topic 8 reaction rate

Reaction RateChemical reactions can occur at different speeds (See Figures 2.58 A,B, and C). Why does one reaction take longer than another? Can youmeasure the speed of a chemical reaction? Can you slow down or speedup a chemical reaction?

The reaction rate is a measure of how fast a reaction occurs. To findthe rate of reaction, you can measure either how quickly one of thereactants is disappearing or how quickly one of the products is appear-ing. Both measurements show how the amount of a substance changesper unit of time.

The rate of a chemical reaction can be speeded up or slowed down bychanging the temperature. At higher temperatures the rate of most chemi-cal reactions increases. Faster-moving molecules and atoms collide morefrequently and therefore can form new substances more quickly. For exam-ple, the high temperature inside an oven speeds up the chemical reactionsthat change the liquid batter into a cake. Fresh fruit and vegetables areoften kept in the refrigerator to slow down the chemical reactions.

Other ways of changing the rate of reactions include stirring and chang-ing the size or the concentration of the reactants. Stirring a cake batter willspeed up the reaction rate. If you grind up a chemical before mixing it,there will be more surface area for the chemical reaction. If you increasethe concentration of a substance, you will increase the number of particlesof a substance per unit of volume.

Reaction Rate •MHR 153

T O P I C 8

Figure 2.58A To speed up this reaction,ammonium nitrate has been ground into apowder and heated to a high temperature.

Figure 2.58B How could you speedup the reaction rate for a banana toripen? How could you slow down thereaction rate?

Figure 2.58C How long do you think ithas taken for carbonic acid to dissolvelimestone and form this cave?

154 MHR • Matter and Chemical Change

Find OutChanging with the TimesHow can you speed up or slow down a chemical reaction?

Procedure

Do not perform the reactions shown in the table. Read the description of each trial. Think aboutthe effect of the change in conditions on the rate of each reaction.

Chemical reaction Trial 1 Trial 2A. Calcite reacts with The calcite is in large pieces The calcite is in small pieces

hydrochloric acid

B. Sulfuric acid reacts with The acid is a 5% solution The acid is a 10% solutionthe lead in a car battery

C. NaOH(aq) � HCl(aq) The reactants are stirred The reactants are not stirred➞ NaCl(aq) � H2O(l)

D. An iron nail reacts with a The reaction takes place at The reaction takes place at solution of copper (II) 65°C 25°Csulfate

1. Predict which reactions would be faster in thesecond trial. Explain.

2. Predict which reactions would be slower inthe second trial. Explain.

What Did You Find Out?

1. What additional changes could be made in chemical reaction A if you wanted toincrease the speed of the reaction?

2. What could be done to slow down the chemical reaction in reaction B?

3. Write a word equation describing the chemical reaction in C.

Extensions

4. What are two advantages to increasing the reaction rate for reactions? Give anexample for each.

5. What are two advantages to decreasing the reaction rate for reactions? Give anexample for each.

Analyzing and Interpreting

The Right Mix

Years ago, pharmacists ground up and mixed together the ingredients of many prescriptionsthemselves. Even though prescriptions these days come ready-mixed from pharmaceuticalcompanies, pharmacists like Ginette Goulet still need to know about reaction rates.

Ginette has to know which combinations of prescription drugs and other factors can affectchemical reactions and cause problems for the patient. She lets her customers know, forexample, if the prescription they receive should not be taken with milk, or if it should be tak-en on an empty stomach to be most effective. She also lets them know if certain “over-the-counter” drugs, such as antihistamines, should not be taken until they have finished thecourse of their prescription. Since some customers may be on more than one prescriptionat the same time, she needs to know which drugs can be taken safely together, so that thereare no conflicts between the prescribed drugs.

Speeding Up a Reaction with CatalystsAnother way to change the rate of a reaction is to add orremove a substance called a catalyst. A catalyst is a substancethat speeds up the rate of a reaction without being changeditself. A catalyst does not affect the amount of product pro-duced in a chemical reaction. A catalyst increases only the speedof the reaction.

An enzyme is a natural catalyst made by living things. Almostall chemical reactions that take place in the body are catalyzedby enzymes. When you chew a piece of bread, glands in yourmouth produce saliva, which contains an enzyme (see Figure2.57). The enzyme in saliva acts as a catalyst to help break downstarches into smaller molecules. When you get a foreign particlein your eye, an enzyme in your tears attacks the cell walls ofbacteria, preventing them from infecting the eye.

Many other chemical reactions depend on catalysts to helpthem work faster. For example, the production of vegetableshortening, synthetic rubber, and high-octane gasoline are allchemical processes that succeed with the help of catalysts. Some laundry detergents contain enzymes that break down the proteins responsible for many stains in clothing.

