DidYouKnow?, When you buy a carton that says it contains one …€¦ · DidYouKnow?, The Mole For convenience, chemists group particles by large numbers that are easier to work with

When you buy a carton that says it contains one dozen eggs, you know thatthe carton contains 12 eggs. The teffil "dozen" is a counting unit. You usecounting units for convenience all the time. For example, you group yoursocks into counting units of two, called pairs. You might buy a six-pack ofsoft drinks.

DidYouKnow?,

The MoleFor convenience, chemists group particles by large numbers that are easier towork with. The numbers of elementary entities (atoms, molecules, or formulaunits) in even a small sample of a substance are enormous. Therefore, theyare grouped by an extremely large number. The grouping that chemistsuse is called the mole.

Notice that there are nine significant digits in the most precise and accuratedetermination of Avogadro's number to date. You will rarely need this levelof precision. In this textbook, you will use the value 6.02 X 1023. For example,there are 6.02 X 1023 carbon atoms in 1 mol of carbon, C. There are6.02 X 1023 carbon dioxide molecules in 1 mol of carbon dioxide, CO2.There are 6.02 X 1023 sodium chloride formula units in 1 mol of sodium

chloride, NaCI(s)'

The Magnitude of Avogadro's NumberThe number 6.02 X 1023 is enonnous. One way toappreciate the vast size of the number is to relateit to everyday objects that you can visualize.Figures 3.22 and 3.23 provide some examples.In Think and Link Investigation 3-E, youwill visualize covering the surface of Albertawith 6.02 X 1023 pennies.

.t:::J:>

.:aI:!::!;t;:.~

It cost about $3.5million to build the Calgary Tower.Suppose you could build threeCalgary Towers each second,spending $3.5 million to buildeach tower. If you began with$6.02 x 1023, it would takenearly 2 billion years to go broke.

Measure the height of a pile of fiveloonies. How tall, in kilometres, would be a stackof 6.02 x 1023 loonies?

116 MHR . Unit 1 Energy and Matter in Chemical Change

Avogadro's number is named tohonour the Italian chemist AmedeoAvogadro (1776-1856). In 1811,Avogadro postulated what is nowknown as Avogadro's law. Thelaw states that equal volumesof gases, at equal temperaturesand pressures, contain the samenumber of molecules. This lawwas eventually used to determinemolar masses. Unfortunately,the importance of Avogadro'slaw was not recognized untilseveral years after his death.He never knew the numberthat now bears his name.

Think About It LIn this investigation, you will consider the following scenario. You have 6.02 X 1023pennies, which you are going to use to cover the surface of Alberta. What will bethe height of the layer of pennies? You will stack the pennies in columns of roughlyequal height. The columns must touch at the bottom.

What to Do0 As a group, design a procedure for answering

the question above. You will need to considerseveral variables, including the following:. How will you determine the surface area

of Alberta?. How will you layout the pennies?

. How will you determine the height of

a penny?. Carry out your procedure to determine theheight of the layer of 6.02 X 1023 pennies.

. Write a detailed report showing what you didand how you arrived at your answer. Pay carefulattention to significant digits in your measure-ments and calculations. Include answers to theAnalyze questions below in your report.

Chapter 3 Chemical Reactions. MHR 117

Relating Mass and AmountOn its own, thinking of atoms and molecules in amounts of 6.02 X 1023 particlesis of little practical use. There needs to be a convenient way to measure amountsof substances in moles. Fortunately, it is possible to calculate what mass ofa substance is equal to one mole of that substance. To do this, chemists usethe relative masses of elements.

www.mcgrawhill.ca/links/sciencefocus10

The mole has its own day! Mole Day begins at 6:02 A.M. and endsat 6:02 P.M. on October 23 each year. Why are those times and that date appropriate?

High school teachers and students throughout the world take part by writing jokes, songs,and poems, and by participating in projects to celebrate the mole and chemistry in general.

What is the theme of this year's Mole Day and how can you participate? Go tothe web site above to find out where to go next. Prepare a brief

proposal outlining three possible ways your classcould get involved in Mole Day.

Find OutCan You Count on It?Chemists and chemical engineers usually need

to control the number of atoms, molecules, and

ions in their reactions very carefully. Chemists

can calculate the approximate numbers of the

particles by measuring their masses. How

accurate is this method?

5. Develop and carry out a method to determinethe number of items in the bag withoutopening it.

What Did You Find Out? . r:1"i"'!)~" ,I~~ r, "~l i! liii:':;i~j,:;ii!..~

1. According to your determination, how manyitems are in the bag?

2. Explain how you determined that number.Materials

small identical items to be counted(e.g., paper clips or bingo chips)

re-sealable plastic bag

electronic balance

3. After calculating the number of items in thebag, open the bag and count the numberof items. Compare your calculated numberof items with the actual number of items.

Procedure - ~~~ i[i[lJ.i[j1]llJ~" rci:l 11:;:~JJ iLrll~~

4. Discuss the accuracy of your method ofdetermining the number of items in theplastic bag. What are some sources oferror that may have affected your results?

2. Determine and record the mass of an emptyre-sealable plastic bag. 5. In this activity, you were able to count

manually a group of small items and measure

the total mass of the group to determine an

average mass. Do you think chemists are able

to determine the average mass of an atom

or molecule in the same way? Explain

your answer.

3. Fill the bag to the brim with items and seal it.

4. Determine and record the mass of the filled

plastic bag.

