Balancing Chemical Equations

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)

Balancing Chemical Equations

PART I:

Background Information: Word and Formula Equations

The first step in writing a chemical equation is to identify the facts to be represented. It is helpful to write a word equation, an equation in which the reactants (left) and products (right) in a chemical reaction are represented by words. A word equation has only qualitative (descriptive) meaning. It does not give the whole story because it does not give the quantities of reactants used or products formed. A formula equation represents the reactants (left) and products (right) of a chemical reaction by their symbols or formulas. Chemical formulas must be written

correctly according to the rules of nomenclature.

Word Equation (A)

An aqueous solution of hydrochloric acid reacts with an aqueous solution of sodium hydroxide to produce liquid water and aqueous sodium chloride.

Formula Equation (A)

HCl (aq) + NaOH (aq) H2O (l) + NaCl (aq)

Word Equation (B)

Solid calcium carbonate decomposes when heated to yield solid calcium oxide and carbon dioxide gas.

Formula Equation (B)

CaCO3 (s) CaO (s) + CO2 (g)

Word Equation (C)

Gaseous ethene and gaseous hydrogen will react in the presence of a platinum catalyst to form ethane gas.

Formula Equation (C)

C2H4 (g) + H2 (g)

Pt

C2H6 (g)

Group Activity:

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 2. What do the following symbols in the equations above represent?

(s) (l)

(g) (aq)

Pt

3. In the table below, indicate the reactant(s) and product(s) for each of the equations above.

REACTANTS PRODUCTS EQUATION

Name Formula Name Formula A

B

C

4. In chemical equation (C), is platinum a reactant, a product, or neither? Explain.

Model: Atoms Are Conserved in Chemical Reactions.

Chemical reactions are described by chemical equations. According to the Law of Conservation of Mass (Matter), atoms are neither created nor destroyed when chemical reactions take place. Therefore, the number of atoms of each element must be identical on the reactant (left) and the product (right) sides of a balanced chemical reaction.

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Reaction (D) CuO (s) + H2(g) Cu(s) + H2O(g)

+ +

Reaction (E) CO(g) + O2(g) CO2(g)

+

Group Activity:

5. How many of each type of atom are represented on each side of the equation in reaction (D)?

Cu O H

Reactant Side Product

Side

6. Does this equation (D) obey the Law of Conservation of Mass (Matter)? Explain.

7. How many of each type of atom are represented on each side of the equation in reaction (E)?

C O

Reactant Side Product

Side

8. Does this equation (E) obey the Law of Conservation of Mass (Matter)? Explain.

9. If either Reaction D or E does not obey the Law of Conservation of Mass (Matter), draw additional molecules on the reactant and/or product side in order to make the number of all atoms equal on both sides of the equation. (Remember that once written correctly, chemical formulas cannot be changed. In other words, molecules must remain intact.)

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 10.In reaction (D), how many H2O molecules are produced for every H2molecule that is

consumed?

11.In reaction (E), how many CO2 molecules are produced for every O2 molecule consumed?

12.In reaction (E), how many CO molecules react with every O2 molecule?

Independent Activity:

1. Read pages 243 through 248.

2. Write word and formula equations for the chemical reaction that occurs when solid sodium oxide is added to water at room temperature and forms sodium hydroxide (dissolved in the water). Include symbols for physical states in the formula equation.

3. Translate the following chemical equation into a sentence:

PbCl2(aq) + Na2CrO4(aq) PbCrO4(s) + NaCl(aq)

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Balancing Chemical Equations

PART II:

Background Information: Balanced Chemical Equations

A balanced chemical equation represents a chemical reaction that obeys the Law of Conservation of Mass (Matter). It can be thought of as describing how many atoms or molecules of reactants are consumed in order to produce a certain number of atoms or molecules of

products. A coefficient is a small whole number that appears in front of a formula in a chemical equation. The coefficient represents the relative number of atoms or molecules.

Recall from Part I of this activity the following reactions:

Reaction (D) CuO (s) + H2(g) Cu(s) + H2O(g)

+ +

Reaction (E) CO(g) + O2(g) CO2(g)

+

In order to answer question 9, Reaction D was already drawn correctly, but Reaction E should have been redrawn as pictured below:

+

This picture shows 2 carbon atoms and 4 oxygen atoms on each side of the equation. These atoms are represented as 2 CO molecules and 1 O2 molecule on the reactant side and 2 CO2

molecules on the product side of the equation.