You will examine the effects of a catalyst in the next investigation.

Slowing Down a Reaction with InhibitorsSuppose you wanted to slow down the rate of a chemical reaction.What could you do? You could add an inhibitor. Inhibitors aresubstances that slow down chemical reactions. For example,some plants have natural inhibitors in their seeds to preventgermination until conditions are just right. Inhibitors are addedto some foods and medicines to slow down their decomposition.

In the last investiga-tion you observed thathydrogen peroxidedecomposes to formoxygen and water (seeFigure 2.58). Aninhibitor is added tobottles of hydrogen per-oxide to prevent its mol-ecules from decompos-ing too quickly.


Salivary glands

Esophagus

Tongue

Figure 2.57 As you chew your food, thesalivary glands in your mouth release anenzyme. The enzyme speeds up thebreakdown of food.

A chemical reaction is proceedingat a rate of 4 g of product producedevery 30 s. How many minutes willit take to obtain 80 g of the productfrom the reaction?

Figure 2.58 Hydrogen peroxide helps todisinfect wounds. Which gas is beingproduced in this picture?

One of the most importantgroups of enzymes are the proteases. The proteases breakdown proteins. Proteases areused in many common products,such as meat tenderizers andcontact lens cleaning solution.Proteins secreted by the cellsaround the eyes build up oncontact lenses. Proteases in thecleaning solution help to removethe proteins. Sometimes peoplehave deficiencies in certainenzymes. Research “lactoseintolerance” on the Internet or at the library. Find out whichenzyme is missing in peoplewho have this condition.

2-H2-H


Reaction TimeThe compound hydrogen peroxide will slowly decompose into water and oxygen ifleft in an open container.

2H2O2(aq) —-> 2H2O(l) + O2(g)

QuestionWhat will happen to the decomposition time of hydrogen peroxide if a catalyst is added?

HypothesisFormulate a hypothesis about how the addition of a catalyst affectsthe decomposition of hydrogen peroxide.

Safety Precautions

• Hydrogen peroxide can irritateyour eyes and skin. Be sure towear protective equipment. Donot use more than 5 mL of 3%hydrogen peroxide in each testtube.

• If you accidentally spill hydrogenperoxide on your skin, wash it offwith lots of cool water.

• Use caution with hot objects.

• Before striking matches, checkthat there are no flammablesolvents nearby.

Apparatus 600 mL beakerhot plate 2 test tubesgraduated cylinder (10 mL)test tube racktest tube tongsmetric measuring spoons

Materialswater3% hydrogen peroxidemanganese dioxidewooden splintsmatches

ProcedureMake an observation chartlike the one below.

Add 300 mL water to thebeaker. Place the beaker ona hot plate. Turn the hotplate to medium power.

Put two test tubes in the testtube rack. Label the testtubes A and B.

Pour 5 mL 3% hydrogenperoxide into each of twotest tubes.

Place 2 mL manganesedioxide in test tube A.Record your observations.

Light a wooden splint. Blowout the flame and quicklyinsert the glowing splint intoeach test tube. Do not letthe splint touch the liquid.Record your observations.

Place both test tubes in thehot water bath. Heat thetest tubes until all of theliquid in both test tubeshas evaporated.

Remove the test tubes fromthe hot water bath. Recordyour observations.

Repeat step 6.

Turn off the hot plate. Returnall equipment to the properlocation. Wash your hands.

S K I L L C H E C K

Initiating and Planning

Performing and Recording


Communication and Teamwork

ObservationsTest tube Before heating After heatingA

B


Analyze1. Describe what happened when the man-

ganese dioxide was added to test tube A.

2. What gas was produced in the test tube withmanganese dioxide? How do you know?

3. In which test tube did the reaction occurmore quickly? How do you know?

4. What remained in the test tubes at the endof the procedures?

Conclude and Apply5. What is the function of the manganese

dioxide? Give reasons for your answer.

6. How could you make this experiment morequantitative and make more accurate mea-surements?

Extensions7. In the photograph below, sugar has been

added to a carbonated beverage. Explainwhat has happened.

8. Construct a model that shows the decompo-sition of 2H2O2(aq) into 2H2O(l) and O2(g).

Electronic equipment isusually packaged withsmall packets of silica gel.Silica gel is a desiccant.Desiccants absorb watervapour from the air. Whatchemical reaction is silicagel helping to prevent?What else will a dryer environment help prevent?Which other products arepackaged with silica gel?

CorrosionWhat happens to some metals when they are exposed toair and moisture? The metals undergo a chemical reactionand gradually corrode. Corrosion is the oxidation of met-als or rocks in the presence of air and moisture. You maybe familiar with one type of corrosion: rust. Rust is ironoxide, a product of the chemical reaction of iron, oxygen,and moisture. One equation for corrosion is shown below:

4Fe(s) + 3O2(g) → 2Fe2O3(s)(iron) (oxygen) (iron oxide)

Take a closer look at corrosion in the next activity.


