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Atoms, Elements,and CompoundsAtoms, Elements,and Compounds

Each of these octopus-like structures has a tinymetal head and“nanowire” arms made ofsilica. Silica is a commonsubstance with usefulcharacteristics. It is, forexample, a major part ofsand and glass. Silicananowires, shown heremagnified about 20 000times, can be used incommunications devices.

U N I T

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http://www.sciencesource2.ca/pgs/searchpage.php?search=130&submit=Go

Unit Task

Every substance has special properties that may makeit useful or hazardous or both. In this unit, you willlearn about the components that make up differentsubstances and give them their unique properties. Inyour Unit Task, you will design and test a toothpasteand investigate the properties of the ingredients thatyou use.

Essential QuestionWhat properties make one substance different fromanother?

Matter has physical and chemical properties.

4.1 Investigating Matter

4.2 Physical and Chemical Properties

The periodic table organizes elements bypatterns in properties and atomic structure.

5.1 Developing the Atomic Theory

5.2 The Elements

5.3 The Periodic Table

Elements combine to form ionic compoundsand molecular compounds.

6.1 How Compounds Form

6.2 Names and Formulas of Common Compounds

6.3 Balancing the Hazards and Benefits of Elementsand Compounds DI

DI

DI

Contents

4

5

6

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We use plastic bags to carry groceries, package food, and contain garbage. When plastic bags are not recycled, they often become litter.

Plastic WorldCount the number of plastic items that you can see around you.People use plastic pens, cutlery, and bags. We use plastic in shoes,computers, cellphones, furniture, and cars. We use plastic to makefood containers and the refrigerators they are stored in. There aremany reasons that plastics are so widely used.

A plastic is a material that can be shaped when soft and thenhardened. This characteristic is very useful. There are manydifferent kinds of plastics. Some plastics are made into sturdystructures and can be used to replace or strengthen human bodyparts, such as a faulty heart valve. Other types are made into thin,flexible sheets, perfect for making bags. Many plastics do notbreak down easily. This characteristic is useful for making long-lasting structures, such as outdoor furniture, or items we useevery day, such as household appliances. Plastic containers andgloves are very useful for safely handling corrosive chemicals.Chemistry helps us explore these and other characteristics ofsubstances.

132 UNIT B Atoms, Elements, and Compounds

Exploring

We would need tomake many changesin our everydaylives if we did nothave plastics.

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133Exploring

The Lifetime of the Plastic BagPlastic bags often end up as litter instead of being recycled. Insome countries, so many plastic bags litter streets that the plasticshopping bag is known as “the national flower” or “the nationalflag.” Plastic bags have clogged storm drains, causing floods. Thebags can also kill marine animals that eat them. For these reasons,and to save resources, many communities around the world haverestricted the use of plastic bags.

A typical plastic shopping bag is made of polyethylene.Polyethylene is relatively inert, which means that it does notreact easily with other chemicals. This makes polyethylene useful,but since it does not easily break down in the environment, caremust be taken to reduce its use and to recycle or dispose of itresponsibly.

The Town of Leaf Rapids, Manitoba, once spent thousands ofdollars each year to clean plastic bags out of the forest. Bagsscattered by the wind would cling to trees and fences near thetown garbage dump. The town wanted a solution, and so LeafRapids became the first community in Canada to ban disposableplastic shopping bags.

B1

Do We Need Plastic Shopping Bags?

When we are finished using a plastic bag, we arefaced with its disposal. Recycling is one option,but this uses energy and resources, possibly morethan making the plastic bag in the first place.

Plastic bags and other polyethylene productsoften end up in landfill — or as litter — and maynot break down for decades.

1. Should disposable plastic shopping bags bemade illegal? Make a table with the headings“Advantages” and “Disadvantages.” Giveyour table a title. Identify at least twoadvantages and disadvantages of this idea.Decide your position, and defend yourstance in a class discussion.

2. At 16 years old, Daniel Burd won theCanada-Wide Science Fair for discoveringthat a certain type of bacteria can degradeover 40 percent of the weight of plastic bagsin less than 3 months. How could thisdiscovery be applied to improve theenvironment?

3. Plastic bags are not only used for shopping.List three other common uses for plasticbags. Can plastic shopping bags be safelyreused for these other purposes? Explain.

Science, Technology, Society, and the EnvironmentSTSE

Sea turtle eating a discarded plasticbag

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4 Matter has physical and chemicalproperties.

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Matter has physical and chemical properties. 135

The same properties of water that cause it to form beadson the surface of a leaf allow water to form a columninside a plant's stem. The column of water stretchesfrom the roots to the top of even the tallest trees.

Skills You Will UseIn this chapter, you will:

• investigate and identify the physical and chemicalproperties of substances

• plan and conduct an inquiry into the properties of commonsubstances

• conduct tests to identify gases

Concepts You Will LearnIn this chapter, you will:

• assess the usefulness and hazards of polyethylene

• use appropriate terms to describe elements andcompounds

• describe the physical and chemical properties of commonelements and compounds

Why It Is ImportantPlastic, diamond, road salt, and table salt are different typesof matter with their own special properties. Understandingthe properties of matter helps us to work safely with differentsubstances and to change them to make useful things.

The Language of Chemistry

Make a “Language of Chemistry” chart for the termsbelow. Your chart should have three columns: Key Term,Before Reading, and During Reading. Under Key Term,write each word on its own row in the chart. Recordwhat you think each term means in the Before Readingcolumn of the chart by either writing a statement ordrawing a diagram. As you read the chapter, make notesfor yourself in the During Reading column to clarify yourideas about each term.

Key Terms

• adhesion • chemical change • chemical property • cohesion • combustibility • mechanical mixture • physical property • pure substance • solution

Before Reading

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The Chemistry of FireworksOn Canada Day, when darkness falls, the skies of towns andcities across the country come alive with colours and sounds.Flares of red, blue, green, and white are joined by cracks andbangs as fireworks displays mark Canada’s national day ofcelebration (Figure 4.1). Fireworks are an ancient technology,first invented in China over 2000 years ago. Today, fireworks canbe seen around the world and creating them is an art form calledpyrotechnics. Pyrotechnics is a branch of chemistry, the scienceconcerned with understanding and changing matter.

The spectacular sights, sounds, and smells of fireworks comefrom the fusion of science and art. The designers of fireworksknow that some substances burn with brilliant colours whenheated (Figure 4.2). Aluminum metal is used in the kitchen ascooking foil. However, when aluminum is heated by an explosion,the metal burns with a bright white flame. To use aluminum infireworks, it is first made into a powder so that it will burnquickly and spread out easily. The types of fireworks that light upthe night sky or leave a thick glowing trail of light often containaluminum.


Here is a summary of what youwill learn in this section:

• Matter has mass and occupiesvolume.

• Matter is composed ofparticles. The arrangement andmovement of the particlesdetermines whether asubstance is solid, liquid, orgas.

• Matter can be classified as apure substance or a mixture.

• Mixtures can be furtherclassified as mechanicalmixtures, suspensions, andsolutions.

