Average the results from your three trials for each fuel. For this lab you need to calculate qcomb, qcomb/ g fuel, ΔHcomb, and the grams of CO2 released per kJ of energy released. You need to include a final data table of the class results for the various fuels.

Conclusions:

1. Which fuel released the most heat per gram?

Which fuel released the least heat per gram? What structural characteristics were common to the fuels that gave off the most heat per gram.

2. Which fuel had the highest ΔHcomb?

Was the fuel the same as your answer for Conclusion a? Explain why or why not?

3. Which fuel gives off the least amount of CO2 per kJ of energy released?

Are fuels with lower amounts of CO2 released more or less efficient in terms qomb / mass of fuel?

4. Many states require cars to use gasoline containing oxygenated fuels.

What would be the advantages of using this type of fuel? How would it affect the miles per gallon?

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Week 12: Group Work on Poster At the end of module 3, your lab group for Week 11 will produce a poster presentation of your results from your fuel properties experiment. The poster is due on Moodle before lab on November 27. The poster will be created on a single PowerPoint slide using a template provided on Moodle. You can cut and paste text and figures on the template slide using the appropriate font sizes. Your group’s poster should contain the following sections:

Title Your poster should have meaningful title and include the full names of all students who are in your group.

Abstract

Give a concise summary of the project in one paragraph. What were you trying to accomplish in this laboratory project?

What was the result?

Introduction Give an overview of the background information necessary for the reader’s understanding of the significance of the experiment. In this case you will want to discuss titration and selective precipitation as well as why scientists would care about the amount of CO2 in the atmosphere and the effects of nitrate. In this section you must use outside sources and should cite any references used.

Experimental Procedure

Unlike a lab paper, you do not have to give every experimental detail in this section. You do want to give the reader a basic understanding of what you did. Give a balanced equation for all reactions you performed. You will want to give a general description of your experimental apparatus and may want to include a sketch or photo. This section should be written in the past tense and in passive voice (no personal pronouns).

Results and Observations This should give the results of your experiments and not be a discussion of why they occurred. You should include tables and/or graphs for all of your results that are numbered and have meaningful captions. Briefly (one or two sentences) highlight the most important results.

Discussion In this section you will discuss your results. Use bulleted sentences to draw the reader to the important points instead of paragraphs. How did your experimental

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values compare to the expected values? Can you explain any trends you observed in your results?

Conclusion

Give a brief paragraph summarizing your final conclusions. How does all of the information presented above lead you to meeting the outcome desired for the lab project. Summarize the final outcomes you obtained.

References List any references you used in introduction or discussion section using ACS format. You do need to have some references for your background information. These should be edited or peer reviewed sources (print or web) and not propaganda web sites such as you might find on a corporate or environmental web page.

Notes:

• Students should review the definition of plagiarism in the BSC Honor Code.

• Format your tables, graphs, and equations appropriately; see pages 30-31 for a review.

• All references should be presented in American Chemical Society format. You may use either endnotes or footnotes but indicate where the reference goes using a superscript in the text. Refer to pages 31-32 for a review.

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CH 120 Laboratory Kinetics

Week 14: Graphical Determination of the Rate Law Governing the Reaction of Sodium

Hypochlorite with Blue Food Colorant8 Objective: In this experiment, you will determine values for the reactant orders and the rate

constant of a reaction in order to determine its rate law. Chemical kinetics is the study of the rate at which chemical reactions take place. The rate of a particular chemical reaction may be dependent on such things as temperature, the type of solvent used, the presence of a catalyst, and the concentration of the reactants. One way chemists describe the kinetics of a particular reaction under certain conditions is by constructing a rate law. The rate law of the generic reaction A+ B + C → D + E is shown below.

Rate Law: Rate = k[A]x [B]y [C]z

A great deal of kinetic information is summed up in the rate law. The bracketed letters

represent the initial concentrations of the reactants. The exponents represent numbers that express the degree that the concentration of each reactant affects the overall rate. For example, if x = 1 then the reaction is said to be first order with respect to A. Doubling the concentration of A would increase the rate by a factor of 2. If y = 0, then the rate is independent of the concentration of B and is zeroth order with respect to B. If z = 2, the reaction is said to be second order with respect to C and doubling the concentration of C would increase the rate by a factor of 4. The overall reaction order is found by summing all of the exponents in the rate law. In this case, the overall order is 3. The k in the rate law is the rate coefficient. It accounts for all other factors that affect the rate including temperature.

