bcs g8 u3c07 j27 - weebly

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Pure oxygen in liquid form

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241

Key Ideas

7

9

8

Kinetic molecular theoryexplains the characteristicsof solids, liquids, and gases.

7.1 States of Matter7.2 Fluids and Density

Fluids are affected by forces,pressure, and heat.

8.1 Forces8.2 Pressure 8.3 Viscosity, Adhesion,

and Cohesion

There are both natural andconstructed fluid systems.

9.1 Fluids Under Pressure9.2 Constructed Fluid Systems 9.3 Natural Fluid Systems

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H uge glowing clouds of steam and smoke flow upward as the spaceshuttle Discovery lifts off into a clear, blue sky. The huge, orange,

external fuel tank holds a massive amount of liquid rocket fuel includingover 1.9 million litres of liquid oxygen and liquid hydrogen. Whencombined in the right proportions, hydrogen and oxygen are highlyexplosive, which makes them an excellent rocket fuel.

Hydrogen and oxygen cannot be taken into space in their gaseousform because they would take up too much space. Compressing thegases involves placing pressure on them and squeezing them into asmall space. The oxygen and hydrogen are compressed to such anextent they become liquid. This compressing process actually createsheat. The heat is removed with special devices called heat exchangers.The resulting liquid oxygen (–183°C) and hydrogen (–253°C) areextremely cold, so the external tank must be insulated.

The launch of space shuttle Discovery, July 26, 2005

Hydrogen Oxygen

242 MHR • Unit 3 Fluids and Dynamics

• At room temperature andpressure, hydrogen is a gas.

• Hydrogen is highly flammableand burns with an invisible flame.

• At room temperature and pressure, oxygen is a gas.

• Pure oxygen is nonflammable,but it can make other substancesmuch more likely to burn.

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internet connect

Did you know that the spaceshuttle toilet does not flushwith water? The toilet flusheswith air. Find out how thespace shuttle “air toilet”functions. Start your search atwww.bcscience8.ca.

Can You Lift the Can? Find Out ACTIVITY

If NASA did not insulate the external fuel tank, two problemswould occur. First, the liquid fuels could warm up enough tochange into gas. This would increase the pressure inside the tank,causing it to explode. Second, a tank without insulation would beso cold that water in the atmosphere would freeze onto the side ofthe tank immediately. This effect would be similar to the frost youhave seen build up on windows in winter. If ice formed on theexternal fuel tank, pieces of ice could fall off during launch anddamage the shuttle.

We would not be able to travel into space withoutunderstanding how fluids behave. The better we understand thecharacteristics of fluids, the better we can predict their behaviourand make use of their forces.

Unit 3 Getting Started • MHR 243

Word Connect

Dynamics is a branch ofscience that studies howmaterials move under theaction of forces.

In this activity, you can use your understanding ofchanges of state to try to lift an empty soup canwithout touching it.

Materials • crushed ice or small ice cubes• 100 mL beaker• empty soup can• water• salt• teaspoon

What to Do1. Place an empty soup can upside down on your

desk. Put 5 mL (1 tsp) of water on the soup can (inthe middle).

2. Put the beaker on top of the can and the water.Make sure the beaker sits flat against the soupcan. Fill the beaker about one third full with ice.

3. Add two heaping teaspoonfuls of salt to thebeaker. Stir the salt-ice mixture gently. Make sureyou do not move the beaker while stirring. Observethe sides of the beaker carefully while stirring.

4. Stop stirring after 3 min. Gently grab the top of thebeaker, and lift.

5. Clean up and put away the equipment you haveused.

What Did You Find Out?1. How did the sides of the beaker change during

your stirring?

2. How did you think the temperature of the ice-water mixture changed as salt was added?

3. (a) Were you successful at lifting the can?

(b) Why or why not?

4. Draw a labelled illustration of your experimentusing the terms solid, liquid, condensation,melting, and solidification.

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G lass is a marvellous substance. When it is cool and in solid form, it isrigid, clear, and breakable. But when it is heated to about 1000°C, glass

becomes molten and flows—it becomes a fluid. When it is a fluid, artists can shape it to create beautiful works of art. This process is not as easy as itsounds—you must practise for years in order to control the heating and flowof the glass.

