4. activity: data collection in your science classroom...

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4. Activity: Data Collection in your Science Classroom: Using Logger Pro Getting to Know Hands-on Experiments

All experiments use: Logger Pro software, Laptop

A. Evaporation and Intermolecular Attractions

In this experiment, temperature probes are placed in two liquids. Evaporation occurs when the probes are removed from the liquid’s container. "This evaporation is an EXOTHERMIC process (for the system) that results in a temperature drop (negative enthalpy ) for the SYSTEM. When the temperature drops for the system/solution, the system is releasing heat into the SURROUNDINGS, so the reaction is EXOTHERMIC for the SYSTEM (i.e., measured temperature drop on the system), and also therefore ENDOTHERMIC for the SURROUNDINGS (the surroundings are absorbing this heat, thus the enthalpy of the reaction for the surroundings is POSITIVE). The magnitude of a temperature decrease is, like viscosity and boiling temperature, related to the strength of intermolecular forces of attraction. In this experiment, you will study temperature changes caused by the evaporation of two alcohols and relate the temperature changes to the strength of intermolecular forces of attraction. You will use the results to predict, and then measure, the temperature change of a third alcohol liquid.

B. pH of Household Substances

In this experiment, litmus paper and a computer-interfaced pH sensor are used to determine the pH values of household substances.

Universal indicator will be added to calibrate the colors of the universal indicator over the entire pH range.

C. Beer's Law Determining the Concentration of a Solution

The primary objective of this experiment is to determine the concentration of an unknown cobalt(II) chloride solution. You will be using

a SpectroVis Plus. In this device, light from the LED and tungsten bulb light source will pass through the solution and strike a photocell.

The CoCl2 solution used in this experiment has a deep blue color. A higher concentration of the colored solution absorbs more light (and

transmits less) than a solution of lower concentration.

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4a. Activity: Evaporation and Intermolecular Attractions http://www.vernier.com/experiments/cwv/9/evaporation_and_intermolecular_attractions/

In this experiment, temperature probes are placed in two liquids. Evaporation occurs when the probe is removed from the liquid’s container. This evaporation is an endothermic process that results in a temperature decrease. The magnitude of a temperature decrease is, like viscosity and boiling temperature, related to the strength of intermolecular forces of attraction. In this experiment, you will study temperature changes caused by the evaporation of several liquids and relate the temperature changes to the strength of intermolecular forces of attraction. You will use the results to predict, and then measure, the temperature change for several other liquids.

You will encounter two organic alcohols compounds in this experiment. Methanol contains carbon and hydrogen atoms, in addition to the -OH functional group. Methanol, CH3OH, and ethanol, C2H5OH, are two of the alcohols that we will use in this experiment. You will examine the molecular structure of the alcohols for the presence and relative strength of the intermolecular forces—hydrogen bonding, dipole-dipole and dispersion forces.

MATERIALS Figure 1 Figure 2

Power Macintosh or Windows PC Vernier with Logger Pro Two temperature probes

methanol (methyl alcohol) ethanol (ethyl alcohol) 2 pieces of filter paper (2.5 cm X 2.5 cm) small rubber bands

Pre-Lab Exercise Prior to doing the experiment, complete the Pre-lab table. The name and formula are given for each compound. Draw a structural formula for a molecule of each compound. Then determine the molecular weight of each of the molecules. Dispersion forces exist between any two molecules and generally increase as the molecular weight of the molecule increases. Next, examine each molecule for the presence of hydrogen bonding. Before hydrogen bonding can occur, a hydrogen atom must be bonded directly to an N, O, or F atom within the molecule. Tell whether or not each molecule has hydrogen-bonding capability.

Procedure. Go to the following link for more information: http://www.vernier.com/experiments/cwv/9/evaporation_and_intermolecular_attractions/ 1. Obtain and wear goggles! CAUTION: The compounds used in this experiment are flammable and poisonous. Avoid inhaling their

vapors. Avoid contacting them with your skin or clothing. Be sure there are no open flames in the lab during this experiment. Notify your instructor immediately if an accident occurs.

2. Prepare the computer for data collection. Prepare the computer for data collection by opening the Experiment-9 folder from Chemistry with Vernier. Then open the experiment file that matches the probes you are using (09 Evaporation.cmbl).