Group Activity:

1. Based on the correct drawings write a formula equation that will obey the Law of

Conservation of Mass (Matter) for both Reaction D and E. In order to do this, coefficients may be required.

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 2. Is the number of molecules identical on the reactant and product sides of both of these

balanced equations?

3. Explain how your answer to # 2 can be consistent with the idea that atoms are neither created nor destroyed when chemical reactions take place.

4. Why must we balance chemical equations?

Model: Balanced Chemical Equations

a) Zn (s) + 2 HCl (aq) H2 (g) + ZnCl2 (aq)

b) 2 H2 (g) + O2 (g) 2 H2O (g)

c) BaCl2 (aq) + 2 AgNO3 (aq) Ba(NO3)2 (aq) + 2 AgCl (s)

d) 2 C6H14 (g) + 19 O2 (g) 12 CO2 (g) + 14 H2O (g)

Group Activity:

5. What is the coefficient for hydrochloric acid in equation a?

6. What is the coefficient for barium nitrate in equation c?

7. How many barium nitrates are on the product side of equation c? Does your answer agree with your answer for # 6 above?

8. How many barium atoms are on each side of equation c? Explain how you arrived at this answer.

9. How many carbon atoms are on each side of equation d? Explain how you arrived at this answer.

10.How many oxygen atoms are on each side of equation d? Explain how you arrived at this answer.

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 11.Balance the following chemical equations:

a) ______Cr(s) + ______S8(s) ______Cr2S3(s)

b) ______NaHCO3 (s) ______Na2CO3 (s) + ______CO2(g) + ______H2O (g)

c) ______Fe2S3 (s) + ______HCl (g) ______FeCl3 (s) + ______H2S (g)

d) ______CS2 (l) + ______NH3 (g) ______H2S (g) + ______NH4SCN (s)

e) ______Fe2(SO4)3 (aq) + _____KOH (aq) ______K2SO4 (aq) + ______Fe(OH)3 (s)

f) ______C25H52 (l) + ______O2 (g) ______CO2(g) + ______H2O (g)

12. The trial-and-error method for balancing equations can be successful; however it can be made easier by following some simple guidelines. Develop a few simple guidelines to achieve a balanced chemical equation.

13.Use your guidelines to balance the following chemical equations: a) _____H3PO4 _____H4P2O7 + _____H2O

b) _____C6H6 + _____O2 _____CO2 + _____H2O

c) _____Al(OH)3 + _____H2SO4 _____Al2(SO4)3 + _____H2O

14.What adjustments, if any, need to be made to your guidelines in order to balance the equations above?

Independent Activity:

15.Read pages 250 through 254. Carefully study the sample problems 8.3, 8.4, and 8.5 on pages 252 – 254.

16.Work practice problem on page 254.

17.Write the balanced chemical equation for the gaseous reaction of methane (CH4) with oxygen

(O2) to form carbon dioxide (CO2) and water (H2O).

18.Chapter 8: page 270, questions #20 and #21. 19.Chapter 8: page 272, questions #41 and #47.

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Balancing Chemical Equations Teacher Notes

Time Required:

Estimated 20-30 minutes for Part I and 50 minutes for Part II. It is suggested that Part I and Part II be completed on consecutive days.

Prerequisites:

Chemical formulas and nomenclature

Learning Objectives:

1. Write word equations correctly.

2. Write formula equations correctly, using proper symbolic notation. 3. Correctly balance chemical equations.

4. Explain how a balanced chemical equation illustrates the Law of Conservation of Mass (Matter).

Considerations:

This activity is a wonderful way to introduce the concept of writing and balancing chemical equations.

Be careful not to answer the students’ questions for them. If a group asks a question concerning content, rather than supplying the answer, ask a question in return that will steer them toward discovering the answer for themselves. Another way to intervene with the group may be to have the Spokesperson or Presenter for the group to restate their reasoning so that they have the opportunity to pinpoint misconceptions or faulty reasoning on their own.