Investigating Matter

Figure 4.1 Fireworks displays combine art and chemistry.

4.1

Figure 4.2 Fireworks are lit with aflame.

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137Matter has physical and chemical properties.

B2 Quick Lab

Observing Changes in Matter

When substances are mixed, they may change instate or they may change into different substanceswith different characteristics. Watch for changes incolour, volume, and state (solid, liquid, or gas) as youcomplete this activity.

PurposeTo observe changes in matter

Procedure

1. Measure about 30 mL of bromothymol blueindicator solution into a small beaker.

2. Hold open a resealable plastic bag. Place onescoop of sodium hydrogen carbonate powder inone corner of the bag. Place one scoop of calcium chloride powder in the other corner of the bag.

3. Pour about 30 mL of bromothymol blue indicatorsolution into the bag. Squeeze out the air, andquickly seal the bag.

4. Mix the contents by squeezing the bag for about20 seconds. Use your hands to detect anytemperature changes.

5. Observe as many kinds of changes to the matterin the bag as you can.

6. Clean up your work area. Follow your teacher’sinstructions to safely dispose of all materialsused. Wash your hands thoroughly.

Questions

7. Describe what you observed when you:

(a) added indicator solution to sodium hydrogen carbonate

(b) added indicator solution to calcium chloride

(c) mixed the indicator solution and both powders

8. Were there any changes to the substances in thisactivity? How do you know? What evidence didyou observe?

• medium graduated cylinder

• small beaker

• bromothymol blue indicator solution

• water

• resealable plastic bag

• 2 scoopulas

• sodium hydrogen carbonate powder(baking soda)

• calcium chloride powder

Materials & Equipment

Many substances change colour when heated. The green coloursin fireworks usually come from heated copper substances, while thebright oranges are based on another substance called sodium, whichis present in ordinary table salt. The crack and bang of fireworks areproduced when certain substances heat up and rapidly expand. Therapid expansion makes the sound. The explosions are often sopowerful that they can be felt as well as heard.

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Matter Has Many FormsMatter is anything that has mass and volume. Mass is a measureof the quantity of matter in an object. For example, a brick hasmore mass than an equal-sized volume of Styrofoam®. Mass isoften measured in kilograms (kg) or in grams (g). Volume is ameasure of how big an object is or how much space a fluid takesup. For example, a volleyball is larger than a baseball. Volume isoften measured in litres (L) or in millilitres (mL). All matter hassome volume, even if that volume is very small.

Matter can be solid, liquid, or gas or a combination of thesestates. For example, foam is a mixture of a liquid and a gas, or asolid and a gas. Bubbles in a foamy bubble bath are liquid films ofsoap with air trapped inside them. Styrofoam® is a solid plasticcontaining trapped air. Lightweight aluminum foam can be madeby trapping gas inside melted aluminum and then letting themetal harden (Figure 4.3).

Changes of StateSolids, liquids, and gases are called states of matter. Specific termsare used to describe changes of state of a substance (Figure 4.4). Achange from a solid to a liquid is melting. A change from a liquidto a gas is evaporation (also known as vaporization). A changefrom a gas to a liquid is condensation and from a liquid to a solidis freezing. A solid can also change directly into a gas throughsublimation. The opposite change is deposition, in which a gaschanges directly into a solid.


Figure 4.3A piece ofaluminumfoam

solid

sublimation

liquid

deposition

melting

freezing

evaporation

condensation

gas

Figure 4.4 Changes in states of matter

Suggested Activity •B4 Quick Lab on page 146

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The temperature at which a solid turns into a liquid is calledthe melting point. For example, the melting point of water is0°C. The reverse process, freezing, occurs at the freezing point.The melting point and the freezing point are always the sametemperature. Similarly, the temperature at which a liquid turns toa gas is called the boiling point. The boiling point is the sametemperature as the condensing point, the temperature at which agas changes into a liquid.

The Particle Theory of MatterThe particle theory of matter is a way to describe the structureof matter and its behaviour (Figure 4.5). Matter can be broken intosmaller and smaller pieces. Is there a limit to how many times apiece of graphite from a pencil can be divided and still be graphite?The answer is yes. The smallest possible pieces of graphite areparticles. The particle theory of matter explains how this works.

• All matter is composed of very tiny objects calledparticles. These particles are too small to be seen, evenwith a powerful light microscope.

• All particles have spaces between them. The distancesbetween the particles change for different states of matter.For example, particles in a liquid have more space betweenthem than the particles in a solid of the same substance, butparticles in a liquid have less space between them thanparticles in a gas.

• Particles present in matter are always in motion. Theymay be vibrating back and forth, as in a solid, or moving inall directions, as in a gas. In a liquid, particles stay closetogether but can slide past one another.

• The particles in a substance attract each other. Theamount of attraction is different for different kinds ofparticles. In iron, which is a very hard solid at roomtemperature, the particles strongly attract each other. Inwater, which is a liquid at room temperature, the particlesof water can slide past each other because the attractionsbetween them are not very strong.

For a given substance such as water, the state it is in is relatedto its temperature.


solid

liquid

gas

strong force close together

very weak forcevery far apart

weaker forcefarther apart

Figure 4.5 Particles are arrangeddifferently in a solid, a liquid, or a gas.

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Particles and HeatIn ice, the particles of water vibrate in place but cannot movearound. They attract each other strongly, forming a solid. As heatis added, the particles of water vibrate more quickly, whichweakens the attraction between them, allowing them to slide pasteach other (Figure 4.6). This allows water to flow as a liquid.When enough heat is added, the particles of water break free fromeach other and separate, forming a gas.


Learning Checkpoint

1. What are two features that all forms of matter have?

2. Use the particle theory of matter to explain what makes a liquid differentfrom a solid of the same substance.

3. Compare the amount of space between particles of a gas with that of aliquid of the same substance.

4. What is the effect of adding heat to the particles in a sample of matter?

5. What is the difference between the melting of water and the melting pointof water?

Figure 4.6 (a) When enough heat is added to ice, (b) the particles of water begin toslide past each other. (c) Eventually, the particles spread apart, forming a gas.

(a)

(c)

(b)

During Reading

Examples Help Give a Word Meaning

Authors use examples to helpreaders really see the meaningof a word in their minds. If youcan picture the example, youcan usually understand theconcept or idea. Watch forexamples as you read to helpyou understand new terms.

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Classifying MatterAll matter is made up of different types or combinations ofparticles. For example, gold and iron are both metals, but theyhave very different characteristics. Pure gold is yellow and is sosoft that a fingernail can put a mark on it, whereas iron is silver-coloured and much too hard to scratch with a fingernail. Thesetwo metals have different characteristics because the particlesthat make up each are different. That is, all particles of gold areidentical, and all particles of iron are identical, but particles ofgold are different from particles of iron.

Different types and combinations of particles give every typeof matter particular characteristics, or properties. A property is acharacteristic that describes a substance.Substances may be classified as puresubstances or mixtures, depending on howtheir particles are arranged.