Find OutCorrosion CollectionWhat role does a gas play in the process ofcorrosion?

Materialsgas collecting bottles pie plate or dishsteel wool grease pencils or tapevinegar water

Procedure

1. Clean the steel wool by dipping it in thevinegar.

2. Pack the steel wool tightly in the bottom ofthe gas collecting bottle so it will not fallout when the bottle is inverted.

3. Fill the pie plate or dish two thirds full withwater. Invert the gas collecting bottle con-taining the steel wool in the pie plate.

4. Mark the starting level of water in the gascollecting bottle with masking tape or agrease pencil.

5. Observe for at least two weeks. Every fivedays mark the level of water in the gas col-lecting bottle and add more water to thepie plate.


1. What happened to the level of water inthe gas collecting bottle when you firstinverted it in the pie plate? Over a periodof two weeks?

2. Why did you invert the bottle in the water?

3. Did a chemical or physical reaction takeplace? How do you know?

4. List the products and reactants of thisreaction.

5. What gas is needed for corrosion to takeplace? What part of your experimenthelped you make this inference?

Extensions

6. How could you have increased the reactionrate? How could you have decreased thereaction rate?

7. Make an inference as to how much of theatmosphere is composed of oxygen. Usethe results of your experiment to makethis inference.


Figure 2.59 Iron combines withpure oxygen in the flask to formiron oxide. This is the samereaction as the rusting of iron,but happens much faster.



Preventing CorrosionCorroded materials lose their strength. Once the top layer ofmetal has corroded, more surface area is exposed. Oxygenfrom the air can then reach the inner layers. Corrosion alsooccurs at points of strain in the metal. Rust will eventuallymake its way through the metal, and the object will be com-pletely corroded.

One way to protect a metal from corrosion is to apply a thincoating of paint. Another way to protect a metal is to coat itwith zinc, which is more resistant to corrosion. The process ofcoating metals with a thin layer of zinc is called galvanization.What are some examples of galvanized products? Houses andbuildings under construction are exposed to moisture and air,which could corrode the metal parts before the building iscomplete. If the nails and other metal parts are galvanized,then corrosion is not a serious problem.

Other metals can also be used as a covering to prevent rust.Some car bumpers are coated with a thin layer of chromiumto protect the iron from corroding. The process of covering ametal with another metal by using electrolysis is called elec-troplating. Chromium is often electroplated onto a softermetal to improve its hardness, stability, and appearance.

CombustionCombustion is the highly exothermic combination of a substance withoxygen. Combustion requires heat, oxygen, and fuel. You may be familiarwith the burning that takes place in a fireplace, a gas barbecue, or the fur-nace in your home. Did you know that combustion also takes place insidethe internal combustion engine in a car? Gasoline combines with oxygento release energy to make thecar move. Every time some-thing burns, it combines withoxygen from the air. Even thefood you eat is converted toenergy by combining with theoxygen that you breathe. Youwill investigate reactants andproducts of combustion in thenext investigation.

Figure 2.60 The surface of a can thatcontains iron corrodes quickly outdoors. Therust formed on the surface of the can flakesoff easily, so the can continues to corrode.The surface of an aluminum can oxidizesvery quickly. The aluminum oxide formedmakes a tough protective layer, which doesnot flake off easily. Therefore, aluminumcans will take over 400 years to degrade.How can you tell that most of the cans inthis picture contain iron?

Figure 2.61 How is enough heat produced to melt metal? The combustion reaction of acetylene and oxygen is

2C2H2(g) � 5O2(g) → 4CO2(g) � 2H2O(g) � energy

There are several formsof iron oxide, each withinteresting, observableproperties. Iron (II) oxidesometimes ignites spon-taneously in air. Iron (III)oxide is called hematite,and is reddish brown incolour. Rouge is a spe-cially purified form ofiron (III) oxide, andVenetian red, which islargely iron (III) oxide,has been used to paintbridges, barns, and out-door structures.

An Illuminating ExperienceIn this investigation you will investigate the products of combustion. The investi-gation is divided into three parts. Be sure to keep accurate records of the results ofeach part of the experiment.

QuestionWhat are the products of the combustion of a candle?

HypothesisFormulate a hypothesis about what the reactants and products are in the combustion of a candle.

Safety Precautions

• Before lighting candles, makesure there are no flammablesolvents nearby.

• Use care with matches.

Apparatustray for water (15 cm x 20 cm)gas-collecting bottle or glass jarevaporating dishall-purpose tongs

Materialsmatchescandle (10 cm x 1 cm diameter)ice cubesaluminum foilwater

ProcedureMake an observation chartsimilar to the one shownbelow.