Closure:

It is always good to have the students reflect on what they have learned before leaving class. One way to do this is to stop the activity about 5 minutes before the end of class and have students take out a sheet of paper. Have them record one thing that they learned as a result of the lesson that day. Then have them to ask a question concerning the lesson. The question could be something that is still unclear to them or it could be something they are curious about or a subject that they think may be related to the lesson.

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Answers to Questions in Group Activity: Part I:

1. What does the arrow represent in a chemical equation? Yields or produces

2. What do the following symbols in the equations above represent?

(s) solid (l) liquid

(g) gas (aq) aqueous

heat Pt platinum catalyst

3. In the table below, indicate the reactant(s) and product(s) for each of the equations above.

REACTANTS PRODUCTS EQUATION

Name Formula Name Formula

A hydrochloric acid HCl water H2O

sodium hydroxide NaOH sodium chloride NaCl

B calcium

carbonate

CaCO3 calcium oxide CaO

carbon dioxide CO2

C ethene C2H4 ethane C2H6

hydrogen H2

4. In chemical equation (C), is platinum a reactant, a product, or neither? Explain.

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5. How many of each type of atom are represented on each side of the equation in reaction (D)?

Cu O H

Reactant Side

1 1 2

Product Side

1 1 2

6. Does this equation (D) obey the Law of Conservation of Mass (Matter)? Explain.

Yes, because there are the same number of each atom on both sides of the equation.

7. How many of each type of atom are represented on each side of the equation in reaction (E)?

C O

Reactant Side

1 3

Product Side

1 2

8. Does this equation (E) obey the Law of Conservation of Mass (Matter)? Explain.

No, because there are NOT the same number of oxygen atoms on each side of the equation.

9. If either Reaction D or E does not obey the Law of Conservation of Mass (Matter), draw additional molecules on the reactant and/or product side in order to make the number of all atoms equal on both sides of the equation. (Remember that once written correctly, chemical formulas cannot be changed. In other words, molecules must remain intact.)

+

10.In reaction (D), how many H2O molecules are produced for every H2molecule that is

consumed?

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 11.In reaction (E), how many CO2 molecules are produced for every O2 molecule consumed?

two

12.In reaction (E), how many CO molecules react with every O2 molecule?

two Part II

1. Based on the correct drawings write a formula equation that will obey the Law of

Conservation of Mass (Matter) for both Reaction D and E. In order to do this, coefficients may be required.

(D) CuO (s) + H2(g) Cu(s) + H2O(g) already balanced

(E) 2 CO(g) + O2(g) 2 CO2(g)

2. Is the number of molecules identical on the reactant and product sides of both of these balanced equations?

No!!!!!!! NOTE: This question asks about molecules, not atoms. In reaction (D), there are 2 molecules on the reactant side and 1 atom and 1 molecule on the product side. In reaction (E), there are 3 molecules on the reactant side and 2 molecules on the product side. If your students do not see this, hint that they look back at their picture from part I.

3. Explain how your answer to # 2 can be consistent with the idea that atoms are neither created nor destroyed when chemical reactions take place.

Because the atoms are balanced, even though the molecules are not.

4. Why must we balance chemical equations?

In order to obey the Law of Conservation of Mass (Matter). 5. What is the coefficient for hydrochloric acid in equation a? 2 6. What is the coefficient for barium nitrate in equation c? 1

7. How many barium nitrates are on the product side of equation c? Does your answer agree with your answer for # 6 above? 1, yes

8. How many barium atoms are on each side of equation c? Explain how you arrived at this answer. 1, because there is 1 Ba in BaCl2 and 1 Ba in Ba(NO3)2

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 9. How many carbon atoms are on each side of equation d? Explain how you arrived at this

answer. 12, because there are 2 molecules of C6H14 and 12 molecules of CO2

10.How many oxygen atoms are on each side of equation d? Explain how you arrived at this answer. 38, because there are 19 molecules of O2, 12 molecules of CO2 = 24 atoms of O, and

14 molecules of H2O = 14 atoms of O

11.Balance the following chemical equations:

a) ___16___Cr(s) + ___3___S8(s) ___8___Cr2S3(s)

b) ____2__NaHCO3 (s) ______Na2CO3 (s) + ______CO2 (g) + ______H2O (g)

c) ______Fe2S3 (s) + ____6__HCl (g) __2____FeCl3 (s) + ___3___H2S (g)

d) ______CS2 (l) + ___2___NH3 (g) ______H2S (g) + ______NH4SCN (s)

e) ______Fe2(SO4)3 (aq) + __6__KOH (aq) ___3__K2SO4 (aq) + __2___Fe(OH)3 (s)

f) ______C25H52 (l) + ___38___O2 (g) __25____CO2(g) + ___26___H2O (g)

12. The trial-and-error method for balancing equations can be successful; however it can be made easier by following some simple guidelines. Develop a few simple guidelines to achieve a balanced chemical equation.