In this chapter, you learn how the particles in matter behave and respondwhen energy is added to them or removed from them.

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What You Will Learn

In this chapter, you will • distinguish among solids, liquids, and

gases• predict how solids, liquids, and gases

change when energy is added or removed• describe differences between mass,

volume, and density• determine the density of various

substances

Why It Is Important

Understanding how particles move in differentstates of matter helps determine how materialscan be used. Thermal expansion affects thedesigns of buildings, roads, bridges, andmachines. Density can be used to identifysubstances.

Skills You Will Use

In this chapter, you will• model evidence of the space between particles• observe evidence of thermal contraction and

expansion• communicate your knowledge of fluids• measure density of fluids and solids• predict layering of fluids

Chapter 7 Kinetic molecular theory explains the characteristics of solids, liquids, and gases. • MHR 245

FOLDABLES TM

Reading & StudySkills

Make the following Foldable to help you study

the changes of state in water.

STEP 1 Fold a vertical sheet of paper from left to righttwo times. Unfold.

STEP 2 Fold the paper in half from top tobottom two times.

STEP 3 Unfold and draw lines along thefolds.

STEP 4 Label the top row and first columnsas shown below.

Read and WriteAs you read the chapter, define the states ofmatter in the Define States column of yourFoldable. Write what happens when heat isadded to or lost from each state.

On the back of the paper, illustrate the mainpoints of the kinetic molecular theory using theterms from the front of the paper.

DefineStates + Heat – Heat

Water as aSolid (Ice)

Water asa Gas

LiquidWater

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According to the kinetic molecular theory, all matter is made up of very small particles

that are constantly moving. The more energy the particles have, the faster they can

move and the farther apart they can get. Matter expands when its temperature is

raised and contracts when its temperature is lowered. If enough energy is added to

or removed from matter, the matter changes from one state to another.

Oxygen, glass, and water are all examples of matter. Matter isanything that has mass and volume. Mass is the quantity of matterthat a substance or object contains; the more matter, the greater themass. For example, a bowling ball has more mass than a basketball(Figure 7.1). Mass is usually measured in grams (g) or kilograms (kg).

Volume is the amount of space taken up by a substance or object.For example, a basketball has a greater volume than a bowling ball.The volume of a liquid is usually measured in millilitres (mL), litres (L), or cubic centimetres (cm3).

Recall from earlier studies that there are three familiar states (phases) of matter:• Solid is the state of matter that has a definite shape and volume

(for example, a bowling ball).• Liquid is the state of matter that has a definite volume, but its

shape is determined by its surroundings (for example, water in a beaker).

• Gas is the state of matter that has its volume and shape determined by its surroundings (for example, helium in a balloon).

States of Matter7.1

Figure 7.1 A bowling ballhas more mass but lessvolume than a basketball.

Did You Know?

Key Termscondensationevaporationexpansion massmeltingsolidificationsublimationvolume


In the past, there has been somequestion as to the physical stateof glass. It has been argued thatglass is a very stiff liquid. Glass isnow known to be a type of solidcalled an amorphous solid.

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All solids, liquids, and gases are made of very smallparticles that have spaces in between them. In thisactivity, you will model evidence of the spaces .

Safety

• Ethanol is poisonous.

• Be careful to wipe up any spills.

Materials • funnel• water• two 100 mL graduated cylinders• 250 mL graduated cylinder• 50 mL ethanol• marbles• 50 mL sand

• stirring rod

What to Do1. Copy the following data table.

