Materials Included In Kit

Additional Materials Required

Safety Precautions

The materials in this kit are considered nonhazardous and are reusable. Follow all classroom or laboratory safety guidelines.

Disposal

The mole concept puzzle may be stored for reuse. After determining if the puzzle sheets will be cut, instruct students on proper storage. If the sheets will be cut, use resealable bags or envelopes to keep the puzzle pieces organized together and tidy.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab or at the beginning of the class.
• After students have completed the mole concept puzzle questions, they need to organize the information on the reverse sides. The answers must be arranged in numerical order from lowest to highest to obtain the correct clues.
• The easiest way to do this is for students to cut out the squares, arrange them in numerical order and then flip them over to get the proper arrangement of letters, spaces, and punctuation.|The students may also systematically work through the puzzle clues and then note the answers lowest to highest, writing down the information as they go. This eliminates the cutting and physical manipulation and the extra step of ordering the puzzle clues 1–16.
• The instructor should let students know how each group will relay their information to the rest of the class. For example, are students going to cut out each square and tape it onto a board or wall in the proper order to arrive at the quote, or are students going to write their section on the board and then each subsequent group will do the same?
• Before beginning the activity, copy the Mole Concept Puzzle Sheets so you will have extra copies in case of loss.
• A small amount of liberty was taken with the quote. The original quote is “When we attempt to conceive the number of particles in an atmosphere [gas], it is somewhat like attempting to conceive the number of stars in the universe; we are confounded with the thought. But if we limit the subject, by taking a given volume of any gas, we seem persuaded that... the number of particles must be finite.”

Teacher Tips

• This activity is appropriate for studying the idea of mole concepts, molar mass, and Avogadro’s number.
• The Mole Concept Puzzle Sheets can be used while learning the material or as a review.
• Each puzzle sheet follows the same basic template, thus all are the same level of difficulty.

Answers to Prelab Questions

1. Iron
   1. Write the chemical symbol. Fe
   2. What is the molar mass of iron? 55.85 g/mol
   3. Calculate the mass of 8.23 x 10²³ atoms of iron.
      {12280_PreLabAnswers_Equation_1}
   4. Calculate the moles of 8.23 x 10²³ atoms of iron.
      {12280_PreLabAnswers_Equation_2}
2. Barium nitrate
   1. Write the chemical formula. Ba(NO₃)₂
   2. Calculate the molar mass.
      {12280_PreLabAnswers_Equation_3}
   3. Determine the moles present in 129.04 g of barium nitrate
      {12280_PreLabAnswers_Equation_4}
3. Carbon dioxide
   1. Write the chemical formula. CO₂
   2. Calculate the molar mass
      {12280_PreLabAnswers_Equation_5}
   3. Calculate the molecules of carbon dioxide in 62.34 g of carbon dioxide.
      {12280_PreLabAnswers_Equation_6}
   4. Calculate the moles of carbon dioxide in 62.34 g of carbon dioxide.
      {12280_PreLabAnswers_Equation_7}

Answers to Questions

Mole Concept Quote

“When we attempt to conceive the number of particles in an atmosphere of gas, it is like attempting to conceive the number of stars in the universe; we are confounded with the thought. But if we limit the subject, by taking a given volume of gas, the number of particles must be finite.”

Teacher Handouts

12280_Teacher1.pdf

12280_Teacher2.pdf

Introduction

What is a mole? The dictionary defines a mole as “a small, insectivorous, burrowing mammal having a thickset body with silky light-brown to dark-gray fur, rudimentary eyes, tough muzzles and strong forefeet for digging and usually living underground.” Another definition of a mole is “a small growth on the human skin.” The term “mole” also has great significance in chemistry. A molecular mole represents a unit of measure that is a collection of 6.022 x 10²³ particles. The dictionary defines this type of mole as “the amount of a substance that has a weight in grams equal to the substance’s molecular weight.” Clue in to mole concepts with this puzzle activity and then join efforts with the whole class to decode a mole message.

Concepts

• Mole concept
• Molar mass
• Stoichiometry
• Avogadro’s number

Background

The mole concept is fundamental to chemistry. It is the bridge that allows us to cross over from the macroscopic world in which we live to the submicroscopic world of atoms and molecules. Understanding the mole concept makes it possible to analyze compounds and determine their chemical formulas—to study the composition of matter. Applying the mole concept makes it possible to relate the amounts of chemicals consumed and produced in chemical reactions—to study the properties of matter. To study the properties of matter one must first start with the building blocks of matter—atoms.

Atoms may be invisible, immeasurably small, infinitesimal in size—but they are finite. As finite particles, atoms must have real properties. All atoms of a given element have the same atomic mass. Atoms of different elements have different atomic masses. These statements—the cornerstone of Dalton’s atomic theory—provided a starting point for calculating relative atomic masses of atoms based on the mass percentage of elements in compounds. There was still a long way to go, however, before Dalton’s suggestion of actually counting atoms would be possible.