Chemical reactions that involve the appearance or disappearance of color can be monitored with a spectrophotometer. The reaction of sodium hypochlorite (NaOCl), the active ingredient in bleach, with the food colorant FD&C Blue #1 is one such reaction. Using a spectrophotometer and graphical analysis software, you will devise a procedure that will determine the entire rate law for this reaction.

In these reactions the NaOCl will be in a large excess over the blue food coloring and its concentration will not change significantly during the course of the reaction. Therefore in the rate expression Rate = k[NaOCl]x[Blue]y both k and [NaOCl]x will be constant. We can rewrite the rate expression as Rate = kobs[Blue]y where kobs is the observed rate constant and kobs = k[NaOCl]x. In the first experiment you will be determining the reaction order for the blue food coloring, y, by monitoring the change in concentration of the blue food coloring over time at its maximum absorbance of 630 nm. In the second experiment, you will halve the concentration of [NaOCl] and determine its reaction order, x, from the change in kobs.

8 This laboratory was adapted from Arce, J.; Bentacourt, R.; Rivera, Y.; Pijem, J. J. Chem. Ed. 1998, 75, 9, 1142 by John Owen.

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Pre-Lab (do you work on this page instead of your lab notebook) Name____________________________ Lab Section________________ Graphical Determination of the Rate Law Governing the Reaction of Sodium Hypochlorite

with Blue Food Colorant

a. The bleach solution you will be using is 3.00% by mass NaOCl. Assuming the density of the solution is 1.00 g/mL, what is the molarity of NaOCl in bleach. Show work.

b. You will run the first trial at a ratio of 25:1 Blue #1 stock to bleach by volume. What will be the molarity of NaOCl in this final solution?

Below is some sample data for the experiment. The absorbance at 630 nm is proportional to the concentration of Blue #1. Construct three graphs that will help you determine if the reaction order is best described as zero, first, or second order with respect to Blue #1. Determine the slope of the linear graph. Determine the value for k with proper units and record it on the graph. Attach these graphs to this page to be turned in.

Time(min.) Absorbance

1 1.65

2 1.24

3 0.930

4 0.710

5 0.530

6 0.390

7 0.290

8 0.220

9 0.165

10 0.123

11 0.092

12 0.069

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Procedure A. Observe Fill a cuvette about 3/4 of the way with DI water, and remove any fingerprints from the smooth surface with a KimWipe. This is called a “blank.” ** When placing a cuvette into the spectrometer, make sure that the sides of the cuvette with ridges are facing left and right, ensuring that the beam of light will shoot through the smooth sides.

LabQuest2: Laptop: 1. Tap the red box on the Meter screen, and select “Calibrate.” Follow the instructions, then press OK. At the top of the first screen, select “Sensors” and “Data Collection.” Change the Mode to “Full Spectrum.” Do not change any other settings. Tap OK. 2. Fill a cuvette with Blue #1, wipe it, place it into the spectrometer, and press play (collect data). Wait a few seconds, then press the stop button. Remove the cuvette.

1. Plug the spectrophotometer into the laptop, and open LoggerPro. You should see a rainbow gradient on the screen; if not, open the Experiment drop-down menu and click Data Collection. Change the Mode to “Full Spectrum.” 2. Place the blank into the spectrometer, click Experiment, click Data collection, hover over “Calibrate,” and select Spectrometer 1. Allow the spectrometer to warm up, and then click “Finish Calibration.” When the numbers stop changing, press OK. Remove the cuvette from the machine. 3. Fill a second cuvette with Blue #1, wipe it, place it into the spectrometer, and press the Collect Data button (green play button) in the top right area of the screen. Wait about five seconds, then click the stop button. Remove the cuvette. A graph and a list of coordinates should be visible on the screen.