Student answers may vary.

13.Use your guidelines to balance the following chemical equations: a) __2__H3PO4 _____H4P2O7 + _____H2O

b) ___2__C6H6 + ___15__O2 ___12__CO2 + __6___H2O

c) ___2__Al(OH)3 + ___3__H2SO4 _____Al2(SO4)3 + ___6__H2O

14.What adjustments, if any, need to be made to your guidelines in order to balance the equations above?

Student answers may vary. However, the purpose of this question is to show students that there are a few helpful guidelines to use when balancing equations:

• Save H and O for last.

• Keep polyatomic ions together when possible (treat them as a unit).

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Can A Molecule Be Identified by its Percent Composition?

Background Information: Percent Composition

The percent composition (by mass) of an element in a molecule is the mass of the element in the molecule divided by the mass of the entire molecule times 100. Or, because the number of atoms (molecules) is proportional to the number of moles of atoms (molecules),

Percent composition of element x = mass of x in one mole of the compound x 100 Mass of one mole of the compound

% Ba in BaCl 2 = mass of Ba in 1 mole of BaCl 2 x 100

mass of 1 mole of BaCl 2

% Ba in BaCl2 = 137.3 grams Ba x 100 = 65.91% Ba in BaCl2

208.3 grams BaCl2

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Group Activity

1. Fill in the missing molecular formulas using the structural formulas in Table 1. 2. Find the % composition of benzene, cyclobutane, and 1-octene.

3. Verify that the % composition given for ethyne in Table in Table 1 is correct.

4. Is it possible, given the original data in Table 1, to determine the % composition by mass of H for 2-butene without using the equation given in the model above? If so, how?

5. Based on the data in Table 1, is it possible to determine the molecular formula of a compound solely from its percent composition? Why or why not?

6. What is similar about the molecular formulas of cyclobutane and 1-octene? 7. Compare the molecular formulas of ethyne and benzene?

8. What mathematical relationship do all compounds with the same % composition have?

Background Information: Empirical Formula

The empirical formula of a compound describes the relative number of each type of atom in the compound. It is given in terms of the smallest-possible-whole-number ratios (as subscripts). For example, the empirical formula of ethane is CH3. (Note that the subscript “1” is omitted.)

Group Activity

9. Write the empirical formulas for all of the compounds in Table 1.

Independent Activity

1. The molecule 2-hexene has the molecular formula C6H12. Refer to Table 1 and determine the

percent composition of H in the molecule.

2. Determine the percent composition of each element in acetic acid, CH3COOH.

3. A molecule containing only nitrogen and oxygen, contains 30.4% N by mass. (a) How many grams of N would be found in a 100.0 g sample of the compound? (b) How many grams of O would be found in the same sample of the compound? (c) How many moles of N would be found in a 100.0 g sample?

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) (e) What is the ratio of number of moles of O to number of moles of N?

(f) What is the empirical formula of the compound?

4. An unknown liquid contains 38.7% C and 51.6% O by mass. The remainder of the compound is H. What is the empirical formula?

5. Holt, Rinehart, Winston 2002 Text. Chapter 7,p. 229 - 231 practice problems 1-3, p. 231; p. 232-233, practice problems 1 and 2 and section review problems 1-5, p. 233; p. 237 problems 36-39, 47, 50, and 52.

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Limiting Reagent (Reactant)

Model 1: The S’more

A delicious treat known as a S’more is constructed with the following ingredients and amounts: 2 graham crackers 1 chocolate bar 2 marshmallows

At a particular store, these items can be obtained only in full boxes, each of which contains one gross (144) of items. A gross is a specific number of items, analogous (but not equal) to one dozen. The boxes of items have the following net weights ( the weight of the material inside the box):

Box of graham crackers 9.0 pounds Box of chocolate bars 36.0 pounds Box of marshmallows 3.0 pounds

Group Activity

1. Based on the information given, which of the three ingredients (a graham cracker, a chocolate bar, or a marshmallow) weighs the most? Which weighs the least?