118 MHR. lrld Matter in Chemical Chang-e

1. Count out a small number of items andmeasure their mass. Record the numberof items and the mass.

The Atomic Molar Mass of an ElementThe atomic molar mass (M) of an element is a weighted average of themass of 1 mol of all of the naturally occurring isotopes of the element. Youcan find the atomic molar mass listed for each element on the periodic table.For example, the atomic molar mass of iron is listed on the periodic table as55.85 g/mol. In other words, the mass of 1 mol of iron is 55.85 g. Similarly,the atomic molar mass of sodium is 22.99 g/mol. Therefore, the mass of 1 molof sodium is 22.99 g. Figure 3.24 shows samples of elements. Each samplecontains 6.02 X 1023 atoms, or 1 mol.

Each sample above contains 6.02 x 1023 atoms. Note that the mass ofeach sample is different.

Some elements exist as molecules, not atoms. For example, the elementnitrogen exists as a molecule composed of two nitrogen atoms, N2(g). Therefore,1 mol of nitrogen molecules contains 2 mol of nitrogen atoms. The molar massof nitrogen molecules is therefore twice the atomic molar mass of nitrogen asshown on the periodic table: 2 X 14.01 g/mol = 28.02 g/mol. In other words,1 mol of molecular nitrogen has a mass of 28.02 g.

The Molar Mass of a CompoundThe tenn molar mass (M), with units of g/mol, is used to refer to the mass of1 mol of any pure substance. You can detennine the molar mass of a compoundby using the fonnula of the compound. For example, the fonnula of carbondioxide, CO2 (g), tells you that each molecule contains one carbon atom andtwo oxygen atoms.


By extension, 1000 molecules of CO2(g) contain 1000 carbon atoms and 2 X 1000oxygen atoms. Further, 6.02 X 1023 molecules of CO2 contain 6.02 X 1023carbon atoms and 2 X 6.02 X 1023 oxygen atoms. In other words, 1 mol ofCO2(g) contains 1 mol of carbon atoms and 2 mol of oxygen atoms. Therefore,the molar mass of a molecular compound may be calculated as follows:

mass of 1 mol of CO2(g)= (1 mol C X Mc) + (2 mol 0 X Mo)= (1 IJ!~ X 12.01 g/IJ!~ + (2 IJ!!)l.er X 16.00 g/IJ!~= 44.01 g

Therefore, the molar mass of carbon dioxide is 44.01 g/mol.You can calculate the molar mass of an ionic compound in the same way:

mass of 1 mol of Mg(NO3)2(s)= (1 mol Mg X MMg) + (2 mol N X MN) + (6 mol 0 X Mo)= (1 ~l.Mg"X 24.31 g/~.Mg) + (2 ry-M"X 14.01 g/ry-N> +

(6 ~-6' X 16.00 g/~-6)= 148.33 g

Therefore, the molar mass of magnesium nitrate is 148.33 g/mol.Figure 3.25 shows some examples of molar amounts of substances and their

masses. Try the following problems to practise detennining molar masses.

Each sample showncontains 6.02 x 1023 moleculesor formula units.


Converting Between Mass and MolesIt is often useful for chemists to convert between the amount of a sampleexpressed in moles and the mass of the sample expressed in grams. To do this,you can use a method called the factor label method. The factor label methoduses conversion factors to change units without affecting the value. You can useconversion factors to change an amount of a sample expressed in moles to themass of the sample, expressed in grams. In this case, the conversion factor isthe molar mass of the substance. For example, to determine the mass of2 molof helium, use the molar mass of helium, 4.00 g/mol, as a conversion factor.You can do this because 4.00 g of helium is equivalent to 1 mol of helium.

. £ 4.00 g HeconverSIon actor =1H1 mo e

Multiply 2 mol by the conversion factor to determine its mass.

f h 1. 2 ,...~ 4.00 g Hemass 0 ernm= ~ eX ,...~

l~ e

= 8.00 gHe

Notice that the answer has the desired units, grams. Model Problem 1 showshow to use this method to convert from amount to mass of a compound. Youcan use the inverse of the molar mass to convert from mass to amount, asshown in Model Problem 2.

Alternatively, you may use the following equation to convert between massand moles:

m n = amount (mol)m = mass (g)M = molar mass (g/mol)

n=-M


Acro~;ICanadaMost people are familiar with stories of OlympicTM athletes who enjoythe triumph after being declared the winner in their sport. Thetriumph is short-lived for a few athletes, however, if the gold medalis denied them because they have tested positive for performance-enhancing drugs. Who conducts the tests for these substances,and how are these tests conducted?

Dr. Christiane Ayotte has been the head of Canada's DopingControl Laboratory since 1991. When a urine sample arrives at thedoping control lab, Dr. Ayotte and her team ensure careful handlingof the sample. Portions of it are taken for six different analyticalprocedures. The more than 150 substances banned by the inter-national Olympic Committee (IOC) are grouped according to theirphysical and chemical properties. There are two main steps inanalyzing a sample:

1. purification, which involves steps such as filtration and extractionusing solvents, and

2. analysis by gas chromatography, mass spectrometry, or high-performance liquid chromatography. Chromatography is a partof the processes whereby chemists separate mixtures intopure substances.

Just the presence of most banned substances in a urine samplemeans a positive result. Other substances must be present in anamount higher than a certain threshold. This is when knowing aboutchemical amounts comes in handy. A male athlete would have to


consume 10 very strong cups of coffee within 15 min to go over thelimit for caffeine. Ephedrines and pseudoephedrines, two decon-gestants that are found in cough remedies and act as stimulants,have a cut-off level that allows athletes to take them up to one ortwo days before a competition.

Dr. Ayotte and her team are constantly searching for reliabletests for natural substances, developing new analytical techniques,and determining the normal levels of banned substances for maleand female athletes. These arejust part of the challenges sheand her team face. Dr. Ayottemust also defend her testsin hearings and with thepress, especially whenhigh-profile athletes areinvolved. Dr. Ayotte's findingsare sometimes unpleasant toreport. However, she believesthat integrity and a logicalmind are essential aspectsof being a good scientist.