Pure SubstancesA pure substance is made up of only onekind of matter and has a unique set ofproperties, such as colour, hardness, boilingpoint, and melting point. A pure substance iseither an element or a compound. Forexample, gold is an element and sugar is acompound (Figures 4.7 and 4.8).

• An element is a substance that cannotbe broken down into any simplersubstance by chemical means. Later inthis unit, you will learn how elementsare organized into a periodic tableaccording to their properties. Eachelement has its own name and symbol.For example, hydrogen’s symbol is H.

• A compound is a pure substance that ismade from two or more elements thatare combined together chemically. Forexample, water (H2O) is a compoundcontaining the elements hydrogen andoxygen.


Figure 4.7 An ancient gold mask from Peru in South America. Gold isan element and a pure substance.

Figure 4.8 Sugar is a compound and a pure substance. All sugarparticles are like all other sugar particles. It is a compoundbecause sugar particles are made of more than one element.

Suggested Activity •B3 Inquiry Activity on page 144

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Figure 4.10 A salad vinaigrette is a mixture of oil, vinegar, andspices. When shaken, they form a suspension. After a while, thecomponents will separate. This is why salad dressings areusually shaken before using.

MixturesA mixture is a combination of pure substances. However, thesubstances in a mixture do not combine chemically as happenswhen a compound forms. Each substance remains in its original,pure form, although each is not always easy to see distinctly oncethe mixture is made. There are three main types of mixtures.

• In a mechanical mixture, the different substances thatmake up the mixture are visible (Figure 4.9). Soil is anexample of a mechanical mixture. So is a mixture of salt andpepper. A mixture in which the different parts are visible iscalled heterogeneous. The prefix “hetero-” means different.

• A suspension is a cloudy mixture in which tiny particles ofone substance are held within another (Figure 4.10).Tomato juice is an example of a suspension. These particlescan be separated out when the mixture is poured throughfilter paper. A suspension is also a heterogeneous mixture.

• In a solution, the different substances that make it up arenot individually visible (Figure 4.11). One substance isdissolved in another, creating a homogeneous mixture. Theprefix “homo-” means same, and all parts of a homogeneousmixture look the same. Examples of solutions are sugardissolved in hot coffee, and acetic acid dissolved in water tomake vinegar.


Figure 4.9 A chocolate chip cookieis a mechanical mixture. Differentparts of the mixture are visible.

Figure 4.11 Tea is a solution of water and the extract of tealeaves that are dissolved in the water. A solution ishomogeneous. Every part of the tea looks like every other part.

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A Summary of Matter ClassificationAll matter can be classified as either a pure substance or amixture. Mixtures are either heterogeneous or homogeneous.This is summarized in Figure 4.12.


matter

heterogeneousmixtures

homogeneousmixtures

solutionssuspensionsmechanical

mixtures

mixtures

elements

pure substances

compounds

Figure 4.12 The classification of matter

Learning Checkpoint

1. How is a compound different from an element? Give an example of each.

2. What is the difference between a mixture and a pure substance?

3. How is a suspension different from a solution?

4. Classify each of the following as either a pure substance or a mixture.

(a) Pop is composed of water, sugar, and carbon dioxide.

(b) Carbon dioxide is composed of carbon and oxygen chemicallycombined.

(c) Sand is composed of white grains and black grains.

(d) The graphite at the centre of a pencil is composed of carbon.

Just like salt and other solidcrystals, liquid crystals are puresubstances with an orderedarrangement of matter. However,the fluidity of liquid crystals givesthem some unusual properties.For example, some liquid crystalschange colour with temperaturechanges. Find out about otherproperties of liquid crystals byvisiting ScienceSource.

Take It Further

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B3 Inquiry Activity

Changes to matter can result in the formation ofgases. There are many different kinds of gas, and wecan use their properties to help identify them. Threecommon gases are hydrogen, oxygen, and carbondioxide.

• Oxygen gas will cause a glowing splint toreignite (catch fire).

• Carbon dioxide gas will put out a flame.

• Hydrogen gas will make a “pop” sound in thepresence of a flaming splint.

PurposeTo use gas tests to identify oxygen gas, carbon dioxidegas, and hydrogen gas

ProcedurePart 1 — Preparation of Oxygen

1. Using a medicine dropper, add 1 mL (about 20 drops) of hydrogen peroxide solution to aclean test tube.

2. Add two drops of dish soap.

3. Using a scoopula, add a small amount (less thanthe size of a pea) of potassium iodide powder tothe test tube.

4. Use matches to light a wooden splint.

5. Blow out the flame to make a glowing splint. Insertthe glowing splint into the mouth of the test tube.Observe and record what happens to the splint.

6. Clean up as directed by your teacher.

Part 2 — Preparation of Carbon Dioxide

7. Using a medicine dropper, add 1 mL (about 20 drops) of acetic acid to the second clean testtube.

Identifying Gases

SKILLS YOU WILL USE� Conducting inquiries safely� Processing and synthesizing

data

CAUTION: Hydrogen peroxide may sting your skin.Potassium iodide will stain skin and clothing. Keep yourhair tied back when working near open flames.

• 3 medicine droppers

• 3 medium test tubes

• test-tube rack

• 3% hydrogen peroxide solution

• dish soap

• scoopula

• potassium iodide powder

• matches

• wooden splints

• 0.1 M acetic acid solution

• sodium hydrogen carbonate powder

• 2 M hydrochloric acid solution

• forceps

• mossy zinc chunks

• 1 large test tube

• test-tube holder


Skills Reference 1

Figure 4.13 A glowing splint will reignite in the presence of oxygen.

Key ActivityDI

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B3 Inquiry Activity (continued)

8. Using a clean scoopula, add a small amount (lessthan the size of a pea) of sodium hydrogencarbonate powder to the test tube.

9. Use matches to light a wooden splint.

10. Insert the flaming splint into the test tube.Observe and record what happens to the splint.

11. Clean up as directed by your teacher.

Part 3 — Preparation of Hydrogen

12. Using a medicine dropper, add about 2 mL ofhydrochloric acid to the third clean test tube.

13. Use forceps to add a small piece of mossy zinc tothe third test tube. Use a test tube holder toplace a large test tube upside down and over thesmaller test tube in order to trap any gas.

14. Keep holding the large test tube upside down asyou lift it off of the small test tube. Use matchesto light a wooden splint.

15. Insert the flaming splint into the large test tube.Observe and record what happens to the splint.


Analyzing and Interpreting

17. Describe what happens in a positive test foroxygen gas.

18. Describe what happens in a positive test forcarbon dioxide gas.

19. Describe what happens in a positive test forhydrogen gas.

Skill Practice

20. Write a procedure for distinguishing betweenoxygen gas and carbon dioxide gas.

Forming Conclusions

21. Explain why the three parts of this activity can beused to distinguish among oxygen, hydrogen, andcarbon dioxide gas but not to determine whetheran unknown gas is one of these three.

Figure 4.14 A flaming splint will be extinguishedin the presence of carbon dioxide.

Figure 4.15 Trapping hydrogen gas

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B4 Quick Lab

You can manipulate matter to change its properties.In this activity, you will mix together different liquidsand a solid to produce a completely differentsubstance: a foam.