2. If you have a collection of 100 graham crackers, how many chocolate bars and how many marshmallows do you need to make S’mores with all of the graham crackers?

3. If you have a collection of 1000 graham crackers, 1000 chocolate bars, and 1000 marshmallows, how many S’mores can you make? What will be left over?

4. If you have 36.0 pounds of graham crackers, 36.0 pounds of chocolate bars, and 36.0 pounds of marshmallows, which item do you have the most of? The least? Explain your reasoning 5. a) If you attempt to make S’mores from the material described in question #4, what item

will you run out of first? (This item is known to chemists as the limiting reagent

because it is the reactant which limits the amount of product which can be made.) b) How many gross of S’mores will you have made?

c) How many gross of each of the two left over items will you have? d) How many pounds of each of the left over items will you have? e) How many pounds of S’mores will you have?

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 6. Using G as the symbol for graham crackers and Ch as the symbol for the chocolate bars and

M for marshmallows, write a “balanced chemical equation” for the production of S’mores. 7. Why is it not correct to state that if we start with 36 pounds each of G, Ch, and M, then we

should end up with 3 x 36 = 108 pounds of S’mores?

Model 2: Water

8. 25.0 grams of hydrogen and 25.0 grams of oxygen react to form water. a) Write the balanced chemical equation and show all steps.

b) Assuming that the reaction goes to completion, which element will be totally consumed in the formation of water?

c) What is the limiting reagent?

d) How many grams water can be produced?

e) How many grams of the excess element remain unreacted?

Independent Activity #1

Read p. 288-292 Modern Chemistry Text

1. Given the balanced chemical equation: 2 NO(g) + O2(g) 2 NO2(g)

calculate the mass of nitrogen dioxide that can be made from 30 grams of NO and 30 grams of O2.

2. Zinc and iodine, I2, react to form zinc iodide, ZnI2 (the reactants and the product are all solids

at room temperature).

a) Write a balanced chemical equation for this reaction.

b) Suppose that 50.0 g of zinc and 50.0 g of iodine are used to form zinc iodide. 1) Assuming that the reaction goes to completion, which element will be totally

consumed in the formation of the zinc iodide? 2) What is the limiting reagent?

3) How many grams of zinc iodine can be produced?

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Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 3. Acetylene gas, HCCH, is commonly used in high temperature torches.

a) Write a balanced chemical equation for the reaction of acetylene with hydrogen gas (H2)

to form ethane (C2H6).

b) How many grams of ethane can be produced from a mixture of 30.3 grams of HCCH and 4.14 grams of H2?

4. Titanium (Ti) is a strong, lightweight metal that is used in the construction of rockets, jet engines, and bicycles. It can be prepared by reacting TiCl4 with Mg metal at very high

temperatures. The products are Ti(s) and MgCl2(s).

a) Provide a balanced chemical reaction for the reaction described above.

b) How many grams of Ti metal can be produced from a reaction involving 3.54 x 104 g of TiCl4 and 6.53 x 103 g of Mg?

Independent Activity #2

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Developed by Alabama Science in Motion teachers Summer, 2003.

Page 1 Revised 8/2/2005

LABORATORY SAFETY

(How can we all survive chemistry labs?)

Why: The chemistry laboratory is a potentially hazardous place to work. There are

dangerous substances and equipment that must be handled with care. This exercise is designed to construct student knowledge of common lab safety issues. and to focus on the importance of laboratory safety and the procedures to execute before, during, and after laboratory activities.

Group Members

Group Activity

1. Brainstorm as many lab safety rules as you can within your group (time limit 5 minutes).

2. Determine the top five safety rules from the list generated by your group and rank them in order of importance.

3. Your instructor will supply you with a random list of lab safety rules. Rank these safety rules in order of decreasing importance (most important to least important).

4. Place an asterisk beside the top five rules identified by your group in question 2 that appear on the instructor’s list.