Trial 1 Water and Water

2. Use a funnel to carefully measure 50 mL of waterinto each of the two 100 mL graduated cylinders.

3. Predict the total volume you will have when you combine these two volumes.

4. Add one of the volumes of water to the other.Stir with the stirring rod. Record the totalvolume.

Trial 2 Water and Ethanol

5. Carefully measure 50 mL of water into one 100 mL graduated cylinder and 50 mL of ethanolin the other cylinder.

6. Predict the total volume you will have when you combine these two volumes.

7. Add one of the volumes to the other. Stir withthe stirring rod. Record the total volume.

Trial 3 Marbles and Sand

8. Add marbles to the 250 mL graduated cylinderuntil they reach the 50 mL mark.

9. Predict what the new volume will be when youadd 50 mL of sand to the marbles.

10. Add 50 mL of sand. Record the new volume.Save the mixture for Trial 4.

Trial 4 Marbles, Sand, and Water

11. Predict what the new volume will be when youadd 50 mL of water to the marbles and sand.

12. Add 50 mL of water. Record the new volume.

13. Clean up and put away the equipment you have used.

What Did You Find Out?1. If the 50 mL of water and 50 mL of water did not

add up to 100 mL, explain why.

2. If the 50 mL of water and 50 mL of ethanol didnot add up to 100 mL, explain why.

3. If the 50 mL of marbles and 50 mL of sand didnot add up to 100 mL, explain why.

4. If the 50 mL of marbles, 50 mL of sand, and 50 mL of water did not add up to 150 mL,explain why.

5. If you had added the substances in Trial 3 to thecylinder in reverse order, would the total volumebe greater or less? Explain.

Modelling the Particle Model 7-1 Find Out ACTIVITY

Trial Volumes Predicted Total Actual Total Volume (mL) Volume (mL)

1 50 mL water50 mL water

2 50 mL water50 mL ethanol

3 50 mL marbles50 mL sand

4 Trial 3 plus 50 mL water

Go to Science Skill 8 for help in usingmodels in science.

Science Skills

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The Particle Model of MatterWhy can certain materials slip and slide past other materials? Theanswer can be explained by looking at tiny particles of matter. Infurther studies, you will learn about atoms and molecules. These atoms and molecules are the tiny particles of which matter is made (see Figure 7.2).

In earlier studies, you may have learned about the particle modelof matter:1. All matter is made up of very small particles. The particles are

much too small to observe with the naked eye or with a lightmicroscope.

2. There are spaces between the particles. The amount of spacebetween the particles is different for different states of matter. For example, gases have much more space between particles than solids do.

3. The particles that make up matter are always moving.4. The particles are attracted to one another. The strength of the

attraction depends on the type of particle.

Figure 7.2A The particles in asolid are packed together tightly.This means that solids will hold adefinite shape. Even though a soliddoes not appear to move, theparticles are constantly vibrating inplace.

Solid Gas

Figure 7.2B The particles in a liquidare in contact with each other, but theycan slip and slide past one another,changing their position. This slipping andsliding means liquids take the shape oftheir container.

Figure 7.2C Gas particles have verylarge spaces between them. In fact, gasesare mostly empty space. Gases are quitedifferent from liquids and solids becausethe particles in a gas can move freely inall directions. This is why gases alwaysspread out or diffuse in their container.

Liquid

Did You Know?

How small are molecules? A small drop of water has about 1 sextillion (1 followed by 21 zeroes!) water molecules.

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The Kinetic Molecular TheoryKinetic energy is the energy of motion. All particles in every solid,liquid, and gas are always moving, so they have kinetic energy.Scientists have expanded the particle model and developed the kineticmolecular theory to explain what happens to matter when the kineticenergy of particles changes. A model in science is a way to think aboutand interpret natural events and objects. A theory provides a scientificexplanation based on the results of experimentation.

Reading Check

1. How is a solid different from a liquid in shape and volume?2. How are liquids and gases similar in shape and volume?3. How are liquids and gases different in the amount of space

between particles?4. How does the behaviour of particles change as energy is added to

them? How does the behaviour change as energy is lost?5. How does the space between particles change as energy is added

to them? How does the space change as energy is lost?

The main points of the kinetic molecular theory include:1. All matter is made up of very small particles (atoms and molecules).2. There is empty space between particles.3. Particles are constantly moving. The particles are colliding with each other and the

walls of their container.

(a) Particles of a solid are so tightly packed together they cannot move around freely. They can only vibrate.

(b) Particles of a liquid are farther apart and they can move by sliding past each other.

(c) Particles of a gas are very farapart and they move aroundquickly.