Part 1Light the candle. Use a fewdrops of candle wax tosecure the candle to themiddle of the tray. Fill thetray two-thirds full of water.

While the candle is stillburning, lower the invertedgas-collecting bottle or jar

over the candle. Carefullyobserve what happens bothto the candle and the level ofwater in the bottle.

Record observations onyour chart and make infer-ences as to what happened.

Part 2Light the candle.

Place an ice cube in theheat-resistant evaporatingdish. Hold the evaporatingdish with the all-purposetongs over the burning can-dle for 10 s.

Record your observations.There should be at least twosignificant observations.

2-I2-I


S K I L L C H E C K

Initiating and Planning




Investigation Observations InferencesPart 1

Part 2

Part 3

Heat-resistant,wide-mouth gascollecting bottle

Burning candle

Tray, such as a glass

pie dish

Water

Part 3Cut a piece of aluminum foil in a circle thathas a diameter of approximately 22 cm. Foldthe circle of foil in half, and in half again. Cuta small hole at the corner where all folds meet.Open the foil to make a large cone with a holein the middle.

Hold the cone with the all-purpose tongs andplace it over the burning candle with the holenear the top of the flame. Be careful not toextinguish the flame.

Light a match. Hold it over the hole in thealuminum foil that is being held over the burn-ing candle. Be careful not to burn yourself.

Observe and record your observations.


Analyze1. What are the products of the combustion

of a candle? What evidence supports youranswer?

2. Which product(s) of combustion are mostimportant to your daily life? Why?

3. Which part of the experiment illustratesone of the reactants needed for combustion?What is the reactant?

4. Which safety precautions did you followwhile working near an open flame? Howcould you improve your awareness of safetyduring investigations?

Conclude and Apply5. What is the chemical name and formula

for the black substance found on the bottom of the evaporating dish in Part 2?Where could the black substance havecome from? Explain.

6. Research on the Internet or in the libraryand write the chemical equation for thecombustion of gasoline in an automobile.(Hint: The organic compound octane isfound in gasoline.)


Products of CombustionYou have just investigated the products in the combustion of a candle.Another chemical reaction involving combustion occurs when propaneis burned in a barbecue. Burning propane is an exothermic reactionthat produces heat to cook the food. When the heat becomes toointense, sometimes the organic compounds in the meat or vegetablesare chemically changed to pure carbon as seen by the black coating.The equation for the combustion of propane is shown below:

C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) + energy (heat)propane + oxygen → carbon dioxide + water + energy (heat)

Compare the equation for the combustion of propane with the equa-tion for the combustion of methane on page 149.

The products of combustion are not always beneficial. Burning woodor coal produces smoke and ash as well as heat. In addition, other sub-stances are created by combustion. Soot, carbon monoxide, carbondioxide, and oxides of sulfur and nitrogen can be created by the com-

bustion of fuels such as coal, gas, andoil. Some products created when fuel isburned are pollutants. The brown hazethat hangs over some cities is smog (seeFigure 2.62). Smog is created when sun-light reacts with pollutant chemicalsproduced by burning fuels. You willlearn more about pollution in Unit 3,Environmental Chemistry.

In the next activity you will observeseveral chemical reactions involvingcombustion.

Figures 2.64A and B Burning methane and propaneare examples of combustion reactions. Methane isthe main component in natural gas and propane issometimes used in barbecues.

Figure 2.63 Coal is achemical mixture of carbon,sulfur, and other elements.Which element do yousuppose is burning in thispicture? Which chemicalreaction is occurring while thecoal is burning?

Figure 2.62 Tiny particlesof soot suspended in theair reduce visibility. Theseparticles irritate the eyesand respiratory system.

Methane CH4H

H

C HH

Propane C3H8H

H

CH H

H

H

C

H

H

C


Find OutWhere’s the Fire?Combustion can be a simple or complex reac-tion. In this activity you are going to study afew simple reactions involving combustion. Besure to place used matches, burned wood,and marshmallows in the appropriate wastecontainer provided by the teacher.

Safety Precautions

• Before striking a match, make sure there areno flammable solvents nearby.

• Use care with matches and burning materials.

Materials

2 wooden splintsevaporating dishwaxtoothpickminiature marshmallowwatch glassmatchessugar cube

Procedure

1. Prepare an observation chart to collectyour data and observations.

2. Light a wooden splint and observe thechemical reaction of the burning of thewood. Brainstorm with your group and seeif you can write a word equation for thereaction you have just seen.

3. Break up a second wooden splint intosmall pieces and set them in an evaporat-ing dish. Light the bits of broken splint.How does this reaction compare with thefirst splint you burned? Keep the ash foruse later in this Find Out Activity.