PurposeTo produce a foam and observe its characteristics

Procedure

1. Pour about 30 mL of corn syrup into a beaker.Stir in three drops of one food colouring. Use ateaspoon to sprinkle a heaping spoonful (about20 g) of sodium hydrogen carbonate powder onthe corn syrup.

2. Pour 30 mL of water into the graduated cylinder.Tip the beaker slightly, and carefully pour thewater in down one side. Add 30 mL of vegetableoil to the beaker in the same way.

3. Into a separate beaker, pour 20 mL of vinegar.Add three drops of the other food colouring.

4. Fill the medicine dropper with coloured vinegarfrom the second beaker.

5. Position the tip of the medicine dropper at thevery bottom of the first beaker, then squeeze thebulb in order to release all the vinegar. Recordyour observations.


Questions

7. Write a statement to describe your observationsin step 4.

8. Write a statement to describe your observationsin step 5.

9. What types of changes did you observe?

10. Describe a characteristic of foam that youobserved.

11. Describe the state or states of matter of the foamproduced in step 5.

Foam in a Cup

Figure 4.16 Adding coloured vinegar to the first beaker

• corn syrup

• two 250-mL beakers

• 2 colours of food colouring

• stirring rod

• teaspoon

• sodium hydrogen carbonate powder

• water

• 50-mL graduated cylinder

• vegetable oil

• white vinegar

• medicine dropper


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Key Concept Review1. Water can exist as ice, liquid water, or gas.

In each of the following processes, is heatadded or removed in order to change thestate of water?

(a) evaporation

(b) condensation

(c) freezing

(d) melting

2. According to the particle theory of matter,gases contain particles that are far apart. Dothe particles in a solid have spaces betweenthem? Are the particles moving? Explain.

3. How could you speed up the particles thatmake up the silver in a table fork? Howcould you slow down the particles?

4. How is a mechanical mixture different froma solution?

5. The melting point of aluminum metal is660°C. Is its freezing point slightly lessthan, equal to, or slightly more than 660°C?

Connect Your Understanding6. Tin is a metal with a melting point of

232°C and a boiling point of 2602°C. Whatis its state of matter at each of the followingtemperatures?

(a) 0°C

(b) 1000°C

(c) 2000°C

(d) 4000°C

7. For each of the four statements in theparticle theory of matter, choose one wordthat best sums up that statement’s meaning.Explain your four word choices.

8. Is a compound, such as water, a puresubstance or a mixture? Explain.

9. Identify each of the following as aheterogeneous mixture, a homogeneousmixture, or a pure substance.

(a)

(b)

10. If you put olive oil in the fridge, the oilbecomes solid. Explain what has happenedusing the particle theory of matter.

11. Can a sample of matter exist in two states atone time? Use an example to explain youranswer.

12. Do all substances have the same meltingpoint and boiling point as water? How doyou know?

Reflection13. The particles in matter are too small to see

either with the unaided eye or with a stronglight microscope. Does this fact have anyinfluence on whether you accept thestatements in particle theory or not?Explain why or why not.

14. What are three things about forms of matterthat you learned about in this section?

For more questions, go to ScienceSource.


4.1 CHECK and REFLECT

Question 9

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The Chemistry of a CampfireA fire can be fascinating to watch (Figure 4.17). Although all theflames look similar, each particular spark and flicker is unique —never to be repeated in exactly the same way. With investigation,however, some patterns become clear. Chemistry reveals that allforms of burning are variations on a theme. Every fire needs thesame three components: fuel, oxygen gas, and heat.

In a campfire, the fuel is wood, a complex natural materialthat is rich in carbon. Carbon reacts with oxygen in the air butonly if the air can reach the carbon in the wood. This is why thefirst step in building a campfire is usually to split a log into tinysplinters, called kindling. By chopping a thick log into kindling,much more carbon in the wood is exposed to the air. Oxygen gashas easy access to the carbon at the surface of the wood and socan react with it.

The components of a fire must be in just the right balance.When lighting a fire, extra oxygen is sometimes needed. This iswhy gentle blowing on the first embers of the fire can help. Thereis enough oxygen in the breath to provide the extra boost. It isimportant not to blow the heat of the first sparks away from thefuel, however, as this will blow out the fire. Because combustionreleases heat, there is no need to keep relighting the flame.


Here is a summary of what youwill learn in this section:

• Physical properties describethe characteristics of asubstance that can beobserved or measured.

• Chemical properties describethe reactivity of a substanceand ways in which it forms newsubstances.

• Physical properties includehardness, conductivity, colour,density, melting point,solubility, and viscosity.

• Chemical properties includecombustibility and reactionwith water or acid.

Physical and Chemical Properties

Figure 4.17 A fire produces many changes in matter.

4.2

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During Reading

Understanding Vocabulary

Authors often provide additionalinformation — called an“elaboration” — to help youunderstand a new term or word.As you find new terms orexpressions, look not just for adefinition but also for addedinformation that clarifies the term.

Changes in PropertiesFires produce new substances. One of these is invisible carbondioxide gas. It is formed when oxygen from the air and carbon inthe wood chemically combine. Where does all the wood go whileit is burning? Most of the solid matter in a wood log changes intoa gas and simply blows away. What is left is ash. Ash is a mixtureof carbon compounds that did not have a chance to burn beforethe fire went out and other substances that simply do not burn. Ifleft to burn for long enough, a fire can become smothered in itsown ashes.


B5 Quick Lab

Observing a Physical Change

Soda pop contains carbon dioxide. In the air, carbondioxide exists as a gas. However, when carbondioxide is dissolved in water, this is not the case. Theparticles of water and carbon dioxide are attracted toeach other, so they intermix, forming a solution.Disrupting these attractions produces a change thatyou will observe.

When a substance undergoes a physical change,such as melting, its appearance or state may changebut its composition stays the same. For example,melted chocolate ice cream has the samecomposition as frozen chocolate ice cream. Incontrast, a chemical change results in the formationof a new substance or substances.

PurposeTo investigate a change in matter

Procedure

1. Fill the two glasses about full with soda pop.

2. Into one glass, drop a piece of the mint candy.Observe what happens in both glasses, andrecord your observations.

Questions

3. Adding candy to the soda pop caused a mainlyphysical change that disrupted the attractionbetween particles of liquid. How did yourecognize this physical change?

4. Can you tell whether the composition of thecandy changed after it was added to the sodapop? Why or why not?

5. Consider the change that took place. Suggest onereason that you would describe it as a physicalchange. Suggest one reason that you might alsodescribe it as a chemical change.

6. In the procedure, you were instructed to fill twoglasses with soda pop in step 1 but to add candyto only one glass. What is the reason for this?

7. Suggest ways to modify the procedure to producean interesting effect or display involving thechange in properties. Check with your teacherbefore trying it out.

• 2 glasses

• soda pop

• chewy mint candy


CAUTION: Do not eat or drink anything in the lab, includingthe soda pop and candy.