5. Compare your group’s brainstormed list to the instructor’s list. Account for any differences that you find.

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Page 2 Revised 8/2/2005 6. Design an emergency procedure to use in the event of each of the situations listed below

in which the instructor is incapacitated (unconscious) and students have to react responsibly to the situation to reduce injury and panic.

• A chemical table or floor fire

• An individual’s clothing catches on fire

• A cut or a burn injury

• An eye injury

• An acid spill

• A base spill

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Page 3 Revised 8/2/2005 7. Identify these safety symbols and determine their proper location in your school lab.

Floor Plan: In the space below draw a sketch of the floor plan of your school’s chemistry laboratory. There should be 2 exits from your lab. (NOTE: Sometimes a window is considered an alternative exit.) Locate both exits on your floor plan and label where the safety goggles, safety shower, eye wash station, and fire extinguisher are located.

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Review Activity

Each group will choose one of the safety procedures and create a laboratory safety poster for display in the classroom.

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Instructor’s Safety List

Acids should be transferred to water only (never add water to acid). Aprons must be worn at all times.

Bunsen burners should be monitored at all times.

Chemicals must be transferred from large stock bottles to small manageable containers. Fire blankets should be used on individuals in case of fire.

Fire extinguishers should not be used on individuals.

Broken glassware should be disposed of in its proper container. Goggles must be worn at all times.

Long hair should be tied back. Loose clothing should not be worn. No eating or drinking in the laboratory. No horseplay in the laboratory.

Open-toed shoes should not be worn.

Solid substances should not be disposed of in the sink unless approved by your instructor. Unlabeled glassware with unknown substances should not be used.

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Page 1

The Mole Concept

Why: Samples of matter are composed of numerous particles (atoms, ions, or molecules). Because the numbers of particles are so huge, chemists have established a unit of

measure called the mole (abbreviated mol) for use in counting them. In this activity you will discover the relationship between the term “mole” as it relates to the number of particles and the mass of the particles.

Model 1:

Below are some equivalent quantities with which you may or may not be familiar: 1 pair of shoes = 2 shoes

1 dozen donuts = 12 donuts

1 ream of copy paper = 500 sheets of copy paper 1 gross of pencils = 144 pencils

One elephant has one trunk and four legs.

Equivalent quantities may be used as conversion factors. A conversion factor is written as a fraction where the numerator and denominator are expressed in different units but are equal quantities. For example:

1 ream of copy paper OR 500 sheets of copy paper 500 sheets of copy paper 1 ream of copy paper Because the numerator and denominator represent the same thing, only in different units, conversion factors are always = 1.

Equivalent quantities (conversion factors) used in the study of chemistry: 1 mole of items = 6.022 x 10 23 items (Avogadro’s Number)

(items = atoms, molecules, ions or formula units)

One methane molecule, CH4, contains one carbon atom and four hydrogen atoms.

Key Questions:

If your answer is extremely large or small, use scientific notation form. Include units for all answers. Show your work.

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Page 2 2. How many legs are found in one dozen elephants?

3. How many trunks are found in a ream of elephants?

4. How many legs are found in a pair of elephants?

5. How many carbon atoms are found in one dozen methane (CH4) molecules?

6. How many hydrogen atoms are found in one dozen methane molecules?

7. How many carbon atoms are found in a pair of methane molecules?

8. How many hydrogen atoms are found in a ream of methane molecules?

9. How many elephants are there in one mole of elephants?

10. How many trunks are found in one-half mole of elephants?

11. How many legs are found in one mole of elephants?

12. How many methane molecules are there in one mole of methane?

13. How many carbon atoms are found in one mole of methane molecules?

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Page 3

Model 2:

The mass of 1 mole of any pure substance = average atomic mass expressed in grams of that substance. For example:

1.008 amu = average atomic mass for H 1.008 g H = 1 mol H

15. Where would you find the average atomic mass for carbon?

16. What is the average mass (in amu) of one carbon atom?

17. What is the mass (in grams) of one mole of carbon atoms?

18. What is the average mass (in amu) of one methane molecule?

19. What is the mass (in grams) of one mole of methane molecules?

20. How is the mass in amu of one atom of an element related to the mass in grams of one mole of that element?

21. Refer to questions #12 and 19. If you measured out the mass of methane in your response to question 19, how many methane molecules would you have?