Spectrometers measure the amount of light absorbed by colored solutions. At what wavelength does the blue dye’s maximum absorbance occur? Record this wavelength. At that point, what color light is being transmitted? Absorbed? 3. On the Meter screen, select “File,” then “New.” The data you just collected may be discarded.

4. Select “File,” then “New.” The data you just collected may be discarded.

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B. First Run

LabQuest2: Laptop: 1. Select “Sensors” at the top of the Meter

screen followed by “Data Collection.” Change the Mode to “Time Based.” The Rate should be set to 0.06667 samples/s and the Interval should be 15 s/sample. The Duration of the run should be 900 s (15 minutes).

2. Return to the Meter screen and tap the red box. Select “Change Wavelength” and enter the wavelength at which the blue dye’s maximum absorbance should occur.

3. Repeat the calibration process from Part A at this new wavelength (using water). Skip the lamp warm-up. When you have finished calibrating the machine, the Meter screen should read 0.000.

1. Select “Experiment” at the top of the screen, and then “Data Collection.” Change the Mode to “Time Based.” Change the Length to 900 seconds and the Sampling Rate to 15 seconds/sample. If this has been done correctly, the first box (samples/second) will read 0.06667.

2. Find the button that looks like a graph with a rainbow underneath. Click it, then select “Configure Spectrometer 1: Data Collection.” Under “Select Wavelength,” check ONLY the box next to the wavelength that the maximum absorbance of Blue #1 occurs at. Then, under “Set Collection Mode,” select Abs. vs. Time. Click OK.

A 25:1 ratio of Blue #1 stock solution to bleach by volume should ensure a complete reaction within 15 minutes. To assure rapid mixing, first add 1 mL of bleach into a small beaker. Measure out 25 mL of Blue solution in a graduated cylinder and add it to the beaker. Quickly and carefully transfer a portion of the bleach and dye mixture into a cuvette, filling it about 3/4 of the way. Wipe the cuvette, place it into the spectrometer, and begin collecting data. Since the run is time based, data collection will stop on its own. You may move on to Part C, but keep an eye on your device while the reaction is occurring. Once Run 1 has completed: 4. Tap the file cabinet on the upper right-hand

corner of the Graph screen to store the run. 3. At the top of the screen, click “Experiment” and then “Store Latest Run.”

Construct three graphs that will help you determine if the reaction order is best described as zero, first, or second order with respect to Blue #1. Determine the slope of the linear graph. What does this slope tell you?

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C. Second Run Keep the Blue #1 concentration the same and reduce the sodium hypochlorite concentration by one half. Think about how you will make up this diluted solution, and be sure to have your calculations approved by your instructor before proceeding. Run the experiment again using the lower bleach concentration. Do not mix your dye and bleach until Run 1 has been completed and its data stored. Be sure to store Run 2 upon completion. Graphically analyze the results. Compare these graphs with the last graphs you constructed. How can these changes indicate the order with respect to sodium hypochlorite? The pseudo rate coefficient (kobs) is related to the real rate coefficient by kobs = k[NaOCl]y. Note the NaOCl concentration can be calculated considering the bleach is 3.0% NaOCl and is diluted by the Blue #1 stock. D. Exporting Your Data 1. Unplug the spectrometer from the USB port and insert your flash drive. 2. After storing Run 2, navigate to the Table screen. Tap “File,” then “Save” and name your data. 3. Tap the USB icon on the top left of the screen. The screen that appears should list any other

files and folders your USB drive currently contains. Tap “Save” at the bottom of this screen to save your data to your flash drive.

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CH 120 Laboratory: Kinetics Graphical Determination of the Rate Law

Name: _______________________________ Lab Section: _________ Partner’s Name: __________________________

Data Sheet

1st Run:

Concentration of NaOCl in reaction solution = ___________ M

kobs 1 = ________________________ (give proper units)

2nd Run:

Concentration of NaOCl in reaction solution: ____________M

k obs 2 = _____________ (with proper units)

Order with respect to Blue #1:____________

Order with respect to NaOCl: ____________

k = ______________ (with proper units)

Rate law:______________________________

Be sure to turn in all of your graphs with this data sheet.

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