Dr. Christiane Ayotte -

Working with the MoleThe best way to get better at working with the mole is to practise. Sharpenyour skills by working through the following Practice Problems.

15. Determine the molar mass of the following elements.

(a) cesium, CS(t')

(b) gold, Au(s)

(c) hydrogen, H2(g)

(d) nitrogen, N2(g)

16. Determine the molar mass of each of the following compounds.

(a) NO3(g) (c) FeSO4(s)

(b) Al2S3(s) (d) <NH4)2CO3(s)

17. mat is the mass, in grams, of 8.52 mol of each of thefollowing substances?

(a) H20(t') (c) NiCI2(s)

(b) Al(s) (d) 02(g)

18. What is the amount, in moles, of 342.5 g of each of thefollowing substances?

(a) W(s) (c) SS(s)

(b) NCI3(f) (d) Ca(NO3)2(s)

19. Express the following as molar amounts.

(a) 10.00 g CO2(g) (c) 14.00 g Cr(OH)3(s)

(b) 3.50 g CSH12(g) (d) 6.97 g Al(NO3)3(s)

20. Re-order each of the following groups of substances from lowestto highest molar mass.

(a) Nb(s), Ti(s), U(s), Sb(s)

(b) F2(g), 12(s), CI2(g), Br2(f)

(c) lr(s), Se(s), GaP(s), HCIO3(s)

(d) NH3(g), SO2(g), K3PO4(s), Pb(s)

21. A student writes down the following information.mass of beaker = 52.43 gmass of beaker and CuSO4(s) = 65.41 g

What amount of CUSO4(s), in moles, did the student add tothe beaker? '

22. A student uses a graduated cylinder to measure 25.5 mL of waterat 25°C. The density of water is 1.00 g/mL at 25°C.

(a) What is the mass of the water in the graduated cylinder?

(b) What amount of water, in moles, is in the graduated cylinder?

Chanter 3 Chemical Reactions. MHR 123

The Mole and the Law of Conservation of MassUsing the mole concept, you can relate the coefficients in balanced chemicalequations to the mass of the substances involved. Start by thinking abouthow the coefficients relate tq moles of substances. For example, considerthis chemical equation:

2HZ(g) + Oz(g) --7 2HzO(t')

You can multiply all of the coefficients by two and the equation will remainbalanced. Four molecules of hydrogen react with two molecules of oxygen toform four molecules of water. There are then eight hydrogen atoms on thereactant side and on the product side. There are four oxygen atoms on thereactant side and on the product side. In fact, as shown below, you can multiplythe coefficients by any factor you like.

2H2(g) + 02(g) ~ 2H20(i)

2 molecules 1 molecule 2 molecules2 x 2 molecules 1 x 2 molecules 2 x 2 molecules2 x 1000 molecules 1 x 1000 molecules 2 x 1000 molecules2 x 6.02x1023 molecules 1 x 6.02x1023 molecules 2 x 6.02x1023 molecules2 mol 1 mol 2 mol

Pause&'_0- - Reflect 1

Examine Table 3.5. Use calculationsto demonstrate that 2 mol H2,1 mol 02, and 2 mol H2O eachhave the mass shown on thetable. Then write a balancedchemical equation for theformation of sodium chloride,NaGI. Make a table similar toTable 3.5 to show that theequation is consistent with thelaw of conservation of mass.

Notice that 2 X 6.02 X 1023 molecules is the same as 2 mol of molecules.In the same way, 1 X 6.02 X 1023 molecules is the same as 1 mol of molecules.Now you have two ways to interpret the coefficients of a balanced chemicalequation. The coefficients can represent the number of particles (molecules orformula units) involved in the reaction. Or, the same coefficients can representthe amount in moles of each substance involved in the reaction.

In Table 3.5, you can see how molecules, moles, and mass are related in thechemical equation. Notice that the total mass of the product is equal to thetotal mass of the reactants. If you carry out this comparison with any balancedchemical equation, you will see the same thing. The total mass of the substanceson the products side equals the total mass of the substances on the reactantsside. You know from Section 3.3 that balanced chemical equations obey thelaw of conservation of mass when the coefficients refer to atoms, molecules,or formula units. Table 3.5 shows that balanced chemical equations also obeythe law of conservation of mass when they refer to moles.

Table 3.5 Chemical Equations and The Law of Conservation of Mass


Section 3.4 SummaryIn this section, you learned how the mole connects the amount of a substanceto its mass. The concept of the mole plays a major role in predicting howmuch of a given substance is consumed or produced in a chemical reaction.In later science or chemistry studies, you will learn more about the mole andits role in predicting quantities involved in chemical reactions.

Check Your Understanding

1. Write a paragraph to describe the mole and Avogadro's number, andexplain their importance in chemistry.

2. One mole of atoms of any element contains 6.02 X 1023 atoms. Explainwhy elements have different molar masses.

3. Find the molar mass of each of the following pure substances.

(a) ozone, 03(g)(b) carbon monoxide, CO(g)

(c) methane, C~(g)(d) calcium carbonate, CaC03(s)

(e) ammonium nitrate, NH~03(s)

(1) aluminium sulfate, All (504)3(s)

4. How many molecules are there in 1 mol of water?

5. Detennine the mass of each of the following samples.

(a) 3.52 mol silicon, Si(s)

(b) 0.0035 mol barium, Ba(s)

(c) 545.13 mol ammonium hydroxide, NH40H(s)

(d) 8.45 X 10-4 mol zinc phosphate, Zn3(PO4)2(s)

6. Express the following as molar amounts.

(a) 2.33 g hydrogen chloride, HCI(g)

(b) 16.0 kg carbon dioxide, CO2(g)

(c) 1.03 X 105 g propane, C3Hs(g)

(d) 6.84 g sucrose, C12H22011(s)

7. Thinking Critically Chemical equations are sometimes written withfractions as coefficients. For example:

5C2H2(g) + 2" 02(g) ~ 2CO2(g) + H20(g)

(a) Demonstrate that the equation is balanced.