On the Graph window, the vertical axis has temperature scaled in °C. The horizontal axis has time scaled in seconds. Click on the axis of the graph to change the range (max temperature and max time) if your instructor asks you to change these values.

3. Roll the tips of Probe 1 and Probe 2 with square pieces of filter paper secured by small rubber bands as shown in Figure 1. Roll the filter paper around the probe tip in the shape of a cylinder. Hint: First slip the rubber band up on the probe, wrap the paper around the probe, and then finally slip the rubber band over the wrapped paper. The paper should be even with the probe end.

4. Stand Probe 1 in the methanol container and Probe 2 in the ethanol container. Make sure the containers do not tip over. 5. Prepare 2 pieces of masking tape, (10-cm long), to be used to tape the probes in position during Step 6. 6. After the probes have been in the liquids for at least 45 seconds, begin data collection by clicking Collect . Monitor the

temperature for 15 seconds to establish the initial temperature of each liquid. Then simultaneously remove the probes from the liquids and tape them so the probe tips extend 5 cm over the edge of the table top as shown in Figure 1. Use the command Apple-T to extend the time collection if the experiment is to end before the temperature reaches a minimum.

7. When both temperatures have reached minimums and have begun to increase. Click Stop to end data collection after the temperature has begun to rise for at least 20 seconds. Click the Statistics button, , then click OK to display a box for both probes. Record the maximum (T1) and minimum (T2) values for Temperature 1 (methanol) and Temperature 2 (ethanol).

8. For each liquid, subtract the minimum temperature from the maximum temperature to determine DT. This is the temperature change during evaporation.

9. Roll the rubber band up the probe shaft and dispose of the filter paper as directed by your instructor. 10. Based on the DT values you obtained for these two substances, the information of n-propanol in the table below, plus information in

the pre-lab exercise, estimate a DT-value for n-butanol. Use your knowledge of intermolecular forces that you learned in Chem-200 to compare the strength of IMF for methanol, ethanol and propanol to help your estimation of DT. Record your predicted DT, then explain how you arrived at this answer in the space provided.

Processing the Data 1. Which of the alcohols studied has the strongest intermolecular forces of attraction? Which of the alcohols has the weakest intermolecular forces? Explain your answer using the results from this experiment. 2. Plot a graph of DT values versus molar mass, based on the table you completed. Use the template provided on the data sheet.

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Activity 4a Evaporation And Intermolecular Attraction ____ / __ Score Name (last)____________________(first)____________________

Lab Section: Day _________ Time _______

Substance name

Chemical Formula

Structural Formulas http://www.chemspider.com/

Molecular Weight Polarity & IMF Check (✓) all that applies

Methanol CH3OH

Polar ______ nonpolar ______

London Dispersion ______

Dipole-Dipole ______

H-Bonding ______ Ethanol C2H5OH




H-Bonding ______

n-Propanol C3H7OH

60.1 g/mol




H-Bonding ______

n-Butanol C4H9OH




H-Bonding ______

Experimental Observations and Notes

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Data table: Substance Tinitial (°C) Tfinal (°C) DT (T1–T2) (°C)

Ti1 Ti2 Ti3 Ti1 Tf2 Tf3 DT1 DT2 DT3

methanol

Ethanol

n-Propanol

6.1 ° C

n-Butanol

Your

Prediction _____°C

If n-butanol was used in this experiment, predict a value for DT and write it in the table above.

Use the graph at right to assist you in your prediction.

Complete the graph below based on the table above (Attached Excel graph) if you completed the graph using Excel..

Molar Mass

Justify your estimation for DT for n-butanol Explain the trend that is observed from the graph above. What can you conclude about IMF and its influence on DHevaporation of a compound?

Note: If you rip this page from the lab manual, be sure to trim the edge. (Reminder from your lab instructor.)