4. Place a small piece of wax on a watch glass.Use a match to try to light the wax and makeit burn. What happens?

5. Place a toothpick in a piece of wax to useas a wick. Light the toothpick and observe.Record your observations.

6. Place a marshmallow on a watch glass.Light the marshmallow with a match.Observe the reaction and record.

7. Place a cube of sugar on a watch glass.Try to light the sugar cube. Observe andrecord the results. Add a small amount ofwood ash from your wooden splint fire tothe sugar cube. Try to light the ash. Recordyour observations.


1. Write a word equation for the reaction youobserved when you burned the wood.

2. Why were you not able to light the wax byitself or with the toothpick? (Hint: You areable to light candles made of wax.)

3. What are the products of combustion of amarshmallow?

4. What products are always made duringcombustion? How do you know?

5. What was the purpose of the ash youadded to the sugar?

6. Describe the difference in burning times insteps 2 and 3. Explain why there was a dif-ference.




1. List five ways you could increase the rate of a chemical reaction.

2. List five ways you could decrease the rate of a chemical reaction.

3. Explain the differences between the terms in each of the following pairs of words:(a) reactant, product(b) catalyst, inhibitor(c) chemical reaction, rate of reaction

4. In your own words, describe the effects of the following factorson the rate of a chemical reaction.(a) concentration(b) surface area(c) temperature

5. State a word equation for corrosion.

6. Describe the process of galvanization. Why are some metalproducts, such as nails and bolts, galvanized?

7. Why does a candle burn longer in the open than under an inverted glass jar?

8. What are some of the beneficial and harmful effects of burning fuels?

9. Thinking Critically Describe the similarities and differencesbetween combustion and corrosion.

164 MHR • Matter and Chemical Change164 MHR • Matter and Chemical Change

T O P I C 8 Review

Virtual reality is the simulation of a real environment created byadvanced technology. Headsets containing small screens can beused to view chemicals. Some chemists use cyberspace tobuild new compounds as shown in the picture to the right. Thelarge purple ribbon-like molecule is an enzyme, while the blue isa DNA molecule. Chemists also use computers to predict theoutcome of chemical reactions and the effect of catalysts.Computers provide a safe alternative starting point for the moredangerous experiments.

Articles on board the Titanic spentmany years in seawater before theywere brought to the surface. Manywere covered with corroded met-als, sand, and other chemicals.Chemistry helped to restore theseitems. Electrolysis and anotherprocess, called electrophoresis,were used to remove the corrosionfrom leather, bank notes, and thesecasserole dishes. Electrophoresisis a technique of separating ions.The artifact is placed in an elec-trolyte solution and a current isapplied. The current breaks up thedirt, salts, and other corrodedmaterials as the particles move tothe electrodes.

If you need to check an item, Topic numbers are provided in brackets below.

Key Terms

Reviewing Key Terms1. Copy the crossword puzzle into your note-

book, or use the one provided by yourteacher. Use the hints and terms that followto complete the puzzle. (7–8)

Understanding Key Concepts2. Is the following reaction endothermic or

exothermic? How do you know? (7)

2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g) + energy

3. If you wanted to slow down a chemical reaction,what could you add? Give several examples. (8)

4. Give examples of three things that affect therate of a chemical reaction. (8)

5. If you add a chemical to a test tube and thetest tube becomes warmer, what can youinfer? Give two different inferences. (7)

6. Apply Why are automobiles made with steel,which corrodes easily, instead of aluminum,which takes longer to completely corrode? (8)

7. Thinking Critically Give the word equationfor photosynthesis and the word equation forrespiration. Describe the similarities and dif-ferences between these two reactions. (7)

Wrap-up Topics 7–8 • MHR 165

T O P I C S 7 - 8Wrap-up

chemical reactionreactantsproductsexothermic

endothermicreaction ratecatalyst

enzymeinhibitorscorrosion

rustgalvanizationcombustion

1

3

6

7

8

9

4

2

5

Across1. a type of corrosion3. gives off energy6. a type of catalyst7. after the reaction8. coat with zinc9. slows down processes

Down1. before the reaction2. burning3. deposit using currents4. needs energy5. speeding up, but not involved

ExpertAsk an

U N I TU N I T


Q What does a forensic technician do?

A Forensics means evidence worthy of presenta-tion in court or other judicial proceedings.Our job is to attend crime scenes, identifypotential evidence, photograph and sketch evi-dence, and collect and preserve evidence. Inshort, the Forensic Identification Unit isabout matching physical evidence found at acrime scene to a perpetrator. It is like playinga “who done it” game, but for real. We applyscientific methodology to police work inrecording and collecting of evidence.

Q What kind of evidence do you analyze?