22. If you measure out 58.69 g of Ni, how many nickel atoms would you have?

23. If you want to measure out 3.011 x 1023 atoms of gold, how many grams would you need to measure out?

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Page 4 Complete the Table below by supplying the necessary information.

Substance Number of Particles Mass in grams Al 6.022 x 1023 atoms

H2O 18.02 g

O2 1.505 x 1023 molecules

Ne 10.09g

Skill Development Exercises:

1. Indicate whether each of the following statements is true or false and explain your reasoning.

A. One mole of NH3 weighs more than one mole of H2O.

B. There are more carbon atoms in 48 grams of CO2 than in 12 grams of diamond (a

form of pure carbon).

C. There are equal numbers of nitrogen atoms in one mole of NH3 and one mole of N2.

D. The number of Cu atoms in 100 grams of Cu(s) is the same as the number of Cu atoms in 100 grams of copper (II) oxide, CuO.

E. The number of Ni atoms in 100 moles of Ni(s) is the same as the number of Ni atoms in 100 moles of nickel (II) chloride, NiCl2.

F. There are more hydrogen atoms in 2 moles of NH3 than in 2 moles of CH4.

2. Use grammatically correct sentences to describe how to calculate the number of H atoms in any number of moles of NH3.

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Page 5

The Mole Concept

Teacher Notes

Time Required: One 50 minute class period.

Prerequisites:

Knowledge of average atomic mass, the use of the Periodic Table to find an element’s average atomic mass, and the calculation of a formula mass

1. Understand the relationship between the unit “mole” and Avogadro’s number. 2. Define the gram formula mass of a substance.

3. Understand the relationship between the mole and the gram formula mass.

Performance Criteria:

1. Perform conversions between mass, moles, and numbers of particles.

Considerations:

This activity is a wonderful way to introduce the concept of moles to an introductory chemistry class. No previous knowledge of moles is required.

Closure:

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Page 6

Answers to Questions: Model 1 – Key Questions:

1. 12 trunks 2. 48 legs 3. 500 trunks 4. 8 legs

5. 12 carbon atoms 6. 48 hydrogen atoms 7. 2 carbon atoms 8. 2000 hydrogen atoms 9. 6.022 x 1023 elephants 10.3.011 x 1023 trunks 11.2.409 x 1024 legs 12.6.022 x 1023 molecules 13.6.022 x 1023 carbon atoms 14.1.204 x 1024 hydrogen atoms

Model 2

15.periodic table 16.12.01 amu 17.12.01 g 18.16.05 amu 19.16.05 g

20.One atomic mass unit (amu) equals the mass in grams of one mole of an element. 21.6.022 x 1023 molecules

22.6.022 x 1023 atoms 23.98.99 g

Substance Number of Particles Mass in grams Al 6.022 x 1023 atoms 26.98 g

H2O 6.022 x 1023 molecules 18.02 g

O2 1.505 x 1023 molecules 8.00 g

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Page 7

Skill Development Exercises:

1.

a. False, NH3 1 mole = 17.03 g, H2O 1 mole = 18.02 g

b. True, there are 6.57 x 1023 atoms of carbon in 48 g of CO2 and only 6.016 x 1023 atoms of

carbon in 12 g of diamond

c. False, 1 mole of NH3 = 6.022 x 1023 atoms of nitrogen, 1 mole of N2 = 1.2044 x 1024 atoms of

nitrogen

d. False, 100 g of Cu = 7.57 x 1023 atoms of copper, 100 g of CuO = 9.48 x 1023 atoms of copper

e. True, Since 1 molecule of NiCl2 contains 1 atom of nickel then 1 mole of NiCl2 would

contain 6.022 x 1023 atoms of nickel. One mole of nickel also contains 6.022 1023 atoms of nickel.

f. False, In 2 moles of NH3 there are 3.61 x 1024 hydrogen atoms but in 2 moles of CH4 there are

4.82 x 1024 hydrogen atoms.

2.

In one molecule of NH3 there are three atoms of hydrogen and in mole of NH3 there are

6.022 x1023 molecules of NH3. To determine the number of hydrogen atoms in any number of

moles, multiply the number of moles by 6.022 x 1023 to convert to molecules. Then convert molecules to atoms by multiplying by three.