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4b. Activity: pH of Household substances http://www.vernier.com/experiments/cwv/21/household_acids_and_bases/

Many common household solutions contain acids and bases. Acid-base indicators, such as litmus and red cabbage juice, turn different colors in acidic and basic solutions. They can, therefore, be used to show if a solution is acidic or basic. An acid turns blue litmus paper red, and a base turns red litmus paper blue. The acidity of a solution can be expressed using the pH scale. Acidic solutions have pH values less than 7, basic solutions have pH values greater than 7, and neutral solutions have a pH value equal to 7

MATERIALS: household solutions ring stand wash bottle Power Macintosh or Windows PC 7 small test tubes utility clamp deionized water Vernier computer interface test-tube rack sensor soaking solution 250-mL beaker Logger Pro red and blue litmus paper stirring rod paper towel Vernier pH Sensor red cabbage juice

Procedure

1. Obtain and wear goggles. CAUTION: Do not eat or drink in the laboratory.

Part I. Litmus and Hydro-ion paper Tests

2. Label 7 test tubes with the numbers 1-7 and place them in a test-tube rack.

3. Measure 3 mL of vinegar into test tube 1. Refer to the data table and fill each of the test tubes 2-7 to about the same level with its respective solution. CAUTION: Ammonia solution is toxic. Its liquid and vapor are extremely irritating, especially to eyes. Drain cleaner solution is corrosive. Handle these solutions with care. Do not allow the solutions to contact your skin or clothing. Wear goggles at all times. Notify your instructor immediately in the event of an accident.

4. Use a stirring rod to transfer one drop of vinegar to a small piece of blue litmus paper on a paper towel. Transfer one drop to a piece of red litmus paper on a paper towel. Record the results. Clean and dry the stirring rod each time.

5. Use a stirring rod to transfer one drop of vinegar to a small piece of Hydro-ion paper on a paper towel. Note the color and compare the color to the color spectrum on the Hydro-ion paper chart. Record the results. Clean and dry the stirring rod each time.

6. Test solutions 2-7 using the same procedure as 4 and 5 above. Be sure to clean and dry the stirring rod each time.

Part II pH Vernier Probe Test http://www.vernier.com/experiments/cwv/21/household_acids_and_bases/

7. Prepare the computer to monitor pH by going to the folder Chemistry with Vernier and then opening the file “21 Household Acids.cmbl”. The computer will display a live pH reading.

8. Raise the pH Sensor from the sensor storage solution and set the solution aside. Use a wash bottle filled with deionized water to thoroughly rinse the tip of the sensor as demonstrated by your instructor. Catch the rinse water in a 250-mL beaker.

9. Before measuring the pH of the test solutions calibrate the pH probes with pH 4 and pH 10 buffered solutions if instructed by your professor. Use your largest test tube (one that can accommodate the pH probe) and fill to about a third. Go to the calibration menu in Logger Pro for the calibration procedure. After calibration, test your calibration with the pH 7 buffered solution

10. Obtain one of the 7 solutions in the small container supplied by your sensor. Raise the solution to the pH sensor and swirl the solution about the sensor. When the pH reading stabilizes, record the pH value.

11. Prepare the pH sensor for reuse by rinsing the pH probe with deionized water from a wash bottle. Place the sensor into the sensor soaking solution and swirl the solution about the sensor briefly. Rinse the probe again with deionized water.

12. Determine the pH of the other solutions using the Step 10 procedure. You must clean the sensor, using the Step 11 procedure, between tests. When you are done, rinse the tip of the sensor with deionized water and return it to the sensor soaking solution.

Part III Universal Indicator

13. After you have finished Part II, add 3 drops of universal indicator to each of the 7 test tubes. Record your observations. Dispose of the test tube contents as directed by your instructor.

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Acid-Base Indicator

http://chemistry.about.com/library/weekly/aa112201a.htm

pH Hydro-ion paper indicator

Cabbage Indicator

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Activity 4b: pH of Household substances ____ / __ Score Name (last)____________________(first)____________________


Data Table

Test Tube

Solution Blue Litmus Red Litmus Hydro-Ion Paper

Universal Indicator (Color)

pH Vernier Trial1 Trial2 Trial3 Average

1 vinegar

2 ammonia

3 lemon juice

4 soft drink

5 cabbage

6 detergent

7 baking soda

Processing the Data 1. Which of the household solutions tested are acids? How can you tell? 2. Which of the solutions are bases? How can you tell? 3. What color(s) is universal indicator in acids? What is it in bases? 4. Can universal indicator be used to determine the strength of acids and bases? Explain. 5. List advantages and disadvantages of litmus and universal indicators.

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6. Using the pH scale shown, list each test solution in its appropriate place on the pH scale.

For each test solution that you tested in this experiment, use the pH to calculate the hydronium ion [H3O+] concentration and

write this in the appropriate column below. Drano, blood, and battery acid are shown as examples.