(b) Does using fractions as coefficients make sense if you consider thatthe coefficients refer to the numbers of molecules involved in thereaction? Explain your answer.

(c) Does using fractions make sense if you assume that the coefficientsrefer to moles of reactants and products? Explain your answer.


8. At the beginning of this unit, you learned that dyes can be obtained fromnatural sources such as plants. Dyes can also be produced synthetically. In1856, chemistry student William Perkin accidentally discovered a way toproduce a mauve dye synthetically. A dress that was dyed with the originalmauve dye is shown in Figure 3.26.

(a) The mauve dye, known today as mauveine or aniline purple, containsvarious compounds. One of the compounds is (C26H23N4)2S04(s).What is the molar mass of this compound?

(b) If you assume that mauveine consists exclusively of(C26H23N4)2S04(s), what is the mass of 5.8 X 103 mol?

(c) How many moles of mauveine are contained in 25 tonnes?

~ Perkin's mauve dye started a fashioncraze. Because he made his discovery while hewas trying to produce something entirely different,Perkin's invention is an example of the role of luck inscientific discovery. Luck, however, was not enough.Perkin needed to analyze what at first seemed to bea failed experiment.

126 MHR . Unit 1 Energy and Matter in Cheinical Change

Now that you have completed this chapter, try to do the following. If youcannot, go back to the sections indicated in parentheses after each part.

(a) Describe evidence that would suggest thata chemical change has taken place. (3.1)

(h) Write the balanced chemical equations for specificexamples of a fonnation reaction, a decompositionreaction, a single-replacement reaction, anda double-replacement reaction. (3.3)(b) Describe how to distinguish between an exother-

mic reaction and an endothermic reaction. (3.1)

(i) Define the term "hydrocarbon." Give examplesof at least two different hydrocarbons and theiruses. (3.3)

(c) State the law of conservation of energy. Describehow the law applies to both exothennic andendothermic chemical reactions. (3.1)

(j) List the products of burning a hydrocarbonby complete combustion and by incompletecombustion. (3.3)

(d) Predict combinations of ions that will form aninsoluble compound in water, using a solubilitychart. (3.1)

(k) Explain the significance of Avogadro's number.

(3.4)(e) State the law of conservation of mass. How does

the law apply to chemical reactions? (3.2)

(1) Explain how to calculate the molar mass ofa compound, using an example. (3.4)(f) Explain why a balanced chemical equation is con-

sistent with the law of conservation of mass. (3.2)

(m) Show how to determine the number of molesin a given mass of a substance. (3.4)(g) Identify where you would place the tenn "thennal

energy" in an equation for a reaction that isexothennic and for one that is endothennic. (3.3)

I


Key Terms

coefficientformation reactiondecomposition reactionsingle-replacement reactiondouble-replacement reactionneutralization

organic chemistry

chemical reaction

chemical change

reactant

product

precipitateexothermic reaction

endothermic reaction

law of conservationof energy

law of conservation of massclosed system

open systemskeleton equationbalanced chemical equation

hydrocarboncomplete combustionincomplete combustionmole (mol)Avogadro's numberatomic molar mass (M)molar mass (M)factor label method

Understanding Key ConceptsSection numbers are provided if you need to review.

1. List five categories of evidence of chemicalreactions, and give examples of each. (3.1)

2. Distinguish between an exothermic change andan endothermic change. Give one example ofeach. (3.1)

3. Explain the importance of a closed system indemonstrating the law of conservation of massthrough experiment. (3.2)

Developing Skills9. Predict whether each of the following ionic

substances will be soluble in water.

(a) NaOH(s)

(b) CuCI(s)

(c) AgCIO3(s)

(d) ~CH3COO(s)(e) Pb(OH)2(s)

(f) SrSO4(s)

10. Write the balanced chemical equation for thedisplacement of aluminium in aluminium chlo-ride by magnesium.

4. Explain why a balanced chemical equation isconsistent with the law of conservation ofmass. (3.2) 11. Gold is usually found as small, uncombined pieces

of metal. One way to extract gold is to dissolveit in a cyanide solution (a hazardous procedure!).The gold can be precipitated from the cyanidesolution by adding a metal such as zinc:

2Au(CN)2(aq) + Zn(s) ~ 2Au(s) + Zn(CN)4(aq)

What type of reaction is this?

5. In what circumstances can incomplete combustionoccur, and why can it be dangerous? (3.3)

6. Qistinguish between a fonnation reaction anda decomposition reaction. Give one exampleof each. (3.3)

7. Which of the following compounds are hydro-carbons? Briefly explain your answers. (3.3)

(a) C3Hs(g)

(b) C6HuO6(s)

(c) H2CO3(s)

(d) CH30H(f)

(e) C6H6(f)

12. Write a balanced chemical equation for each ofthe following word equations. Use the descriptionof energy changes to write the term "thennalenergy" on the correct side of the equation.

(a) Solid sulfur combines with oxygen gasto form sulfur dioxide gas. The reactionis exothermic.

(b) Solid sulfur combines with oxygen gasexothermically to form sulfur trioxide gas.8. Describe the relationship between the mole and

Avogadro's number. (3.4)


17. As part of a laboratory procedure, a smdent mustdissolve 0.10 mol of silver nitrate, AgNO3(s),in 100 mL of distilled water. What mass ofsilver nitrate should the smdent add to thedistilled water?