A Evidence can include hair and fibres at the pointof entry; footwear impressions in snow, in sand,or on linoleum floors; blood spatter on clothing,floors, or walls; or latent (hidden or undetected)fingerprint impressions on just about any surfacetype. In recent years our evidence collection hasalso included DNA (deoxyribonucleic acid)analysis. DNA is like a biological-chemical fin-gerprint. Except for identical twins, everyonehas his or her own unique DNA signature. Thisis an exciting addition to police work. Just adrop of blood, a flake of skin, or a single hair isoften enough to solve a crime and identify theperpetrator.

Q What tools do you use to analyze evidence?

A We always use our cameras to show what thescene or material looked like before we didany work to it. Our notebooks are just asimportant as our cameras. We can neverremember all the details of something we sawor did, so we record it all in our notebooks.We use fine silica fibres and camel-hair brush-es to apply powder to items we want to dustfor fingerprints.

Q How do you use chemicals in your job?

A We have a laboratory full of chemicals to helpus develop fingerprints on paper, plastics,cardboard, and other smooth surfaces. Someof the chemicals we use enhance the detectionof the fingerprints. Other chemicals are usedto help locate and identify blood, urine, andother bodily fluids. We also have a speciallight that is used to project a laser poweredultraviolet light. This is called a Luma-Liteand is very useful in detecting bodily fluidsand blood even after someone has tried toclean them up.

ExpertAsk an

When Merle Fuller was a student, he loved to read mystery

novels and watch mystery shows. He liked not knowing who

the villain was and using his deductive reasoning to solve

the mystery. Today he works in a job that he says is just like

living in a mystery novel. Merle is a forensic technician with

the Lethbridge Police Department.

U N I TU N I T

Ask An Expert • MHR 167

Q Have you ever seen a crime scene without evidenceleft by the perpetrator?

A Every perpetrator leaves a mark at a crimescene because every perpetrator has a uniquestyle or method of doing things. Even if theperpetrator wears gloves, he or she has to getinto the room somehow. A perpetrator willlikely leave tool marks, footwear impressions,fibres, and even blood or skin cells. No onecan enter a room without leaving somethingbehind. A forensic technician needs to be per-sistent and dedicated enough to find the evi-dence.

Invisible FormulasInvisible ink has been used for hundreds of yearsto send secret codes, messages, and formulas tofamily members, government officials, and spies.You can use invisible ink to send a secret formulato your classmate. All you need are toothpicks,lemon juice, index cards, and a source of heatsuch as a candle or hot plate.

Dip the toothpick into the lemon juice and use itlike a paintbrush to write one of the chemical for-mulas you have learned in this unit. Allow the cardto dry for a few minutes. The formula and mes-sage will become invisible.

Exchange cards with someone. Light a candle andhold the index card at least 4 cm above the flame.You only want the heat from the candle to reactwith the chemicals on the paper. You do not wantto burn the paper. The hidden formula shouldappear written in brown-black letters.

If you want your message to disappear again,gently dab a cotton ball soaked in householdbleach on the index card. The carbon will disap-pear. Is the disappearance of the carbon anotherchemical reaction or is it a physical reaction? Howcould you find out?

Other invisible inks can be made with a mild solu-tion of baking soda in water, or ammonia in waterand milk. Try these inks and test whether thechemical reaction involving oxidation is as notice-able as the one you have just witnessed withlemon juice. What other juices might work?

Figure 2.67 A forensic technician might test clothing withan indicator that reacts with light. This glowing spotindicates the presence of blood.

Think About ItCorrosion is a common chemical reaction. Everyyear many items made of steel, such as railwaytracks, bridges, and automobiles are slowly eatenaway. Steel can be protected from oxidation if it iscoated with a more active metal such as zinc. Zincloses electrons to oxygen more readily than irondoes, forming a tough protective layer of zincoxide. The coating of zinc and zinc oxide preventsthe formation of rust by keeping oxygen fromreaching the iron.

The amount of corrosion that occurs is depen-dent on factors such as amount of moisture, amountof oxygen, type of metal, and whether a protectivecoating covers the metal. In this investigation youand your team members will study corrosion inAlberta and think of a question about corrosion youwould like to investigate. Formulate your questionbased on information you have studied in this unitand information you may find by researching onthe Internet. (Hint: Use the key words Alberta+cor-rosion+metals when you do your search.)

Your task is to think of a question to investigateabout corrosion. Be sure to have your materials andexperimental steps approved by your teacher beforeyou assemble any materials or begin your investiga-tion. You may use other metals, but consider usingnails, which can be easily purchased at a local hard-ware store. You might investigate the protectionprovided by galvanizing nails. Or you might wantto investigate the factors necessary to cause corro-sion. The diagram of test tubes on this page indi-cates one possible experiment you could perform.