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1

What is an Atom?

Background Information:

An atom is defined as the smallest particle of an element that retains the chemical properties of that element. All atoms are composed of the same basic particles, but all atoms are not the same. The Periodic Table is a useful tool for determining the number of particles in different atoms. Here is the Periodic Table entry for the element carbon:

Atomic number

Atomic symbol

Atomic mass

Model: Schematic Diagrams for Various Atoms and Ions

6

C

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2

Group Members

:

Group Activity:

1. How many protons are found in 12C? 13C? 13C-?

2. How many neutrons are found in 12C? 13C? 13C-?

3. How many electrons are found in 12C? 13C? 13C-?

4. Based on the background information,

a) what do all carbon atoms (and ions) have in common?

b) what do all hydrogen atoms (and ions) have in common?

5. Look at the Periodic Table provided. The atomic number (normally referred to as Z) is the number given above each element’s symbol. What is the significance of this atomic number?

6. What do all nickel (Ni) atoms have in common? (refer to the periodic table if needed)

7. How is the mass number (normally referred to as A) of an atom (or ion) determined? (NOTE: The mass number is the superscript number to the left of the atomic symbol.)

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3

Model: Schematic Diagram of Various Atomic Changes

Loss of electrons Gain of electrons

Change in atomic mass (or neutrons)

Positive Negative

Ion Ion

Isotope

9. a) What distinguishes a neutral atom from an ion?

b) How is the charge on an ion determined?

10.Where is most of the mass of a neutral atom, ion and isotope found? Within the nucleus or outside of the nucleus? Explain your reasoning.

11.What is the mass (in grams) of one 1H atom? Of one 12C atom?

Review Questions/Problems (Individual Effort):

1. Read pages 75-82 in your textbook.

2. Study Sample Problem 3.1 on page 77. Review Practice Problems on page 78.

Neutral Atom

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4

Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) 3. Complete the following table:

ISOTOPE ATOMIC NUMBER ATOMIC MASS NUMBER OF ELECTRONS 31

P 15

18

O 8

19 39 18

58

Ni2+ 58

27 59 25

14

N

3 7 3 3 6 3

58

Zn2+

19

F-

4. How many electrons, protons and neutrons are found in each of the following? a) 24Mg

b) 23Na+

c) 35Cl

d) 35Cl

-e) 56Fe3+

f) 15N

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5

Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.) h) 27Al3+

5. What is the mass (in grams) of 4.35 x 106 atoms of 12C?

6. a) Define atomic mass (A). b) Define atomic number (Z).

Sources:

1. Davis, Raymond E., et al, Modern Chemistry, Holt, Rinehart and Winston, 2002, pages 75-82.

2. Farrell, John J. and Moog, Richard S., Chemistry: A Guided Inquiry, John Wiley & Sons, 1999, pages 1-4.

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6

What is an Atom?

Teacher Notes

Time Required: One 50 minute class period.

Prerequisites:

Knowledge of basic dimensional analysis, calculation of unit conversions

1. Identify the basic subatomic particles.

2. Understand the relationship between subatomic particles, atomic number, and atomic mass.

3. Identify the nucleus of an atom and the subatomic particles contained in it.

Performance Criteria:

1. Recognize the relationship between the atomic number of an element and its placement on the Periodic Table.

Considerations:

This activity is a wonderful way to introduce the concept of basic atomic structure. No previous knowledge of atoms is required.

Closure:

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7

Answers to Questions in Group Activity:

1. 6, 6, 6 2. 6, 7, 7 3. 6, 6, 7

4. a) all have 6 protons b) all have 1 proton 5. It is the same as the number of protons. 6. They must all have 28 protons.

7. It is the total of the protons and neutrons.

8. The number of neutrons is different (which makes the mass different).

9. a) an ion is charged b) adding the protons (pluses) and electrons (minuses) together equals the charge

10.inside the nucleus because that is where the protons and neutrons are located. The atomic masses don’t agree if you add in the electrons that are outside of the nucleus.

11.1.0078 amu x 1.6606 x 10-24 g = 1.6736 x 10-24 g for the 1H atom 1 amu

12 amu x 1.6606 x 10-24 g = 1.9927 x 10-23 g for the 12C atom 1 amu