(c) The decomposition of sulfur trioxide gasproduces sulfur dioxide gas and oxygengas. The process requires energy.

(d) The decomposition of carbon dioxidegas into solid carbon and oxygen gasis endothermic.

18. A student finds the mass of a small beaker to be12.5 g. The student adds some sodium hydrogencarbonate, NaHCO3(s), to the beaker and findsthe mass of the NaHCO3(s) and the beaker to be18.1 g. What amount of NaHCO3(s), in moles,did the student add to the beaker?

19. You begin with 15.0 g of sodium chloride. Youuse electrical energy to cause the sodium chlorideto decompose into its constituent elements.

(a) How many moles of sodium chloride didyou begin with?

(b) What do you predict will be the combinedmass of the products? Explain your answer.

13. Balance each of the following skeleton equations,write the word equation, and classify the reaction.

(a) Sn(s) + AgNO3(aq) ~ Sn(NO3)1(aq) + Ag(s)

(b) Al(s) + Ol(g) ~ AllO3(s)

(c) NaI(aq) + Pb(NO3)1(aq) ~

NaNO3(aq) + PbIl(s)

(d) CaCO3(s) + HCI(aq) ~ CaCI1(aq) + H1CO3(aq)

(e) MgIl(aq) + Brl(g) ~ MgBrl(aq) + Iz(s)

(f) <NH4)lS(aq) + Pb(NO3)1(aq) ~

PbS(s) + ~O3(aq)

14. Calculate the molar mass of each of the

following compounds:

(a) MnO2(s)

(b) Ba(OH)2(s)

(c) CSHlS(t')

(d) <NH4)2S04(s)

Critical Thinking20. Suppose that a winter stonn brings down electrical

lines over a wide area. You are told that there willbe no electricity for three or four days. It is bitterlycold outside and, unfortunately, your furnacecannot operate without electricity. Someonesuggests placing towels around doors and windowsto keep out drafts, and bringing in the barbecueas a source of heat. Why would this last actionbe very dangerous?

1 ~. Gasoline is a homogeneous mixture of hydrocar-bons. What is another name for a homogeneousmixture? A key compound in gasoline is octane,CaRls. Can you see from the formula why it hasthis name? Try to balance the equation for thecomplete combustion of octane.

Pause&ReflectProblem Solving! Applying

16. You have one solution that contains dissolvedsodium chloride, NaCI(aq), and another solutionthat contains copper(I) nitrate, CuNO3(aq). Youmix these solutions together. Do you expecta precipitate to form? Explain your answer.

Return to your notes and review your answers to the FocussingQuestions on page 82. Now that you have finished the chapter,how would you change your answers? Rewrite the responsesreflecting your change in thinking.


rtOver the past 50 years, countless industrial activitieshave taken place allover Earth. Unfortunately some ofthese activities have resulted in the contamination of soil.Researchers like Professor Selma Guigard and her studentsat the University of Alberta are working to perfect a processthat will remove unwanted or even dangerous metals fromsoil. Thanks to their work, contaminated soil can be madesafe and usable once more.

Q Is the method you are researching able to eliminatethose problems?

A Yes. We are using a different solvent to cleanthe soil - carbon dioxide, CO2. It is more

environmentally friendly than organic solvents,so there is no problem with disposal or unsaferesidues. We're not using CO2 in its naturalstate, though. We're using it in its supercriticalfluid form. Supercritical CO2 is the same thingsome manufacturers use to remove caffeinefrom coffee beans.

0 I've read about environmental companies using micro-organisms to clean soil. Does your research involveanything like that?

A No. Although it's popular for some clean-up

jobs, bioremediation is not terribly successfulin removing metals. Often the metals are toxicto the organisms that are meant to clean themup. The process we are investigating is a solventextraction technology. It is a process that hasbeen tried by others in the past, but the resultwas not very satisfactory.

Q Why not?

A The solvent that was used in the process wasusually an organic compound, such as methanol.It successfully cleaned the soil, but it left behinda residue that often made the soil useless foranything but landfill. As well, after the cleaning

, process, the contaminated solvent had to bedisposed of safely.

Q What is supercriticaJ CO2?

A When we bring CO2 up to a certain pressureand temperature, it becomes what is called asupercritical fluid. It behaves a little like a liquidand a little like a gas, so it is able to do the jobwe need it to do. Other researchers have alreadyused CO2 in its supercritical state to extractunwanted organic compounds from soil. Theidea of using it to remove metals was firstproposed around 1991. Our lab is one of onlya handful in Canada that are pursuing the idea.

Q What does the cleaning process entail?

A A batch of contaminated soil is closed

inside a reactor, along with something called

a "chelating agent." CO2 is pumped in, and the

pressure and temperature within the reactor are

set. The supercritical fluid remains in contact

with the soil for several minutes or hours.The blue colour in this soil is due to contamination by toxic metals.

130 MHR . Unit Ener~ and Matter in Chemical Change

The length of time depends on the amount ofsoil and the metal that is being removed. Whenthe CO2 is removed, depressurized, and broughtto normal temperature, it changes from itssupercritical fluid state back to a gas. Then themetal deposits just fallout of it. We're left withCO2, which is recycled. We're also left witha small amount of highly concentrated metal,which we hope we can recycle some day.

Q How exactly does the CO2 get the metal to leave the soil?

A The metal is usually in the soil in the form of acharged ion. Carbon dioxide is not charged. Sothe metal won't dissolve in CO2 on its own. That'swhy we add the chelating agent. If the right chelateis added, the metal bonds with the chelate morethan with whatever it is bonded to in the soil.Once the metal combines with the chelate, thecompound has no charge. The compounddissolves in the CO2 and flows out with it.

