skill check initiating and planning exploring conversions between mass and...

Inquiry I N V E S T I G AT I O N 5-A

Exploring Conversions between Mass and ParticlesIn this investigation, you will work with two units of quantity: the dozen and the mole. You will practise converting a dozen into individual items, and vice versa. You might ask, “How is working with a dozen useful in chemistry?” In the second part of this investigation, you will apply the skills you learned while working with a dozen to determine quantities of diff erent sample substances.

Pre-Lab Questions

1. How would you convert 10 dozen into a number of items? Describe the steps you would follow, and perform the calculation.

2. How would you convert 10 moles into a number of particles? Describe the steps you would follow, and perform the calculation.

3. Read the Procedure and then explain why it is important that you use the same 50 mL beaker in Part 1 and Part 2 of the investigation?

4. How would you determine the amount in moles of a sample, if you are given only its mass?

Questions

How can you use units of quantity, such as a dozen and a mole, to count small objects and particles and to determine mass? How can you use mass to determine quantities of a substance and number of particles?

Procedure

Part 1: Counting and Measuring the Mass of Beans

1. Read steps 2 to 5 in this Procedure, and create a table to record your results. 2. Count out one dozen of one type of bean. 3. Measure the mass of the 50 mL beaker. Record your result. 4. Fill the beaker with the dozen beans. Measure the mass of the beans and

beaker. Record your result. 5. Repeat steps 2 to 5 for each type of bean you have been given.

Part 2: Measuring the Mass of Chemicals

6. Read steps 7 to 11, and create a table to record your results. 7. Measure the mass of the sample of copper given to you by your teacher.

Record your result. 8. Determine the molar mass of copper from the periodic table. Record this

value in your table. 9. You have already measured the mass of the 50 mL beaker in Part 1. Add

10 mL of sodium chloride to the beaker. Measure the mass of the sodium chloride and the beaker. Record your result.

10. Determine the molar mass of sodium chloride from the periodic table. Record this value in your table.

11. Repeat steps 9 and 10 using distilled water instead of sodium chloride.

S k i l l C h e c k

Initiating and Planning

Performing and Recording

Analyzing and Interpreting

Communicating

Materials

• 1 dozen dried kidney beans (or another type of large bean)

• 1 dozen dried chick peas (or another type of bean of similar size)

• 1 dozen dried lentils (or another type of bean of similar size)

• small piece of copper wire, Cu(s)• 10 mL of sodium chloride (table

salt), NaCl(s) • 10 mL distilled water, H2O(�)• 50 mL beaker• balance• graduated cylinder

✓

✓

✓

244 MHR • Unit 3 Quantities in Chemical Reactions

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Analyze and Interpret

Part 1

1. For each type of bean, calculate the mass of the dozen beans in the beaker.

2. From the net mass found in step 1, calculate the average mass of a single bean for each type of bean.

3. For each type of bean, calculate the number of beans in 3.5 dozen. Th en calculate the mass of 3.5 dozen beans.

4. For each type of bean, calculate how many dozen beans you would have if you had 25.0 g of beans. How many individual beans would you have?

Part 2

5. Use the mass and the molar mass of each substance you measured to calculate the amount in moles of each sample. Remember to calculate the net mass for the sodium chloride and water samples.

6. Determine the number of atoms of copper, molecules of water, and formula units of sodium chloride in the samples you were given.

7. Calculate the mass of 1 mol of each substance. 8. Calculate the mass of one particle (atom of copper,

molecule of water, and formula unit of sodium chloride) of each substance.

9. Calculate the number of particles in 3.0 mol of each substance.

10. Calculate the mass of 5.0 mol of each substance. 11. Calculate the amount in moles of each substance

in 100 g of the substance.

Conclude and Communicate

12. What general strategy or formula could you use to convert a dozen items to individual items, and vice versa?

13. What general strategy or formula could you use to convert a number of dozen items to the mass of the items, and vice versa?

14. What general strategy or formula could you use to convert the mass of a substance to the mass of one particle of the substance?

15. What general strategy or formula could you use to convert the mass of a substance to the amount in moles of the substance?

16. What general strategy or formula could you use to convert the amount of a substance to the number of particles of the substance?

17. Compare the strategies or formulas you used in Part 1 with the strategies or formulas you used in Part 2. How are they similar?

Extend Further

18. INQUIRY Design an investigation that will enable you to answer the following question: What amount in moles of calcium carbonate, CaCO3(s), is in one tablet of a given calcium supplement? Assume that the supplement contains only calcium carbonate.

19. RESEARCH Research how knowledge of chemical quantities is important in the education, training, and work of environmental chemists.

Chapter 5 The Mole: A Chemist’s Counter • MHR 245


Inquiry I N V E S T I G AT I O N

S k i l l C h e c k

Initiating and Planning

Performing and Recording

Analyzing and Interpreting

Communicating

Safety Precautions

• Tie back loose hair and clothing. • Do not touch the lit candle.• Be careful not to spill any molten

wax on your hands.