In 1811, Amedeo Avogadro, an obscure Italian chemistry professor, published a stunning hypothesis—that equal volumes of gases at equal pressures and temperatures contain equal numbers of atoms or molecules. This hypothesis was so stunning that it was completely ignored for more than 50 years. It was not until many years after Avogadro’s death that his hypothesis became enshrined as a law and acquired a numerical value to go along with it. Avogadro’s number is defined as the number of representative particles (atoms or molecules) contained in a specified mass, called the molar mass, of any pure substance. For the purposes of this activity, four significant figures will be used—6.022 x 10²³ particles/mole.

The average atomic mass of atoms and Avogadro’s number are routinely used today by chemists all over the world to count both atoms and molecules—chemists count atoms by weighing them. “Counting by weighing” makes it possible to analyze compounds found in nature and synthesize new compounds in the lab (see Figure 1). {12280_Background_Figure_1_Molar coversions} One mole of a pure substance contains 6.022 x 10²³ particles (e.g., molecules, atoms) and has a mass equal to the sum of atomic weights of all elements in the formula.

The molar mass is the mass of one mole of the specified substance. The molar mass is calculated by adding up the average atomic masses of the components. If the substance is an element, the molar mass is simply the average atomic mass found on the periodic table in units of grams. If the substance is a compound, the molar mass is calculated by adding the average atomic mass of each atom multiplied by the number of atoms in the chemical formula for the compound.

Example 1: What is the molar mass of copper to four significant figures?

63.55 g/mol (found on the periodic table)

Example 2: What is the molar mass of aluminum chloride?

Write the correct formula for ionic compound containing Al³⁺ and Cl^– ions AlCl₃

Molar mass (AlCl₃) =

Al: (1   26.98) = 26.98 g
Cl: (3   35.45) = 106.4 g
Sum = 133.4 g/mole of AlCl₃

Example 3: What is the molar mass of aluminum sulfate?

Write the correct formula for ionic compound containing Al³⁺ and SO₄^2– ions Al₂(SO₄)₃

Molar mass (Al₂(SO₄)₃ = Al₂(SO₄)₃

Al: (2   26.98) = 53.96 g
S: (3   32.07) = 96.21 g
O: (12   16.00) = 192.0 g
Sum = 342.2 g/mole of Al₂(SO₄)₃

Experiment Overview

The purpose of this cooperative class activity is to answer a series of mole concept problems on a puzzle sheet and use the answers to decode a historical quote from John Dalton describing his approach to the theory of atoms. There are 15 different puzzle sheets, Sets 1–15, each with 16 unique puzzle pieces (questions) that have number answers. After each group has verified their answers, the puzzle pieces may be cut out and arranged in numerical order from lowest to highest. The reverse side of each puzzle piece has a clue, which may be a letter, punctuation mark, or blank. (Blanks correspond to spaces after punctuation marks.) The whole class works together to enter their clues in the correct order and sequence and to solve the puzzle!

Prelab Questions

1. Iron
   1. Write the chemical symbol.
   2. What is the molar mass of iron?
   3. Calculate the mass of 8.23 x 10²³ atoms of iron.
   4. Calculate the moles of 8.23 x 10²³ atoms of iron.
2. Barium nitrate
   1. Write the chemical formula.
   2. Calculate the molar mass.
   3. Determine the moles present in 129.04 g of barium nitrate
3. Carbon dioxide
   1. Write the chemical formula.
   2. Calculate the molar mass.
   3. Calculate the molecules of carbon dioxide in 62.34 g of carbon dioxide.
   4. Calculate the moles of carbon dioxide in 62.34 g of carbon dioxide.

Safety Precautions

The materials in this kit are considered nonhazardous and are reusable. Follow all classroom or laboratory safety guidelines.

Procedure

1. Divide the class into 15 groups.
2. Each group receives a unique Mole Concept Puzzle Sheet.
3. Working within your group, answer all 16 puzzle questions on the puzzle sheet to three significant numbers.
4. After verifying the answers with your teammates, cut out the individual puzzle pieces and arrange them in order from lowest to highest numerical values based on the answers to the puzzle questions. Note: If desired, this step may be omitted and the puzzle decoded without cutting the puzzle sheets. See step 7.
5. Each box on the reverse side of the puzzle sheets has a letter, punctuation mark or is blank. Turn over the pieces in order and write the clues in the spaces provided on the Puzzle Quote Sheet (see the Set No. for your puzzle sheet).
6. All 15 groups should report their clues in order, from set 1 through set 15, to the whole class. The result is a profound quote about the beginning of the mole concept!
7. (Optional) After verifying the answers with your teammates, rank each puzzle, 1–16, in order from lowest to highest numerical values based on the puzzle answers. Transfer the corresponding clues on the Mole Concept Puzzle Quote Sheet without cutting.

Student Worksheet PDF

12280_Student1.pdf