Q What sort of metals can you extract using this process?

A We've been using copper as our test metal.Once the process has been perfected, we hopeto use it to remove such things as lead, mercury,cadmium, and chromium. One day, far down theroad. it may even remove radioactive elements.

Q What stage is your research at right now?

A My students and I are beginning to work on

designing a way to pump new batches of soil into

the reactor without having to depressurize in

between. The depressurizing and repressurizing

for each load of soil is one of the most expensive

parts of the process right now. For the moment,

however, our research is focussed on determining

the best chelating agent to use. We hope to do

some trials with soil samples in the near future.

A soil-cleaning reactor

~ ,

. " ,I 1

! Personal Poisons: Removing Metals surrounding chelation therapy, what are the view- :: from the Blood points, and what is being done to resolve them? :

: . As a starting point, go to www.mcgrawhill.ca/ I

1 Many of the same tOXIC, heavy metals that contam- I. k / . f 10 :I .. . . In s science ocus . 1I Inate soil, water, and air are often found In the II I: bloodstream of people who have been exposed: to these contaminants. Lead and mercury areI: especially worrisome, because they directly and: indirectly cause a host of serious (and sometimes11 deadly) health problems. Anyone can be exposed1: to lead. Common sources include old paint, soil,: and even some toys. Sources of mercury include: old paint, some kinds of fish, and certain vaccinesI: and drugs prepared prior to the late 1990s. Chelation: therapy is a proven course of action for removing --- I

: heavy metals from blood. What is this therapy, and Is there lead or other heavy metals contaminating this site? :: what does it involve? Why are there controversies Why does it matter? How could you find out? :I I

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Unit 1 Ask an Expert. MHR 131

Some suggested areas of investigation:. Does every antacid tablet of the same brand

contain the same quantity of active ingredient?. How do antacid tablets of different brands compare

in terms of neutralizing ability? What does this haveto do with the mass of the tablets or the nature ofthe active ingredient?

. Do antacid tablets of different brands contain thesame active ingredient? If not, how could youcompare the effectiveness of different brands?. What are the products of the reaction betweenan antacid and an acid? (Can you isolate andtest any or all of these products?)

Think About ItOne of the most significant of all chemical reactionsoccurs inside your body. It is probably occurring rightnow. If not, it will as soon as you have your next mealor snack. Chemical reactions change the food you eatinto compounds that your body uses to grow, maintainand repair cells and tissues, and provide energy. Thesereactions are collectively known as digestion.

The stomach is one of several organs involved indigestion. It secretes an acid - hydrochloric acid, widIa pH of 1 or 2 - that helps break down food particles

and large nutrient molecules. When you eat a largemeal, dIe stomach secretes more acid to assist withthis process. The excess acid can cause a condition youhave probably seen or heard advertised: heartburn(or acid indigestion). It occurs when dIe acidicstomach contents are pushed into the lower areaof dIe esophagus. The esophagus does not havea protective lining like the stomach does, so youfeel a burning sensation in your throat and chest.

For immediate relief of heartburn, many peoplereach for an antacid product. What kind of chemicalsdo antacid products contain? Which is dIe activeingredient, and what kind of chemical reaction doesit produce? Are dIere effective alternatives to store-bought antacid products? What oilier questions aboutantacids can be asked? In this investigation, you andyour team members will study one aspect of antacids.Formulate a question based on information you havestudied in this unit and information you may find byresearching on dIe Internet. Then decide how you willcarry out an experiment to answer your question. Besure to have your teacher approve your materialsand procedure before you begin. The followingsuggestions will give you some ideas.

Possible methods of investigation:. Is a gas produced by the reaction you are working

with? If so, how can you use what you know aboutthe law of conservation of mass? What can youdetermine by comparing the mass of the reactionvessel and contents before and after the reaction?

. Does a neutralization reaction take place? If so, howcan you use indicators and drop by drop titrationto compare the effectiveness of active ingredientsin antacids?

Safety Precautions ~ n ICJ ~. Do not mix chemicals without your teacher's

knowledge and approval.. You will be working with dilute acids and/or bases in

this investigation. Remember that bases and acids arecorrosive. If any acid or base contacts your skin, rinsethe area with plenty of cold water and inform yourteacher. Clean up any spills as your teacher directs.

. List additional appropriate safety precautions asyou design your experiment.

For tips on how to set up a controlled experiment, turn toSkill Focus 6.

132 MHR . Unit Energy and Matter in Chemical Change

MaterialsBrainstorm a list of the apparatus and materials thatwill be most appropriate to answer your question. Youmay also need electronic resources, constructionmaterials, and art materials for your final report.

. Write up your findings in a laboratory report.Be sure to include the following:. Introduction

. Hypothesis and/or prediction

. Procedure (step by step), including a diagram

. Data/Observations in the form of words

combined with graphs, tables, etc.. Conclusions

Initiate and Plan.0 With your group, decide on an experimental

question to investigate. You might need to dofurther research to decide on the question.

. If it is appropriate to your question, formulatea hypothesis that provides an explanation thatrelates to your question. Write a testableprediction that states what you think youwill observe in your particular experiment.

(D) Evaluate your experimental design.

(a) How would you change your design if youwere going to perform the experiment again?

(b) What further questions arose as you carriedout your experiment? How might youinvestigate these questions?. Brainstorm ways to test your prediction. Any

of the lab skills you have learned in this unit andin earlier courses may be useful. For example,you may have experimented with acid-baseneutralization in Grade 9.

G Design an experiment to test your prediction.Use words and diagrams to explain your design.Refer to the Experimental Design Checklist onthe right for help.

Perform and Record(Test Your Prediction)8 Set up and perform your experiment. Carry out

two or more trials. Make modifications to yourexperiment as necessary.

e Gather and record data and observations as youconduct your experiment. Decide how to recordand present your data in a clear format.