4. Energy makes particles move. The more energy the particles have, the faster theycan move and the farther apart they can get.

Find Out Activity 7-2 onpage 254

Suggested Activity

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Thermal Expansion and ContractionWhen you add energy to a material, you increase the kinetic energy of the particles. A common way to add energy is to add heat. Whathappens inside a solid, liquid, or gas as its temperature goes up? As the temperature of a solid, liquid, or gas increases, its particles movearound faster. Each particle moves over a larger region, which resultsin more space between particles. The material that is made up of theparticles expands. In other words, it increases in volume. In general,any kind of matter expands when its temperature increases. This effectis called thermal expansion.

What do you think happens to matter when its temperaturedecreases? The movement of the particles slows down, which meansthe particles take up less space as they lose energy. The mattercontracts, or in other words, decreases in volume. This effect is calledthermal contraction.

Different materials expand or contract with changing temperatureat their own particular rate. An aluminum rod, for example, expandsabout three times more than a glass rod for the same change intemperature.

You might have observed that a hot drinking glass shatters when it is placed in cold water. Why do you think this happens? When ittouches the cold water, the glass begins to contract. However, glassdoes not conduct heat well, so parts of the glass that are not yet incontact with the water remain expanded. The uneven contraction cancause enough stress to break the glass. Laboratory glassware is made of a special glass that expands much less with temperature changesthan ordinary glass. The smaller amount of thermal expansion makeslaboratory glassware less likely to break when heated or cooled rapidly.

Figure 7.3 shows several uses of thermal expansion andcontraction.

Figure 7.3A A thermometer indicatestemperature through the expansion andcontraction of a liquid. Because of thenarrow tube, the liquid has to expandonly slightly to show a large change onthe temperature scale.

Figure 7.3B As the coolant in a carbecomes hotter, it expands. Theplastic container shown aboveprovides extra space for the hotcoolant to seep into. When the engineis cool, the coolant contracts and nolonger overflows into the container.

Figure 7.3C Highways and bridgesmust be built with gaps to allow theexpansion of the pavement.

Word Connect

The word “kinetic” comesfrom a Greek word meaningmotion or movement. Thesame Greek word is the basisof the word “cinema”(moving pictures).

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hightemperature

lowtemperature

heatheatheat

internet connect

An artisan heats metal sothat it is easier to shape intojewellery. To learn moreabout artisan work withmetal, visitwww.bcscience8.ca.


Figure 7.4 Energy is transferred between two objects with different temperatures.

The Difference Between Heat and TemperatureIf you consider all the kinetic energy of all the particles of a substance,the total amount of energy will be the thermal energy of the substance.If two substances with different thermal energies come into contact,energy will always flow from high to low thermal energy (see Figure 7.4).Heat is the energy transferred from one material or object to anotheras a result of a difference in temperature or a change in state.

As an example, think about what happens when you touch a warmcup of tea. The cup has higher thermal energy than you; when youtouch it, you can feel the heat transfer from the cup to your hands. Ifyou hold a thermometer bulb as your hands warm up, you would seethe temperature increase as the total kinetic energy of the particlesthat make up your hands increases. When you take a temperaturereading from a substance, you are “sampling” the average kineticenergy of its particles. Figure 7.4 shows the transfer of energybetween two objects with different temperatures.

Reading Check

1. What is the difference between a model and a theory?2. What happens to matter when its temperature increases?3. What happens to matter when its temperature decreases?4. What is the difference between heat and temperature?

Conduct an Investigation 7-3on page 255

Suggested Activity

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Figure 7.5A Changes of state

Changes of StateWhat happens to matter if its temperature continues to rise or fall? Asthe space changes between the particles, so does the state of matter.

When the temperature of a solid is raised, the particles becomemore energetic, and they move farther and farther apart. If enoughenergy is added, the solid melts. Melting is the change of state of asubstance from a solid form to a liquid form. If enough energy isadded to the liquid, it evaporates. Evaporation is the change of stateof a substance from liquid form to gas form.