23

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Figure 4.18 Water sticks to itself,forming droplets (cohesion), and tothe spider web (adhesion).

Physical Properties of WaterAll life on Earth depends on water. Our bodies are about 70 percentwater. Some plants are 95 percent water. A characteristic of water isthat it sticks to itself, a property that is known as cohesion. Due tocohesion, water forms beads on non-absorbent surfaces, such asglass. Water also sticks to other substances, a property known asadhesion (Figure 4.18). Adhesion allows you to mop up water witha towel.

A physical property describes a characteristic of a substancethat can be observed or measured. One example of a physical

property is the melting point of asubstance. Water has manyinteresting physical properties thatmake it very useful to organisms.For example, adhesion and cohesionhelp move water up through thestems of plants, including tall trees.Its ability to be a liquid at roomtemperature is another.

Most materials shrink when theyfreeze. Water does not. Due to specialinteractions between water particlesduring freezing, water actuallyexpands. This makes ice less densethan liquid water. As a result, ice

floats on water. Why is this important? In winter, the ice on a bodyof water shelters the fish below. Floating ice can also make a usefultemporary roadway or platform for ice fishing (Figure 4.19).However, the same properties that make water useful can also causeproblems. As ice forms, it widens cracks in roads. In addition, snowand ice on the roofs of houses can cause damage when it melts andrefreezes. Not only is the ice heavy, it can block gutters anddownspouts that are meant to keep water flowing off the roof andaway from the sides of the building.

Observing Physical PropertiesFigure 4.20 shows a dull, red, clouded piece of beach glass. Threephysical properties of the glass include its lustre (shiny or dull), itscolour, and its transparency (how see-through it is). Other physicalproperties can be observed using special equipment. For example, youcould measure the mass and the volume of the glass to determine itsdensity. Table 4.1 lists a number of other physical properties.


Figure 4.19 In winter, fish areprotected from freezing temperaturesby the ice at the surface of the water.People can use this same ice as aplatform when fishing.

Figure 4.20 The pieces of beachglass show a variety of physicalproperties.

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Table 4.1 Physical Properties of Matter


Property Description Examples What It Looks Like

Colour and lustre The light a substancereflects gives it colour andlustre (shine).

The names for somesubstances, such as gold,are also the names ofcolours. Gold has lustre;concrete is dull.

Conductivity Conductivity is the abilityof a substance to conductelectricity or heat. Asubstance that conductselectricity or heat is calleda conductor. A substancewith little or noconductivity is an insulator.

Most metals are goodconductors. Copper is a verygood conductor of electricityand so is used to makeelectric wires. Styrofoam®and glass are insulators.

Density Density is the amount ofmass in a given volume ofa substance.

The density of pure water is1 g/mL. The density of goldis 19 g/mL. Water is denserthan oil, but gold is denserthan water.

Ductility Any solid that can bestretched into a long wireis said to be ductile.

Copper is a commonexample of a ductilematerial.

Hardness Hardness is a substance’sability to resist beingscratched. Hardness isusually measured on theMohs hardness scale from1 to 10.

The mineral talc is thesoftest substance on theMohs hardness scale (1).Emerald is quite hard (7.5).Diamond is the hardest(10).

Malleability A substance that can bepounded or rolled intosheets is said to bemalleable.

Aluminum foil is an exampleof a malleable substance.Metals such as gold and tinare also malleable.

Viscosity Viscosity is the resistanceof a fluid to flow.

Syrup has a high viscositycompared to water.

Gold andsilver coins

Electric circuit withwires to conductelectricity

Fluids and solids withdifferent densities

Copper wire

An emeraldgemstone

Aluminum foil

Pancake syrup

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Observing Chemical PropertiesA chemical property describes the ability of a substance to changeinto a new substance or substances. Chemical properties includehow a substance interacts with other substances, such as acids, orhow it reacts to heat or light. A chemical change always results inthe formation of a new substance or substances. For example, whenzinc metal and hydrochloric acid are mixed, they undergo achemical change that produces two new substances: hydrogen gasand a compound called zinc chloride. A chemical reaction is aprocess in which a chemical change occurs.

Chemical properties can be observed only when a chemicalchange occurs. If you mix baking soda and vinegar, you willproduce a chemical change that involves the formation of gasbubbles. In general, evidence of chemical change can include agreat variety of changes, including colour, odour, temperature, theproduction of light, the formation of a new solid inside a liquid,or the production of a new gas (Figures 4.21 and 4.22). Table 4.2lists various chemical properties.


Figure 4.22 Chemical changes made this banana ripe — and then rotten.

Figure 4.21 Fireflies contain a chemical called luciferin. When luciferin reacts with oxygen,light is emitted.

Suggested Activities •B7 Inquiry Activity on page 156B8 Inquiry Activity on page 158B9 Design a Lab on page 160

Chemical Properties

Absorbs heat during reaction

Combustible

Forms gas when heated

Reacts with acid

Reacts with water

Emits heat during reaction

Emits light during reaction

Forms a precipitate (solid) in asolution

Table 4.2 Examples ofChemical Properties

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water

chemicals that willreact with water

Heat and Chemical ChangeApplying heat to a substance can result in chemical changes. Forexample, when baking powder is heated, it undergoes a chemicalchange that results in the production of carbon dioxide gas. Thisis very useful in cooking. It is this chemical reaction of bakingpowder in some baked foods that produces the gas needed to liftthe cake and make it light and fluffy (Figure 4.23). If you forget toadd baking powder to a cake batter, the cake will be flat and dense.

Heating causes many different kinds of substances to react.Burning is another example of this kind of chemical change.Paper is combustible and so will simply burst into flame whenraised above a certain temperature. Combustibility is theability of a substance to react quickly with oxygen to produceheat and light.

When some substances are mixed, their reaction absorbs heat.A chemical cold pack, for example, depends on a reaction thatabsorbs heat (Figure 4.24). Typically, a chemical cold pack isfilled with water but also has an inner bag or tube full ofchemicals. The inner compartment keeps its contents separatedfrom the water until it istime to use the coldpack. When the innerbag is popped open, thechemicals within mixwith the water in thecold pack. The reactionremoves heat from thesurroundings, and so thepack feels cold to thetouch.


Figure 4.23 When baking powder ina cake batter is heated, it producesa new substance: a gas.

Learning Checkpoint

1. What is a physical property?

2. List three physical properties of water.

3. What is a chemical property?

4. List three examples of chemical properties.

5. How does a physical change differ from a chemical change?

Figure 4.24 A chemical cold packhas an inner compartmentcontaining reactive chemicals and an outer compartmentcontaining water.

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Controlling Changes in Matter to MeetHuman NeedsIn our everyday lives, there are many examples of howunderstanding and controlling changes in matter help us meet ourbasic needs. Consider the freeze-dried foods business. Freeze-drying is a way to preserve foods so that they can be eaten monthsand sometimes years later. As well, freeze-drying makes foods easyto prepare: all you have to do is add hot water (Figure 4.25).