Analyze and Interpret(Draw Conclusions). Draw conclusions based on the results of your

experiment. Discuss your conclusions with

your group.

0 Did your findings agree with your prediction?Are you able to use your hypothesis to explainyour results? Explain.

Unit 1 Design Your Own Investigation. MHR 133

Now that you have completed Chapters 1, 2, and 3,you can assess how much you have learned byanswering the following questions. Before youbegin, you may find it useful to return to eachChapter at a Glance and each Chapter Review.

13. A compound containing only two elementsis called a .

14. In forming an ionic compound, a calcium atomtends to transfer to an atom ofa element.

15. In a weak acid, a proportion ofacid molecules in solution.

True/FalseIn your notebook, indicate whether each statementis true or false. Correct each false statement.

16. Neutralization is an example of a1. Ernest Rutherford provided evidence for the elec-

tron by bombarding gold foil with alpha particles.17. The reaction of sodium with water is an example

of a reaction.2. An anion has more electrons than protons.

3. The atoms in diatomic molecules are heldtogether by ionic bonds.

18. When methane, CH4(g), burns in sufficientoxygen, the reaction is called areaction.

4. Metals usually react to form cations, not anions.19. Incomplete combustion of hydrocarbons

results in the production of a toxic gas called5. All binary ionic compounds containing

the sodium ion are soluble in water.

6. Burning propane is an example of anendothermic reaction.

20. One mole ofcarbon-12 atoms has a mass ofexacdy .

7. In a decomposition reaction, two or moresubstances react to produce one substance.

8. A sample of water containing 6.02 X 1023molecules has a mass of 36 g.

9. One mole of iron, Fe, has a mass of55.85 g.

10. One mole of molecular oxygen, 02(g) contains6.02 X 1023 atoms of oxygen.

CompletionIn your notebook, complete each statement with thecorrect term or phrase.

Matching21. In your notebook, copy me following descriptions.

Beside each description, write me tenn from mebulleted list mat best fits me description. A tennmay be used once, more man once, or not at all.

(a) common name of a strong acid

(b) reaction mat absorbs energy from its

surroundings(c) group of atoms wim a net charge; me

atoms are joined by covalent bonds

(d) type of bond mat fonns between twonon-metal atoms

(e) type of bond in a molecule of oxygen, 02

(f) unit for me amount of a substance

(g) intermolecular bonds in water

11. J.J. Thomson observed me behaviour ofproduced in gas discharge tubes to

provide evidence for me existence of .

12. Bohr's theory of the atom says that electronshave certain allowed energies called


Short Answer26. Give two examples of anions that have the same

number of electrons as neon, N e.

. ionic bond

. vinegar

. endothermic

. polyatomic ion

. muriatic acid

. covalent bond

. mole (mol)

. gram (g)

. hydrogen bond27. Draw electron dot diagrams to represent an atom

of each of the following:

(a) silicon (c) strontium

(b) sulfur (d) argon

28. Draw electron dot diagrams for each of thefollowing pairs of elements. Then show howatoms of each pair could form a compound,and predict the formula of the compound.

(a) Si and H (c) Ca and N

(b) Be and 0 (d) AI and P

29. Name the following compounds.

(a) Fe2(SO4)3(s) (c) SO3(g)(b) Pb(NO3)4(s) (d)HI(g)

Multiple ChoiceIn your notebook, write the letter of the best answerfor each of the following questions.

22. Which of the following is not a typical propertyof an ionic compound?

(a) Ionic crystals with a well-defined shape format room temperature.

(b) Aqueous solutions of ionic compounds aregood electrical conductors.

(c) Ionic solids conduct electricity.

(d) Ionic solids have relatively high melting points.

(e) Ionic solids are hard and brittle.

23. What are the fonnulas of the carbonate ion,the ammonium ion, and the nitrate ion?

(a) CO32-, NH3+, and NO3+

(b) CO32-, NH3 +, and NO32-

(c) CO3-, NH4+, and NO3-

(d) CO32-, ~+, and NO3-

(e) CO23-, ~+, and NO32-

30. Write formulas for the following compounds.

(a) copper(I) nitrate

(b) mercury(II) bromide

(c) nickel(III) sulfide

(d) calcium hydrogencarbonate

31. Write the molar mass of each of thefollowing elements.(a) sodium, Na (c) silicon, Si(b) barium, Ba (d) iodine, 12

32. Predict whether each of the following ioniccompounds are soluble or insoluble in water.

(a) Ba(CIO3)2(s) (c) SrSO4(s)

(b) NaCH3COO(s) (d) ~OH(s)

24. When the following equation is balanced,what is the value of x?

wAl + XH2S04 -7 yAl2(SO4)3 + ZH2

(a) 1 (d) 4

(b) 2 (e) 5

(c) 3

33. What is the range of pH values for an acid?25. Which of the following ionic compounds ishighly soluble?

(a) AgzSO4(s) (d) Ca(OH)z(s)(b) PbClz(s) (e) Ba(OH)z(s)(c) CuCl(s)

34. Draw a concept map to explain how the averageatomic mass of an element and its molar massare related.

Unit 1 Review. MHR 135

3 S. Explain how the law of conservation of mass isreflected in the coefficients in balanced chemicalequations. Use an equation to illustrate

your explanation.

36. Why do many household cleaning productscarry warning labels? Why should you weargloves when using an oven cleaner?

37. Explain why water is a polar molecule.

38. Choose two unusual properties of water.

(a) State what practical consequence eachproperty has.

(b) Explain each property based on thestructure of the water molecule.

(b) NaOH(aq) + ~)2S04(aq)-?