Tough as Nails

Figure 2.68 The bucket on theleft has been galvanized.

cleanironnail

tap water

wetcottonball

1 2 3

anhydrouscalciumchloride

rubberstopper

4

olive oil

5

boiled water

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

MaterialsBrainstorm a list of the materials that will be mostappropriate in answering your question. You mayalso need electronic resources, art materials, orconstruction materials.

Safety Precautions• Do not mix chemicals without your teacher’s

knowledge and approval.

• List additional safety precautions as you design your experiment.

Initiate and Plan With your group, decide on an experimentalquestion to investigate. You might need to dosome further research in order to decide onthe question.

Formulate a hypothesis or a prediction thatwill answer your question. Base your hypothesis on previous knowledge and oninferences that you can make as a result of that knowledge.

Design an experiment to test your hypothesisor prediction. Use words and diagrams toexplain your design. Think about the order inwhich you could carry out the steps in yourprocedure. Decide on the feature you willchange (the manipulated variable) and the feature you will observe changing (theresponding variable). Decide what your control will be. You might find it helpful torefer to the Experimental Design Checklist.

Perform and Record (Test Your Hypothesis)

Set up and perform your experiment. If necessary, carry out second and third trials.Make any modification to your experiment, if necessary.

Gather and record data and observations asyou conduct your experiment. Decide how torecord and present your data in a clear format(table, graph, diagram, etc.).

Analyze and Interpret (Draw Conclusions)

Draw conclusions based on the results of yourexperiment. Discuss your conclusions withyour group.

Did your findings support your hypothesis?Explain.

Write up your findings in a laboratory report.Be sure to include the following:• Introduction• Hypothesis or Prediction• Procedure (step by step), including a

diagram• Data/Observations in the form of words

combined with graphs, tables, etc.• Conclusions

Unit 2 Design Your Own Investigation • MHR 169

Experimental Design Checklist1. Have you clearly stated the purpose of

your experiment, the question you wantto answer?

2. Have you written your best guess (hypothesis) about what you expect theanswer will be?

3. Have you written a step-by-step procedure?

4. Have you obtained all the information youneed from a variety of sources?

5. Did you make a complete list of all the materials you need?

6. Have you identified all of the variables inyour experiment?

7. Identify all sources of error that you canthink of in your design.

8. Did you repeat your experiment severaltimes? How many?


U N I TU N I T

Unit at a Glance• All chemicals should be treated with respect. The

WHMIS safety symbols have been adopted tosafeguard the classroom, home, and workplace.

• All matter is made of atoms and can exist inthree states. Matter can be divided into mixturesand pure substances.

• Physical changes cause a change in state, shape,or size of matter.

• Chemical changes create new substances. • Pure substances can be divided into elements

and compounds. A chemical formula is used todescribe elements and compounds.

• Elements are organized into a periodic tableaccording to similarities in their properties. Manyscientists, including Mendeleev, Dalton, Thomson,Rutherford, and Bohr helped to develop the mod-ern view of the elements, compounds, and atoms.

• The law of conservation of mass and the law ofdefinite composition help explain the behaviour ofelements and compounds in chemical reactions.

• Atoms are composed of small particles includingelectrons, protons, and neutrons. Electrons have atendency to be found in pairs.

• Elements can be divided into metals, non-met-als, and metalloids depending on their physicaland chemical properties.

• Chemical symbols are used to represent ele-ments and compounds. Chemical equations areused to represent chemical reactions.

• Chemical reactions are indicated by the creationof heat, light, the presence of a precipitate orgas, or a change in colour or odour.

• Compounds can be identified as molecular orionic. Compounds are named according to rulesestablished by IUPAC.

• Exothermic reactions produce heat.Endothermic reactions require heat.

• Catalysts speed up chemical reactions. Inhibitorsslow down chemical reactions.

• Some metals corrode when they are exposed to

air and moisture.• Combustion is a highly exothermic combination

of a substance with oxygen.

Understanding Key Concepts1. Draw and label the symbols for the eight main

categories in the WHMIS system.

2. List one physical and one chemical propertyfor each of these elements: carbon, neon, andsilicon.

3. Give four examples of pure substances, threeexamples of solutions, and three examples ofmechanical mixtures that you might encounterduring an average day.

4. What is the difference between a metal and anon-metal? Give three examples of each.Write their chemical formulas in parenthesesafter the names.

5. Here are some answers to questions aboutUnit 2. Make a question for each answer thatcould appear on a test for the unit.(a) conservation of mass(b) endothermic reaction(c) physical properties(d) chemical reaction

6. Describe an investigation in which you couldcontain and compare the quantity of reactantsand products in a chemical reaction.