In the freeze-drying process, the food is first frozen to convertthe water content in the food to ice. The frozen food is then put ina pressure chamber, and the pressure is reduced until the icesublimes (changes from a solid to a gas). The result is that about98 percent of the water in the original food item is removed. Thisleaves a food that is about 10 percent its original mass and that,once packaged, does not need to be refrigerated. Freeze-drying isalso used by biologists to study tissue samples and by restorationexperts to rescue important documents that are water damaged.

During hot, dry weather, hikers are often restricted frommaking campfires. However, a fire-free heating pouch has beendeveloped. The freeze-dried food is placed in the heating pouch.The pouch contains the elements magnesium and iron, as well assalt, which is a compound. When water is added to thesechemicals, the resulting chemical change releases enough heat towarm the freeze-dried contents.


Figure 4.25 Freeze-drying removesthe water from food, which preservesthe food until it is time to eat.

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Adding cornstarch to plastic is one way to make the plasticbiodegradable. Find out aboutother “green” products by visitingScienceSource.

Take It FurtherFrom Corn to Biodegradable Plastic WrapBeing able to change materials from one form to another allowsus to make products that are not only useful but which alsosupport a sustainable environment. For example, chemicals madefrom corn can be used to make juice bottles, remove paint or nailpolish, and fuel some cars. Corn is put through a chemical changecalled fermentation. Once this chemical process is complete, thenew substances are recovered, purified, and made into solvents,biodegradable plastics, and automobile fuel.

Solvents are substances that dissolveother substances. Solvents are useful formaking inks and nail polish and forremoving paint. Corn-based solvents are notas harmful to the environment as some othertypes of solvents (Figure 4.26). An advantageof corn-based biodegradable plastics is thatthey can be broken down by bacteria.However, making and using corn-basedproducts also has its drawbacks. Peoplesometimes cut down rainforests to make wayfor cornfields. Corn that would otherwise beused for food is sometimes diverted to makedisposable products.


B6

Polyethylene Plastic

Polyethylene plastic is flexible, heat resistant, andstrong. Children play with polyethylene toys,athletes drink from polyethylene bottles, andpolice officers wear polyethylene vests. Unlikesome other types of plastic, polyethylene isconsidered safe to use in food containers.

What happens to polyethylene products whenwe no longer need them? If they cannot be re-used, another option is to recycle them. Sometypes of polyethylene break down more easilywhen exposed to sunlight. These types of plasticsare considered photodegradable. This processreleases tiny pieces of polyethylene.

1. Make a list of items you used today that aremade from polyethylene. Identify whichitems you could live without and which arenecessities.

2. Describe two ways you could help decreasethe amount of polyethylene that goes intolandfills.

3. What are some possible benefits of usingphotodegradable polyethylene to makedisposable food containers or shoppingbags? What are some possible problemswith this type of plastic?

Science, Technology, Society, and the EnvironmentSTSE

Figure 4.26 The inks used here contain solvents made from corn.

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B7 Inquiry Activity

QuestionHow can you identify a substance from its properties?

Procedure

1. In your notebook, make an observation table likethe one below.

2. Read the labels of the six known whitesubstances, and note any hazard symbols orcautions.

Part 1 — Appearance

3. Place the spot plate on a piece of paper. Label thetop of the spot plate with the tests you will conduct.

4. Label the left of the spot plate with the identity oftwo or more of the six known white substances.Using a clean scoopula each time, deposit asample of each substance in a separate well inthe first column of the spot plate.

Using Properties to Identify Pure Substances

SKILLS YOU WILL USE� Observing and recording

observations� Using appropriate formats to

communicate results

• cornstarch

• magnesium sulphatepowder

• sodium chloridepowder

• sodium hydrogencarbonate powder

• sodium nitratepowder

• sodium thiosulphatepowder

• spot plate

• blank sheet of paper

• grease pencil

• scoopulas

• magnifying lens

• medicine droppers

• water

• 0.5 Mhydrochloricacid

• 5% iodine solution

• unknown substances


Skills References 1, 2, 6

Substance Appearance Crystal Shape Water Acid Iodine

Cornstarch

Magnesium sulphate

Sodium chloride

Sodium hydrogencarbonate

Sodium nitrate

Sodium thiosulphate

Unknown # ___

Table 4.3 Pure Substances Observation Table

CAUTION: Iodine will stain your skin and clothing.

Figure 4.27 Placing substances in the spot plate

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5. Closely observe each white substance. In yourtable, record as many observations as you canabout the appearance of each substance.

Part 2 — Shape

6. Use the magnifying lens to observe the crystalshape of each white substance. Record the crystalshape of each substance as “regular” or“irregular.”

Part 3 — Water

7. Use a clean scoopula to place a bit of the firstsubstance into three more wells in the same row.Do the same for the second substance.

8. Using a medicine dropper, add a few drops ofwater to the second well of the second and thirdrows. Record your observations.

Part 4 — Acid

9. Using a clean medicine dropper, add a few dropsof hydrochloric acid to the third well of the secondand third rows. Record your observations.

Part 5 — Iodine

10. Using a clean medicine dropper, add a few dropsof iodine to the fourth well of the first and secondrows. Record your observations.

11. Clean out the spot plate as directed by yourteacher.

12. Repeat steps 3–11 for the remaining whitesubstances.

Part 6 — Unknown Substance

13. Repeat steps 3–11 for an unknown substanceprovided by your teacher. Be sure to record theunknown substance number in the table.



15. For each white substance, there is one uniqueproperty that distinguishes it from the others.Identify this property for each white substance.

16. Which results from this inquiry were not what youexpected? Explain.

17. How can the properties of the six whitesubstances be used to identify the unknownsubstance?

18. What is the identity of the unknown substance?Explain how your observations support yourconclusion.

Skill Practice

19. Identify the chemical and physical properties youobserved in this activity.

Forming Conclusions

20. Write concluding statements to describe thechemical and physical properties of eachsubstance that you examined.

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B8 Inquiry Activity

You can use a chemical reaction to change onesubstance into another substance that has differentphysical and chemical properties. You can also useheat to change the properties of substances.

QuestionWhat are some characteristics of physical changesand chemical changes?

Procedure1. Copy the following observation table into your

notebook. Be sure to leave a row for each test.

Test 1 — Sodium carbonate andhydrochloric acid

2. Using a scoopula, add a small amount (the sizeof a pea) of sodium carbonate powder to thebeaker. In your observation table, describe theappearance of the sodium carbonate powder.

3. Using a clean medicine dropper, obtain a fewdrops of hydrochloric acid. Observe thehydrochloric acid, and record what you see inyour observation table.

4. Write a statement about the kinds of evidence forphysical or chemical change that you will look forwhen you add the hydrochloric acid to the sodium carbonate.

5. Add five to eight drops of hydrochloric acid to thesodium carbonate. Record your observations.

Test 2 — Sugar and heat

6. Obtain an aluminum muffin tin. Use a cleanscoopula to put a small amount of sugar (the sizeof a pea) in the centre of the aluminum muffintin. Record your observations of the sugar.

