# The Mole

## Unit Plan

### Objectives

In this unit, students learn about the concept of the mole and how it is used in chemistry. Students will:

• apply the mole concept to representative particles.
• perform conversions between moles, representative particles, mass, and volume.
• solve stoichiometry problems, given balanced equations.
• prepare molar solutions in the laboratory.

### Related Materials & Resources

The possible inclusion of commercial websites below is not an implied endorsement of their products, which are not free, and are not required for this lesson plan.

http://www.learner.org/vod/vod_window.html?pid=803

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# Multiple-Choice Items:

1.      What is the molar mass of ethyl chloride, C2H5Cl, in grams per mole?

 A 48.5 B 52.5 C 60.5 D 64.5

2.      The balanced equation below shows the reaction of propane (C3H8) with oxygen to yield carbon dioxide and water. How many moles of carbon dioxide can be produced from 2 moles of propane?

C3H8 + 5O2 → 3CO2 + 4 H2O

 A 1 B 3 C 6 D 9

3.      What is the mass of 1.3 moles of aluminum?

 A 0.037 g B 26.98 g C 35.07 g D 6.02 × 1023 g

4.      200 g N2O = __?__ molecules N2O

 A 4.55 B 44.0 C 2.74 × 1024 D 1.20 × 1026

5.      In the reaction shown by the balanced equation below, if 360.4 grams of water are produced, how many moles of H2 are required?

2H2 + O2 → 2H2O

 A 1 mol H2 B 2 mol H2 C 10 mol H2 D 20 mol H2

6.      In the reaction shown by the balanced equation below, 18.02 grams of water are produced, all of the silane (SiH4) is used up, and oxygen is still available after the reaction. Which compound is the limiting reagent?

SiH4 + 2O2 → SiO2 + 2H2O

 A SiH4 B O2 C SiO2 D H2O

7.      Which statement best describes molarity?

 A Molarity is the number of moles of solute per liter of solvent. B Molarity is the number of moles of solute per liter of solution. C Molarity is the weight of the solute divided by the molecular weight. D Molarity is the molecular weight divided by the weight of the solute.

8.      How many grams of nitric acid are present in 1.0 L of a 1.0 M HNO3 solution?

 A 0.016 g B 31.02 g C 63.02 g D 93.06 g

9.      What is the molarity of a solution containing 87.8 g NaCl in 3.0 liters of solution?

 A 0.5 M B 1.5 M C 2.0 M D 4.5 M

 1. D 2. C 3. C 4. C 5. D 6. A 7. B 8. C 9. A

10.  How many grams of KNO3 would be needed to prepare 1.00 liter of a 1.5 M solution of KNO3? Show your work and label the units. Circle your answer.

11.  Make a list of the steps required to measure two moles of potassium chloride, KCl, in the laboratory. Potassium chloride is a white powder at room temperature. Make sure to label all units.

# Short-Answer Key and Scoring Rubrics:

10.  How many grams of KNO3 would be needed to prepare 1.00 liter of a 1.5 M solution of KNO3? Show your work and label the units. Circle your answer.

 Points Description 2 Student correctly calculates the number of grams of KNO3 needed to prepare the solution. Solution: M = mol/L 1.5 M = mol/1 L Molecular weight of KNO3 is 39.10 + 14.01 + 16.00(3) = 101.11 g/mol 1.5 mol× 101.11 g KNO3 /mol = 151.7 g KNO3 Shows all steps in the calculation. Labels all units. 1 Student correctly calculates the number of grams of KNO3 needed to prepare the solution. Solution: M = mol/L 1.5 M = mol/1 L Molecular weight of KNO3 is 39.10 + 14.01 + 16.00(3) = 101.11 g/mol 1.5 mol× 101.11 g KNO3/mol = 151.7 g KNO3 Does not show one or more steps in the calculation. Does not label all units. 0 Student does not correctly calculate the number of grams of KNO3: Does not show most of the steps in the calculation. Does not label most units.

11.  Make a list of the steps required to measure two moles of potassium chloride, KCl, in the laboratory. Potassium chloride is a white powder at room temperature. Make sure to label all units.

 Points Description 2 Student lists all of the steps required to measure two moles of KCl in the correct order: 1. Determine the molecular mass of KCl. 2. Determine the mass of KCl in two moles. 3. Measure the mass of KCl. Student correctly calculates the molecular mass of KCl: 39.10 + 35.45 = 74.55 g/mol. Student correctly calculates the mass of KCl in two moles: 74.55 × 2 = 149.1 g. 1 Student lists all of the steps required to measure two moles of KCl, in the correct order: 1. Determine the molecular mass of KCl. 2. Determine the mass of KCl in two moles. 3. Measure the mass of KCl. Student incorrectly calculates either the molecular mass of KCl or the mass of KCl in two moles. 0 Student does not list all of the steps required to measure two moles of KCl, or the steps are out of order. Student’s calculations of both the molecular mass of KCl and the mass of KCl in two moles are incorrect.

# Performance Assessment:

Hand out copies of The Mole: Student Worksheet (S-C-8_Performance Assessment Worksheet.doc) to use for both Parts 1 and 2.

Part 1: Measuring a Mole

Give each student a sample of copper, nickel, tin, aluminum, or silicon, and ask him/her to measure out a mole of the element. Provide student with a balance, a metric ruler, a periodic table, weighing paper, and a spatula to work with. Have the student measure out the mole, show you the mole as it sits on the balance, and then write a brief description of the method used. The description should include the steps used, the mass of a mole of the element, and the number of atoms in one mole of the substance. All units should be labeled.

Part 2: Preparing a Molar Solution

Have student prepare 500 milliliters of a 0.5 molar solution of sodium chloride (table salt). Provide student with a volumetric flask, sodium chloride, distilled water, a balance, and weighing paper. Have student prepare the solution, show it to you in the volumetric flask, and then write a brief description of the method used. The description should include the steps used, the amounts of sodium chloride and water used, and an explanation of how chemists use molarity in the laboratory. All units should be labeled.

# Performance Assessment Scoring Rubric:

 Points Description 5 The student completes all five of the requirements: correctly measures one mole of a given element. description of the method includes: the steps used, the mass of a mole of the element, and the number of atoms in one mole of the substance. correctly prepares 500 mL of a 0.5 M solution of NaCl. description of the method includes: the steps used, the amounts of sodium chloride and water, and a definition of molarity. all units labeled in the calculations for both parts. 4 The student completes four of the requirements. 3 The student completes three of the requirements. 2 The student completes two of the requirements. 1 The student completes one of the requirements. 0 The student demonstrates lack of understanding or does not attempt to complete the assessment.

DRAFT 06/01/2011 