10.2 Lesson 10.2 Mole-Mass and Mole-Volume Relationship
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10.2.1 Describe how to convert the mass of a substance to the number of moles of a substance, and moles to mass. 10.2.2 Convert the volume of a gas at STP to the number of moles of the gas.
Lesson Links 10.2 Kinetic Art: The Mole Map Ch. 10 Lab 12: The Masses of Equal Volumes of Gases Ch. 10 Lab 13: Empirical Formula Determination Ch. 10 Core TR: Section 2 Review 10.2 Lesson Overview (PowerPoint file) 10.2 Chemistry Tutorial: Converting Moles to Mass and Mass to Moles Chapter 10 Online Student Edition Study WB Chapter 10 Lesson 2
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Overview
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In this lesson you will cover conversions between the mass of a substance and the amount of the substance in moles using the molar mass as a conversion factor. You will also cover conversions between the volume of a gas at STP and the amount of the gas in moles. Classroom Materials The Mole-Volume Relationship: dry ice, towel, hammer, large plastic bag, duct tape, tongs, beaker, balance Focus on ELL: three 100 mL beakers, 50 mL each of pennies, dimes, and quarters
Standard There are no items.
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Chemistry & You Description Engage
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Pacing Chapter 10 Online Student Edition
Have students read the Chemistry & You text on p. 317 and examine the accompanying photograph. Ask What method, other than estimating the volume of each individual penny, might you use to determine the number of pennies present? (Sample answer: Divide the total mass of all the pennies by the mass of one penny.)
Activate Prior Knowledge Description Engage
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Review the mathematical conversion of moles to number of particles and number of particles to moles from p. 309-311. Stress that using dimensional analysis in problem solving allows students to perform these calculations without having to memorize the process. Emphasize the use of writing units when solving problems.
The Mole-Mass Relationship Description Explain Explain that in chemical manufacturing processes, reactants are purchased by mass, and products are sold by mass. However, point out that processes are set up and designed based on the ratio in which moles of reactants combine with each other to form moles of products. Ask If one mole of reactant produces one mole of product, predict how you can find the mass of product if you know the mass of the reactant. (Convert the mass of reactant to number of moles. Then, convert that number of moles to the mass of product.) Tell students that they will learn more about conversions such as this in Chapter 12.
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The Mole-Mass Relationship Description Explain Have students examine the problem-solving process for Sample Problems 10.5 and 10.6 on pages 318 and 319. Have students create a T-chart to compare and contrast the process for converting between moles to mass and mass to moles. Have students write a "caution" sticky note listing what to look for, what mistakes to avoid, and what process to follow in these types of problems. Tell students to place the sticky note in the text near these sample problems.
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Chapter 10 Online Student Edition
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10.2 Chemistry Tutorial: Converting Moles to Mass and Mass to Moles
Have students complete the 10.2 Chemistry Tutorial: Converting Moles to Mass and Mass to Moles on PearsonChem.com.
The Mole-Mass Relationship Description
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Extend The dalton, abbreviated Da, is frequently used as a unit of molar mass in biochemistry. One dalton is equal to one gram per mol (1Da = 1 g/mol).
The Mole-Volume Relationship Description Explain Ask students to name the unit that is used for the mass of a mole. (grams per mole, g/ mol) Ask What unit is used for the volume of a mole? (liters per mole, L/mol) Point out that, unlike solids and liquids, the molar volume of gases is predictable, but can be affected by temperature and pressure.
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Ask How does temperature affect the volume of a gas? (When temperature increases, volume increases. When temperature decreases, volume decreases.) Ask How does pressure affect the volume of a gas? (When pressure increases, volume decreases. A decrease in pressure causes an increase in volume.) Emphasize that when comparing the molar volume of gases, it is necessary to have the gases at the same conditions of temperature and pressure.
The Mole-Volume Relationship Description
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Explore Use a teacher demonstration to allow students to observe an approximation of molar volume. Wrap dry ice in a towel and hit it with a hammer until it is in small pieces. Place 44 g (1 mol CO2) of the small pieces in a beaker. Expel any air from a plastic bag, and tape the opening of the bag securely over the top of the beaker. As the dry ice sublimes, the bag will inflate. The volume of gas produced will not equal 22.4 L because conditions are not standard. However, the volume will be close to this value. Materials: dry ice, towel, hammer, large plastic bag, duct tape, tongs, beaker, balance
The Mole-Volume Relationship Description Explain Review the concept of density as a ratio of mass to volume. Discuss the units of measure that correspond to density. (g/mL, g/cm3, or g/L) Ask If you had one mole of gas at STP, how could you calculate the density? (Divide the number of grams of gas in one mole by 22.4 L.)
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Emphasize that if the number of moles is given, the mass of the substance or the volume of a gas can be calculated. This concept will continue to be essential as students study mass-mass and other stoichiometric relationships in Chapter 12.
The Mole-Volume Relationship Description Explain Have students study Figure 10.8. Guide them through examples of the various mole conversions. For example, start with 50.0 g of a compound or element and covert it to moles, and then to particles. Then, start with a given volume of a gas and convert it to mass or particles. Have students recreate this roadmap in a visual way that helps them to clearly see the various relationships. Encourage students to use their visual as a reference when attempting to do homework problems.
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10.2 Kinetic Art: The Mole Map
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Figure 10.8
Have students complete the 10.2 Kinetic Art: The Mole Map on PearsonChem.com.
The Mole-Volume Relationship Description
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Extend Ask students if they can determine the volume of 1 mol of air at STP. Students should correctly identify the volume as 22.4 L. Remind students that air is a mixture of gases.
Assess and Remediate Description Evaluate Have students solve problems in which they use or explain the conversions for converting mass or volume to moles. Ask volunteers to come to the board to show their calculations. Have the class determine whether the calculations are correct.
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Chapter 10 Online Student Edition
Then have students complete the 10.2 Lesson Check. Remediate Review the concept of density as a ratio of mass to volume. Ask If you know the molar volume of a gas, how could density help you determine the molar mass? (Molar mass is the product of density and molar volume.)
Differentiated Instruction Description Struggling Students Students may not understand the difference between moles and mass. Explain that in the types of problems shown in Sample Problems 10.5 and 10.6 on pages 318 and 3 19, mass is typically given in grams. Moles is the unit of measurement for the number of representative particles. Clearly emphasize that mass is not equivalent to moles. Suggest that students create a spider chart to explore the relationship between the mole, mass, volume, and number of particles.
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Chapter 10 Online Student Edition
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Figure 10.8
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Study WB Chapter 10 Lesson 2
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Ch. 10 Core TR: Section 2 Review
Special Needs Students To help students with conversion problems, have them write each of the three pairs of conversion factors in Figure 10.8 on the two sides of an index card. Then have students create individual cards with each of the units of the known and unknown quantities: grams, moles, liters, and representative particles. Students can use the cards to model a problem as a method of testing their choices of conversion factors before solving the problem. Advanced Students Have students apply their problem-solving skills to this question: Salvatore heated a mixture of potassium chlorate and manganese dioxide, producing 0.377 L of oxygen gas at STP. What was the mass of the gas collected? (0.539 g)
Focus on ELL Description
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Frontload the Lesson
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Study WB Chapter 10 Lesson 2
Place three 100 mL beakers on a table. To the first beaker, add 50 mL of pennies. Repeat with the remaining beakers, using dimes for one and quarters for the other. Ask students to identify the similarities and differences of each beaker. Have them predict how this demonstration might relate to the topics in this lesson.
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Ch. 10 Core TR: Section 2 Review
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Homework