Materials

• paraffi n wax candle (tea light)• wooden splints• water• sodium chloride (table salt),

NaCl(s)• sucrose (table sugar), C12H22O11(s)• weighing paper• paper• wax crayon• balance• clock or timer• small paper clip• beaker• 10 mL graduated cylinder • medicine dropper• 50 mL graduated cylinder• ruler

✓

✓

✓

Using the Mole for Measuring and Counting ParticlesTh e mole is used to group large numbers of particles (atoms, molecules, ions, and formula units) of a substance. Chemists can use the mole to determine how many particles of a substance they are working with. In this investigation, you will use the mole concept to practise measuring and counting atoms, molecules, and other particles of diff erent substances.

Pre-Lab Questions

1. List safety precautions you should take when working with a candle in a laboratory.

2. Write a plan to fi gure out the amount of candle wax that burns over a period of time and the rate at which it burns.

3. Describe the correct method for measuring a crystalline solid, such as table salt or table sugar, on a balance.

Question

What are some methods for measuring and counting the number of atoms, molecules, formula units, and ions in samples of diff erent chemicals?

Procedure

1. Read through this Procedure, and create a table you can use to record your results for each step.

2. Measure the mass of a candle. Light the candle, and burn the paraffi n wax for 10 min. Put out the candle, and let it sit for 4 min to allow the melted wax to solidify. Measure the mass of the candle again.

3. Measure the mass of a paper clip. Try fl oating the paper clip on water in a beaker. Hold the paper clip horizontally (fl at). Very carefully, lower the paper clip onto the surface of the water. Th e paper clip should fl oat.

4. Measure the mass of a 10 mL graduated cylinder. Using a dropper full of water, count the number of drops of water you need to get 1 mL of water in the cylinder. Measure the mass of the water and the cylinder.

5. a. Calculate the mass of 0.10 mol of sodium chloride. Using weighing paper, measure the mass on a balance, and place it in a 50 mL graduated cylinder. Measure and record the volume of the salt. Return the salt to the weighing paper.

b. Calculate the mass of 0.10 mol of sucrose. Using weighing paper, measure the mass, and place it in the 50 mL graduated cylinder. Measure and record the volume of the sugar. Return the sugar to the weighing paper.

6. a. Draw a 10 cm by 10 cm square on a piece of paper. Measure the mass of your favourite colour of wax crayon.

b. Colour in the entire square as completely as possible with the wax crayon. Measure the mass of the crayon again.

c. Repeat the process with a 20 cm by 20 cm square on a piece of paper.

5-B

246 MHR • Unit 3 Quantities in Chemical Reactions


Analyze and Interpret

1. Refer to your results from Procedure step 2 to answer this question.

a. Calculate the number of wax molecules that burned. Assume that the formula for paraffi n wax is C25H52(s).

b. Calculate the number of carbon atoms that burned. 2. Refer to your results from Procedure step 3 to answer

this question: How many atoms of iron is the water holding up? Assume that the paper clip is pure iron.


a. What is the mass of 1 mL of water? b. How many water molecules are in 1 mL of water? c. How many hydrogen atoms are in one drop of water? d. Calculate the volume of one mole of water.


a. Compare the volumes of the 0.10 mol samples of table salt and table sugar, and account for any diff erences.

b. How many sodium and chloride ions are in the salt sample?

c. How many oxygen atoms are in the sugar sample? 5. Refer to your results from Procedure step 6 to answer

this question. Assume that the wax crayon, like the candle, is paraffi n wax. Based on the mass of wax crayon used, calculate the number of molecules of wax in the 10 cm by 10 cm square and the 20 cm by 20 cm square. Compare the diff erence in the areas of the two squares with the diff erence in the masses of the wax. How do they compare?

Conclude and Communicate

6. When burning a candle like the one in this investigation, how long would it take to burn 1 mol of paraffi n wax?

7. In terms of the wax crayon, what would the dimensions of a square coloured on a page have to be to use an entire mole of wax?

8. Calculate the mass of one mole of water. Th en, using your calculations for the volume of one mole of water, calculate the density of water at room temperature in grams per millilitre (g/mL). Check a reference source to see if this value is reasonable.

Extend Further

9. INQUIRY Design an investigation to determine the number of particles (molecules or formula units) of chalk it would take to write your name. First, research the main chemical that makes up chalk. Perform your investigation aft er your teacher approves it.

10. RESEARCH In this investigation, you assumed that the formula for the paraffi n wax you used was C25H52(s). Research the diff erent formulas for paraffi n wax. How did the formula you used aff ect your results? Why was it important to make an assumption about the formula in order to calculate your results?

Chapter 5 The Mole: A Chemist’s Counter • MHR 247


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