Na2S04(aq) + NH3(g) + H20(f)

(c) H2S04(aq) + Al203(s) -?Al2(SO4)3(aq) + H20(f)

(d) Zn(s) + FeCI2(aq) -? ZnCI2(aq) + Fe(s)

(e) C3H4(g) + H2(g) -? C3Hs(g)

(f) CaCO3(s) + HCI(aq) -?CaCI2(aq) + H20(f) + CO2(g)

41. Determine the molar mass of each of the

following compounds.(a) chlorine dioxide, CIO2(g)

(b) disulfur dichloride, S2CI2(g)

(c) sodium nitrate, NaNO3(s)

(d) phosphorus pentabromide, PBrS(f)

(e) urea, C~20(s)

(f) iron(Il) phosphate, Fe3(PO4)2(s)

42. How many moles of each substance are in eachof the following samples?

(a) 34.1 g Au(s)

(b) 1.08 g Cr203(s)

(c) 4.33 X 10-2 g NH4Br(s)

(d) 3.32 kg (NH4)2Cr207(s)

43. What is the mass of each of the following?

(a) 3.70 mol HzO(t')

(b) 14.8 mol BaCrO4(s)

(c) 2 X 103 mol HC!(g)

(d) 0.0345 mol FeZO3(s)

44. How many molecules of CO2(g) are in 2 molof CO2(g)?

Problem Solving! Applying39. Copy each of the following word equations into

your notebook. Then write the balanced chemicalequation, and classify the reaction.

(a) Sodium reacts with water to produce aqueoussodium hydroxide and hydrogen gas.

(b) Solid magnesium oxide reacts with carbondioxide to form magnesium carbonate.

(c) When heated, solid ammonium chlorideforms ammonia and hydrogen chloride gas.

(d) Aqueous copper(I1) sulfate reacts with solidnickel to form aqueous nickel(I1) sulfate andcopper metal.

(e) Solid sodium carbonate reacts with sulfuricacid to form an aqueous solution of sodiumsulfate, water, and carbon dioxide gas.

(f) Ammonia gas reacts with hydrogen chloridegas to form solid ammonium chloride.

40. Copy each of the following skeleton equationsinto your notebook. Then balance the equationand indicate the type of reaction.

(a) NaCIO3(s) ~ NaCI(s) + 02(g)

45. Suppose you had an oven that could reachextremely high temperatures. If you place a sampleof malachite in the oven and heat it vigorously,would you expect to obtain copper? (The ovenis made of an unreactive material.) Explainyour answer.

136 MHR . Unit 1 Energy and Matter in .Chemical Change

(e) Suggest a way you could test if a breakfastcereal contained elemental iron withoutlooking at the list of ingredients.

46. Alloys of titanium with iron are used in airplanesand racing bicycles because of their strength andrelatively low density. Titanium can be obtainedby reacting TiC4 at a high temperature withmagnesium. The skeleton equation is:

TiCI4(g) + Mg(t') ~ Ti(s) + MgCI2(t')

(a) What is an alloy?

(b) Balance the equation and classify the reaction.

(c) At the temperature of the reaction, whichmetal has the higher melting point? Explain.

49. Hemoglobin is a protein molecule in blood thatcarries oxygen to all of the cells of the body.Carbon monoxide is produced by the incompletecombustion of fuels. It is a poison because it canbind to hemoglobin in the place of oxygen, witha bond that is almost 200 times stronger than thehemoglobin-oxygen bond. If a person is workingin the presence of carbon monoxide, poisoningmay result.

(a) Based on the information above, how mighta person with carbon monoxide poisoningbe treated?

(b) Suggest at least two situations that wouldcreate a risk for carbon monoxide ~

poisoning, and suggest ways to avoid orremedy those situations.

Critical Thinking47. A student carries out a chemical reaction in the

laboratory that generates a gas. The studentdecides to test the gas to identify it. The studentlowers a burning splint into the gas, and theflame is immediately extinguished. The studentconcludes that the reaction produced the gascarbon dioxide. Do you agree with this conclusion?If so, explain why. If not, what other tests couldyou carry out to positively identify the gas?

48. The RNI (recommended nutrient intake) ofiron for women is 0.0148 g per day. Ferrousgluconate, Fe(C6lIIIO7)2(s), is often used in ironsupplements because it is easier than elementaliron for the body to absorb. Some iron-fortifiedbreakfast cereals contain elemental iron metalas their source of iron.

(a) Determine the number of moles of elementaliron, Fe, required by a woman each dayaccording to the RNI.

(b) Determine the molar mass of ferrous gluconate.

(c) What mass of ferrous gluconate would satisfythe RNI for iron?

(d) Some evidence suggests that the elementaliron in iron-fortified breakfast cereals isabsorbed only to a small extent. How coulda breakfast cereal manufacturer assure thata consumer absorbs more iron? Make twosuggestions, and list the pros and cons ofeach suggestion.

so. Mercury is highly toxic in its elemental formand in chemical compounds. Water-solublemercury compounds such as mercury(II) nitrate,Hg(NO3)Z(s), are particularly dangerous, becausethey are easily spread through an ecosystem viawastewater. One way to remove mercury(II)nitrate from wastewater is to add sodium

sulfate, NazS(s).(a) Predict what reaction will occur when

mercury(II) nitrate and sodium sulfatereact in aqueous solution. Write a balancedequation for the reaction and classifythe reaction.

(b) Explain why this reaction would be usefulas part of a process for removing mercuryfrom wastewater.

(c) What would likely be the next step in the

clean-up process?

Unit 1 Review. MHR 137

Documents

DidYouKnow?, When you buy a carton that says it contains one …€¦ · DidYouKnow?, The Mole For convenience, chemists group particles by large numbers that are easier to work with