7. Suggest possible ways that the sugar mightchange with heating.

8. Place the candle securely in a candle holder,then light the candle.

9. Using tongs or a wooden clothespin, hold thealuminum muffin tin over the candle’s flame.Slowly move the muffin tin back and forth overthe flame to heat the sugar. Record yourobservations.

10. Place the aluminum muffin tin in a safe place tocool.

Investigating Physical and Chemical Changes

SKILLS YOU WILL USE■ Observing and recording

observations■ Justifying conclusions

CAUTION: Copper(II) sulphate is poisonous and canstain your clothes and skin. Keep your hair tied backwhen working near open flames.

Skills References 1, 2

• scoopulas

• sodium carbonatepowder

• 250-mL beaker

• medicine dropper

• 0.5 M hydrochloric acid

• aluminum muffin tin

• white table sugar

• candle

• candle holder

• matches

• tongs or woodenclothespin

• 3 test tubes

• 0.5 M solution ofsodium carbonate

• 0.5 M solution ofcopper(II) sulphate

• two 5-mL measuringspoons

• test-tube rack

• copper(II) sulphate (solid)

• water

• stirring rod


Observations

Test Before Change During Change After Change

Sodium carbonate andhydrochloric acid

Table 4.4 Observations of Physical and Chemical Changes

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Test 3 — Copper(II) sulphate and sodium carbonate

11. Using a measuring spoon, add 5 mL of copper(II) sulphate solution to a clean test tube.Using a different measuring spoon, add 5 mL ofsodium carbonate solution to another test tube.In your observation table, describe theappearance of each solution.

12. Write a suggestion about what you think willhappen when the solutions are combined.

13. Combine the solutions, and record yourobservations.

14. Dispose of the solutions as directed by yourteacher.

Test 4 — Copper(II) sulphate and water

15. Using a scoopula, add a small amount (the sizeof a pea) of solid copper(II) sulphate to a cleantest tube. In your observation table, describe theappearance of the substance.

16. Write a suggestion about what you think willhappen when you add water to the copper(II) sulphate.

17. Fill the test tube full of water and record yourobservations. Use a stirring rod to mix the waterand copper(II) sulphate, and record anyadditional observations.



19. Which of the changes that you observed werephysical? How do you know?

20. Which of the changes that you observed werechemical? How do you know?

Skill Practice

21. Identify two properties for each of the following.

(a) sodium carbonate

(b) white table sugar

(c) copper(II) sulphate

Forming Conclusions

22. Create a flowchart that a classmate could followin order to identify physical and chemicalchanges.

23

Figure 4.28 Adding water to copper(II) sulphate

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B9 Design a Lab

Elements, compounds, and mixtures are part ofeveryday life. From the kitchen to the chemistry lab,we make use of different substances for theirdifferent properties.

QuestionHow can you use chemical and physical propertiesto distinguish among common substances?

Design and Conduct Your Investigation

1. Choose at least three substances to investigate.They may be substances from your chemistrylab or from home.

2. Decide which properties you will investigate.Select some from the list below, or add others.

• colour and lustre

• combustibility

• conductivity

• density

• hardness

• melting point

• solubility

• texture

• reaction with acid

• reaction with water

3. Have your teacher approve your list of testsubstances and the properties you wish toinvestigate.

4. Plan your procedure. Think about thesequestions:

(a) How will you observe different properties,and what materials and equipment will youneed to make these observations?

(b) How will you record your results?

(c) How will you organize and present yourresults?

5. Write up your procedure. Show it to your teacherfor approval before carrying it out.

6. Carry out your procedure, and collect yourobservations.

7. Present your findings in a poster or in anotherform suggested by your teacher.

Properties of Common Substances

SKILLS YOU WILL USE� Selecting instruments and

materials� Observing and recording

observations

Figure 4.29 Common substances

Figure 4.30 Possible materials and equipment

CAUTION: Keep your hair tied back when working nearopen flames. Take note of safety precautions for thesubstances you will be working with.

Skills References 1, 2

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Knowledge1. What does a physical property describe

about a substance?

2. For each of the following substances, listfour physical properties.

(a) water

(b) iron metal

(c) baking soda (sodium hydrogen carbonate)

3. What does a chemical property describeabout a substance?

4. Identify each of the following observationsas evidence of either a physical change or achemical change.

(a) A piece of copper is heated until itmelts.

(b) A piece of aluminum corrodes in asolution of acid.

(c) A piece of paper burns in a candleflame.

(d) A piece of plastic is stretched until itbreaks.

(e) Table salt boils at 1465°C.

5. From the following list, indicate whichitems would make good conductors.

(a) copper

(b) Styrofoam®

(c) iron

(d) woollen mitten

6. What is the difference between theproperties of ductility and malleability?

Connect Your Understanding7. Would you rather mop up spilled milk with

a paper towel or a plastic bag? Use theterms “adhesion” and “cohesion” to explainyour choice.

8. Identify each of the following as astatement that describes either a physicalproperty or a physical change.

(a) Ice melts.

(b) Hydrogen is a colourless gas.

(c) You chop a carrot.

(d) A diamond jewel is hard.

(e) Copper wire bends easily.

(f) The ruby slippers are red.

9. Examine this photographof the graduatedcylinder. Whatproperties of water allowit to form a meniscus(the curve in the water)?

10. Use diagrams andcaptions to explain whathappens to the particles of matter in each ofthe following situations.

(a) Butter melts.

(b) Water boils on a stove.

(c) Water vapour in the air cools and formsraindrops.

11. Do water and vegetable oil have the samefreezing point? How do you know for sure?

Reflection12. Name an object that you use every day,

such as earphones, a plastic mug, or yourtoothbrush. What would you like to findout about this object’s properties now thatyou have completed this section?

For more questions, go to ScienceSource.


Question 9

4.2 CHECK and REFLECT

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For Dr. Lee Wilson, chemistry is not just a researchsubject — it is a source of solutions to problemsthat touch our lives. Dr. Wilson is an award-winning professor of chemistry at the University ofSaskatchewan, where he teaches and conductsresearch (Figure 4.31). He hopes his work willmade a big difference in medical andenvironmental science.

Dr. Wilson’s special interest is in nanostructuredmaterials. Nanostructured materials are madefrom components too small to be seen even with alight microscope. These components, which areless than 0.0001 mm in size, are very useful formaking membranes with tiny pores. Suchmembranes can be used as filters to purify waterof toxic chemicals.

The opaque white material looks very ordinary,despite its special properties. Dr. Wilson says thatthe material acts like a sponge. Instead of trappingwater, however, the material traps small particles,such as contaminants.

Personal experience has been a majormotivating factor in Dr. Wilson’s work. Whileworking in rural Alberta, his father becamedangerously ill due to contaminated water and hadto have surgery. Dr. Wilson would like to see hisresearch used so that even remote communitiescan protect their water supplies.


Figure 4.31 Dr. Lee Wilson wants his research to make adifference in the world.

Dr. Wilson feels it is important to be a scientistwith a conscience. Scientists should do work thatbenefits society as a whole, he says.