When the temperature of a gas is lowered, the gas condenses.Condensation is the change of state of a substance from gas form toliquid form (see Figure 7.5A). If enough energy is removed from theliquid, it solidifies. Solidification is the change of state of a substancefrom liquid form to solid form.

Sublimation is the change of state of a substance directly from asolid form to a gas form. The opposite of sublimation is deposition.An example of deposition is when frost forms on windows on verycold days. See Figure 7.5B for an example of sublimation.

All substances have different specific temperatures at which theychange state. The melting point is the temperature at which a solidturns to liquid (see Figure 7.6 on the next page). The boiling pointis the temperature at which a liquid turns to gas.

subli

mation

depo

sition

condensation

evaporation

solid

gas

liquid

melting

solidification

Word Connect

You can find condensation atwork in your school library.The word “condense” candescribe writing something infewer words. A condensedversion of a book may haveonly half the amount of wordsas the original book.

Figure 7.5B Dry ice is often used inspecial effects to make fog. Dry ice is solidcarbon dioxide, which sublimes from asolid to a gas. Dry ice is much colder thanregular ice, so it condenses the moisture inthe surrounding air into small waterdroplets we see as fog.

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5. Gaseous lead.All particles are highly energetic and move freely to spread out intheir container. Further heating givesparticles even more kinetic energy,making the gas spread out fasterand farther.

Reading Check

1. How does matter change from one state to another?2. What is the relationship between the amount of space between

particles and the state of the matter?3. What is the difference between evaporation and sublimation?4. How is melting similar to solidification? How is it different?

1. Solid leadParticles are very close to oneanother, fixed in position,and vibrate.

2. Melting leadParticles vibrate more, collide with each other, and make more space between them.

3. Liquid leadAll particles are still close, but now have enough space to slidepast one another.

4. Boiling leadHighly energetic particles bouncevigorously against each other,creating more space. Someparticles gain enough energy to break completely free of theliquid lead.

Find Out Activity 7-4 on page 256

Suggested Activity

Changes of State in Lead

Figure 7.6 Energy added to lead (shown by orangearrows) causes a change of state.

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Find Out ACTIVITYCool Contraction7-2

Teacher DemonstrationIn this activity, you can observe evidence that a gascontracts when it cools.

Safety

• Be careful when handling hot water.• Be sure that the flask does not have

any chips or cracks.

Materials • flask• small balloon• large bowl• ice• protective mitt• cold water• very hot water

What to Do1. Fill the bowl halfway with ice. Put cold water into

the bowl to create an ice water bath.

2. Fill the flask with hot water and let it sit for 3 min.

3. Use the protective mitt to pour the hot water outof the flask. Immediately stretch the balloon overthe mouth of the flask. Caution: the mouth of theflask may be hot.

4. Place the flask into the ice water bath. Hold theflask upright and make sure the balloon is free tomove. You may have to hold the tip of the balloonif it is folded over the edge of the flask.

5. Be patient. It may take up to 10 min for the flaskto cool. During this time, watch the ballooncarefully.


What Did You Find Out?1. What do you think happened to the temperature

of the gas (air) inside the flask during thisexperiment?

2. How would you describe the kinetic energy of theparticles of the gas inside the flask during theexperiment?

3. How is the behaviour of the balloon related to thekinetic energy of the particles of gas inside theflask?

4. (a) How could you inflate the balloon?

(b) Explain your idea by referring to the kinetic molecular theory.

en

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Safety

• Be careful when workingwith an open flame and hotobjects.

Materials • 1 m thin (20–22) gauge

copper wire (withoutinsulation)

• small hooked mass (200 gor 500 g)

• metre stick• 2 lab stands• 2 C clamps• pipette or medicine dropper• lighter• long candles• ice water• aluminum foil

In this investigation, you can measure the expansion and contraction of a wireas it is heated and cooled.

QuestionWhat evidence can you observe of solid materials expanding as they arewarmed, and contracting as they are cooled?

HypothesisComplete the following hypothesis statements:

(a) When a material is heated, it will…

(b) When a material is cooled, it will…

Procedure1. Read the procedure steps below. Use your hypothesis to make a prediction.

What will happen to the small mass as the wire warms and cools?