7. Give two examples of common reactions thatinvolve chemical change. Write chemicalequations for the reactions.

2 Review2 Review

8. Identify four conditions that affect rates ofchemical reactions.

9. Describe the effects of corrosion. What mea-sures can be taken to prevent corrosion?

10. Explain the difference between observationand theory. Give one example of each.

11. How could you distinguish between a physicalreaction and a chemical reaction?

12. Draw and label sketches of the atomic modelsof Dalton, Thomson, and Bohr.

13. Using chemical equations, write the chemicalreactions for the following: photosynthesis,combustion, and corrosion of iron.

14. Which groups are divided by the “staircase”on the periodic table? How do their properties differ?

15. What could Dalton’s atomic theory explainabout matter that the particle model could not?

16. Describe a physical change that is not easilyreversed.

17. Refer to the photograph of solid carbon diox-ide (dry ice) in water on this page. Is the fogcreated an example of a physical or chemicalchange? How do you know?

Developing Skills

18. Refer to the photograph of lightning on thispage. Use a dictionary to define chemilume-nescence. How does this property connectwith information you have learned in thisunit? (Hint: Consider physical and chemicalproperties.)

19. Think of a common substance found at home.Write down three of its physical properties.Describe some chemical tests you could perform to identify its chemical properties.

20. Write the word and chemical equations forthis reaction: sodium chloride is producedfrom the reaction of solid sodium with chlo-rine gas.

21. Using the table, answer the following questions:(a) Which of the substances are gases at 60°C?

At �60°C?(b) Which of the substances are liquids at

60°C? At �60°C?(c) Which of the substances are solids at

60°C? At �60°C?

Unit 2 Review • MHR 171

Substance Boiling point °C Freezing point °Cbromine 58 �7

propane �42 �188

silver 2212 961

mercury 357 �39

radon �62 �71

Problem Solving/Applying22. Classify the following elements as metals, non-

metals, or metalloids:(a) silicon(b) neon(c) lithium(d) hydrogen(e) boron(f) phosphorous

23. Name the compounds and state whether eachis ionic or molecular:(a) CaS(b) NO(c) H2O(d) AlN(e) SO3

(f) CO(g) AgI(f) Fe2O3

(f) CaCl2

24. Baking soda has the formula NaHCO3. Howare the properties of this compound differentfrom the properties of the elements fromwhich it was made?

25. During an experiment, two solid compoundsburn in the presence of oxygen. Can you con-clude that they are the same compound? Whyor why not?

26. Describe an experiment you could perform todetermine if a reaction is exothermic orendothermic.

27. What does the formula C2H6O tell you aboutthe substance it represents? Be specific in youranswer.

Critical Thinking28. How are salt and a diamond similar? How are

they different?

29. If you place a salty cracker in your mouth andstart to chew it slowly, it will begin to tastesweet. Use your knowledge of chemical reac-tions to explain why this happens.

30. Sucrose breaks down slowly in water to formsmaller sugar molecules like glucose. If a smallamount of acid is added to the water, the reac-tion will happen much faster. The acid is notused up in the reaction. Explain the role of theacid in the reaction and give it a chemical name.

31. Propane is often used to cook food on an out-door barbecue. Write a chemical equation forthe reaction taking place when the propane isignited. Write a word equation for what hap-pens to food as it is cooked on the barbecue.

32. List one piece of evidence you would expect tosee indicating a chemical reaction is takingplace in each of the following situations:(a) A candle is burning.(b) Baking soda reacts with vinegar.(c) A glass of milk is left on the kitchen

counter for a week.(d) A bagel is burned in the toaster.

33. Why might it be impossible to chemicallychange copper into gold as the alchemiststried to do?

34. Using a bag of microwave popcorn as anexample, describe an experiment to illustratethe law of conservation of mass.

35. What difficulties would arise if materialswere classified by appearance rather thancomposition?


36. Examine the photograph on this page. Apacemaker is a device inserted in the body tohelp regulate the rhythm of the heart. Thebattery that powers a pacemaker is oftenmade with lithium. Which properties makelithium a good choice for the battery? Whichproperties of lithium could be a source ofproblems for this application?

37. A beaker containing a substance becomescooler when you add another substance to it.What can you infer from this observation?

38. A beaker of coloured water becomes warm asit sits in the sunlight. Has a chemical reactionoccurred? Explain.

39. How has understanding the atom changed theway scientists investigate chemistry?

40. List two elements and two compounds thatcan be dangerous to human health and/or theenvironment. Explain the danger of each, andidentify the WHMIS symbols that should be labelled.

Unit 2 Review • MHR 173

Turn back to page 90 and reread the Focussing questions.For each question make a mind map (web) connecting theinformation you have learned in this unit. What other ques-tions do you have about chemistry?

topic 8 reaction rate

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