Substance:

pH

[H3O+] M

Drano (Lye) 14.0 1.0e-14 M g Blood 7.40 3.981e-8 g

Battery Acid 0.00 1.0 M g

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4c. Activity: Determining the Concentration of a Solution: Beer’s Law The primary objective of this experiment is to determine the concentration of an unknown cobalt(II) chloride solution. You will be using a SpectroVis Plus shown in Figure 3. In the SpectroVis Plus, a range of light from 380 – 950 nm will pass through the solution. The CoCl2 solution used in this experiment has a blue color. A higher concentration of the colored solution absorbs more light (and transmits less) than a solution of lower concentration.

Figure3

Figure 4

Each standard solution is transferred to a small, rectangular cuvette that is placed into the SpectroVis Plus. The amount of light that penetrates the solution and strikes the photocell is used to compute the absorbance of each solution. When a graph of absorbance vs. concentration is plotted for the standard solutions, a direct relationship should result, as shown in Figure 4. The direct relationship between absorbance and concentration for a solution is known as Beer’s law. The concentration of an unknown CoCl2 solution is then determined by measuring its absorbance with the SpectroVis Plus . By locating the absorbance of the unknown on the vertical axis of the graph, the corresponding concentration can be found on the horizontal axis (follow the arrows in Figure 4). The concentration of the unknown can also be found using the slope of the Beer’s law curve. MATERIALS

Excel program CoCl2 solution of 0.010 M, 0.020 M, 0.050 M and 0.10M Vernier computer interface Stirring rod Logger Pro pipet pump or pipet bulb Vernier SpectroVis Plus Vernier cuvette tissues (preferably lint-free)

two small beakers test tube rack deionized water

Procedure for SpectroVis Plus 1. Plug the SpectroVis Plus into the computer via the USB cable.

2. Open Logger Pro. A blank plot displaying Absorbance vs. Wavelength (nm) should be displayed. If the x-axis reads Time or Concentration instead, clink on the “Configure Spectrometer” icon at the top (the one with a rainbow-filled area under a curve) and change the Collection Mode to Absorbance vs. Wavelength.

3. Fill cuvette 2/3 full with deionized water. In Logger Pro, calibrate the spectrometer by selecting “Calibrate” under the “Experiment” drop-down menu. When prompted for a blank cuvette, wipe down the cuvette with a Kim wipe and place it in the chamber with the clear sides facing the triangle and the white light icon. Remember the orientation, as you will need to put the cuvette into the chamber the same way each time.

4. Click on “Finish Calibration.” When calibration is complete, empty the cuvette then rinse it with small portions of your sample three times then fill it about 2/3 full. Wipe the cuvette and place it in the chamber with the same orientation as before.

5. Click on “Start Collection,” wait about 5 seconds, then click on “Stop Collection.”

6. Collect the spectra for the remaining samples using the same steps. Note that you do not need to re-calibrate the spectrometer.

7. Click on “Examine” to determine to the lmax’s and the absorption values. They should all have the same or very close lmax’s . Record the absorption values and the wavelength associated.

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Processing the Data 1. In Excel, plot absorbance versus concentration and apply a "Trendline" for a linear regression analysis. Do not include the

absorbance data of your unknown in the graph. Show the equation of the line and the correlation (R2) on the graph. Analyze the data to see if there is a correlation between concentration and absorbance. In fact, the linear regression should show a line that passes near or through the data points and the origin of the graph. Apply LINEST to the data and turn in the table and graph with your activity.

2. Obtain a printout or digital copy (as directed by your instructor) of absorbance vs. concentration with regression line displayed.

3. In addition get the Beer's Law equation, A = ebc.

a) If b is 1.0 cm, what is the value of e?

b) What is the correlation factor, "R2 " for your data set? What does this tell you?

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Activity 4c: Determining the Concentration of a Solution; Beer’s Law ____ / __ Score Name (last)____________________(first)____________________


Experimental Observations and Notes

DATA and calculations Standard solution

CoCl2 (aq)

Unknown No. __________

Trial Concentration (mol/L) Absorbance

1 0.010

2 0.020

3 0.050

4 0.100

5 Unknown solution:

Concentration of unknown mol/L

Note: If you rip this page from the lab manual, be sure to trim the edge. (Reminder from your lab instructor)

4. activity: data collection in your science classroom...

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