He also says it is important to follow yourpassion. “When I have a passion for something,whether it be a problem to solve or an idea ofinterest, it is the passion that carries me throughthe hardship, despite how difficult the challengesin solving the problem or learning a new skill maybe.” Dr. Wilson was the first in a small Metiscommunity in Manitoba to go to university, the firstin his family to complete a university degree, andthe first Metis student to get a PhD from theUniversity of Saskatchewan.

Today he mentors young Aboriginal studentsparticipating in science fairs and camps and hisown graduate students (Figure 4.32). His advice toyoung scientists is to get a good education, take lotsof science courses, but also to take courses in thearts. Scientists need to be able to communicate, hesays, not just do research in a lab.

Questions

1. How is Dr. Lee Wilson’s work being applied toimprove the environment?

2. ScienceSource Use the Internet to researchnanostructured materials. What arenanostructured materials, and how are theydifferent from other substances?

CAREERS in ScienceInvestigating

Great CANADIANS in Science Lee Wilson

Figure 4.32 Dr. Lee Wilson working with his students

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Lost Wax — Found Metals

Imagine sculpting a beautiful object or statue inclay and then transforming it into a single solidpiece of metal. This is the job of a foundry artisan.A foundry artisan is a master of both the art andscience of manipulating matter. A foundry is aplace where metals such as gold and iron arefashioned into specialized parts. The metal is firstmelted until it becomes a liquid and then pouredinto a mould where it can harden and take on anew shape. An artisan adds creativity to theprocess, often making one-of-a-kind pieces of art.

It may take an artist a week or a month tomake a clay sculpture. When it is ready, thesculpture is brought to a foundry, where the workis completed. The clay sculpture is covered withsilicone rubber to form a mould. The mould is a“negative” version of the clay sculpture. Hot wax ispoured into the mould to coat the inside. This stepis repeated until a “positive” version of the claysculpture has been created. This looks just likethe original clay sculpture. A second negative ofthe sculpture is made by coating the wax with aceramic material, which is a solid that canwithstand the heat of molten metal without

breaking. Melting away the wax creates an emptyvessel into which molten metal can be poured.

One major step remains before the cast metalpiece of art is complete. A hot furnace is used toheat aluminum, silver, iron, or gold until it melts.The metal is then poured into the empty mould,where it takes on the shape of the original claysculpture (Figure 4.33). After allowing the mouldto cool slowly, it is removed and the metal piece issanded and polished to add the finishing touches.The cast metal art is now ready for sale orshipping to the museum or person whocommissioned it (Figure 4.34).

The work of a foundry artisan takes acombination of skills and talents. Being able tovisualize the finished product from the start isimportant. A foundry artisan is creative, paysattention to detail, and has the self-discipline tomeet deadlines. Also, an artisan must know howto work safely in the foundry.

Most artisans apprentice with an expert inorder to learn the specific skills they need forfoundry work. Many have been to art college orstudied the arts in university. It is common forartisans to be self-employed, and so basicbusiness training can be helpful.

Questions

1. The process of casting a piece of artwork inmetal involves making several positive andnegative versions of the final cast object.Sketch a flow chart that identifies these steps.

2. ScienceSource Research where you can takecourses in jewellery casting or foundry art.

Figure 4.33 Foundry artisans working with hot liquid metal

Science in My FUTURE The Art of Chemistry

Figure 4.34 The final product

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Key Concept Review1. What is the main difference between a pure

substance and a mixture? Name an exampleof each.

2. What is a chemical change?

3. In the following diagram, what change ofstate does each letter indicate?

4. Low-density polyethylene is a plastic thatcan be stretched somewhat withoutbreaking it. Why is this property useful fordisposable shopping bags?

5. Explain the difference between cohesionand adhesion, using an example.

6. Explain why particles of water in the aircan form frost on a cold window.

7. Name a physical property that is:

(a) shared by gold, copper, and iron

(b) shared by gold and copper but not iron

(c) shared by diamond and glass

(d) not shared by diamond and glass

8. What are two physical changes that coolinga hot substance may result in?

9. For each example, identify whether theproperty described is chemical or physical.Justify your answer in each case.

(a) Bronze metal has a shiny lustre.

(b) When silver nitrate is added to calciumchloride, a cloudy solid (precipitate)appears.

(c) Mercury is liquid at room temperature.

Connect Your Understanding10. Identify the processes shown in the

following photographs as chemical changesor physical changes. Justify your answers.

(a)

(b)

(c)

t

c

k

k

k

c

k

k

k

k

ACHIEVEMENT CHART CATEGORIES

Knowledge and understanding Thinking and investigation

Communication Applicationac

tk

4 CHAPTER REVIEW

(a)

liquid

(f)

(b)

(d)

(c)

(e)solid gas

Question 10

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11. Why will water form droplets on a smoothsurface, such as a countertop?

12. Classify and compare the followingmixtures.

(a) a drink made by dissolving drinkcrystals in water

(b) a cup of tea with tea leaves in it

(c) tomato juice

13. How can the application of heat result in achemical change? Explain, using anexample.

14. Metal foams are 75 to 95 percent air. Whateffect does this have on the density of metalfoam compared to solid metal?

15. If water freezes inside of a building’s waterpipes, the pipes may burst. Explain whythis happens.

16. Some types of clear plastic can be used tomake lenses. List three important propertiesof plastic that make it suitable for use ineyeglass lenses.

17. Winter car tires are made from a soft typeof rubber that remains flexible, even in icytemperatures. Winter tires also havedeeper grooves than all-season tires. Doyou think people should be required bylaw to have winter tires for their vehicles?Why or why not? Support your responsewith a discussion of the properties ofrubber tires.

18. List five items you have used today. Try toidentify one substance that each item ismade from and the property or propertiesthat make that substance useful. Forexample:

cellphone — plastic — lightweight and hard

19. Maple syrup comes from the sap that flowsin maple trees. The sap is collected and thenboiled so that much of the water it contains

will evaporate. Boiling off the waterincreases the sugar concentration of thesyrup and makes the syrup more viscous.Describe what is happening to the particlesin the syrup at each stage in the process.

20. Consider a homogeneous mixture, such as asalt solution, and a heterogeneous mixture,such as rice and pebbles. Suggest andcompare how you could separate thesubstances within each type of mixture.

Reflection21. Describe something that you did not know

before reading this chapter about howpeople change the properties of matter.

22. How has your opinion of the use ofchemicals in our society changed sincecompleting this chapter? c

c

a

c

a

c

a

a

t

a

a

a


Reflect and Evaluate

Review the “Language of Chemistry” chart youmade at the beginning of the chapter. How did thestrategies for finding word meanings help you toadd definitions and explanations of new terms inthe “During Reading” section of the chart?Compare your chart and use of strategies with apartner, and discuss how each strategy helpedyou to get a clear picture of new vocabulary.

After Reading

Unit Task Link

What steps should you take before investigatingthe properties of different substances? List someof the physical and chemical properties that youcould investigate in the Unit Task, for which youwill design a toothpaste. Make a list of safetyprecautions that you and your lab partners willneed to follow.

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