2. Prepare a data table to record readings at 30 s intervals for 10 min. Giveyour table a title.

3. Clamp two supports firmly to the table 50–70 cm apart, and stretch the wiretightly between them. Wrap aluminum foil around the bottom of the candlesto catch any drips.

4. Place the small mass in the middle of the wire. Put the metre stick behindthe mass, and record the height of the mass.

5. Light the candles. Use the lighted candles to warm the entire length of thewire for several minutes. Observe and carefully record the height of themass after each 30 s of heating for 5 min. Blow out the candles.

6. Use the pipette or medicine dropper to place 5 drops of ice water along theentire length of the wire. Carefully record the height of the mass after each30 s of cooling for 5 min.

7. Clean up and put away the equipment you have used.

Analyze1. Describe what happened to the copper wire as it was heated and cooled.

2. Compare your data with that of another group. What could be the reasonsfor any differences in data?

Conclude and Apply1. Draw close-up diagrams that show how the wire changed during this

investigation. Your diagrams should be labelled and should show whathappened to the particles in the wire.

Warming Down, Cooling Up7-3

Skill Check

• Observing

• Predicting

• Measuring

• Communicating

Do not touch the hot wire.

Conduct an INVESTIGATION

Inquiry Focus


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What happens to the temperature of water as itchanges state? In this activity, you can find out.

Safety

• Be careful using the hot plate.

Materials • hot plate• 250 mL beaker• ice water• stirring rod• thermometer or temperature sensor• thermometer clamp• lab stand• stopwatch

What to Do

Part 1 Record Temperature

1. Form two hypotheses about what you think willhappen:

(a) While solid ice changes to liquid water, thetemperature will (drop/stay thesame/increase) because…

(b) While liquid water boils into gas, thetemperature will (drop/stay the same/increase), because…

2. Create a data table that will allow you to recordthe temperature every 1 min for 30 min.

3. Turn the heat on the hot plate to maximum.

4. Put about 100 mL of ice water into the beaker.Place the beaker on the hot plate. Lower theclamped thermometer into the water, but makesure it does not touch the bottom of the beaker.Begin timing.

5. Begin to gently stir the mixture of ice water.Every 1 min, record the temperature from thethermometer. Continue stirring and takingreadings until 5 min after the water beginsboiling.

6. Unplug the hot plate. Let the beaker and hotplate cool before putting them away.

Part 2 Create a Line Graph

7. Create a line graph of temperature versus timewith the data you collected.

8. Label the area on the line graph where the icewas melting (include all parts of the line graphwhere ice was present).

9. Label the area on the line graph where the waterwas boiling.

10. Label the points on the line graph representingthe times where the ice completely disappearedand where the water started to boil.

What Did You Find Out?1. (a) Describe how the temperature changed

during the time the ice melted.

(b) Describe how the temperature changedduring the time the water boiled.

2. What happened to the energy from the hot plateduring melting and boiling?

3. From your observations, write a clear answer tothe question at the beginning of thisinvestigation.

4. Do your observations support your hypotheses?Explain.

7-4 Changes of State in Water

Go to Science Skill 7 for help withmeasuring temperature. Go to Science Skill 5 for help with drawing a graph.

Science Skills

Find Out ACTIVITY


abs in

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PermafrostDid you know that permanently frozen soil underliesabout half the landmass of Canada? Permafrost isground that remains at a temperature below freezingall year long. Living with permafrost beneath youpresents some unique challenges, but offers someopportunities as well.

Aboriginal communities in Canada’s North use thepermafrost to their advantage. For example, the Inuitpractice of building community freezers in thepermafrost allows the people to keep their meat fromspoiling.

Building a home on top of permafrost requiresspecial care. Once the home is built, it can warm theground beneath it and melt the permafrost. When thismelting occurs, the permafrost transforms from a rigidsolid into a flowing mixture of solid and liquid. Thismixture can damage buildings as they sink into theground.

Global warming is causing large amounts ofpermafrost to melt. Scientists are concerned becauseonce permafrost melts, the organic matter in it beginsto decay. Decaying matter releases gases into theatmosphere that contribute to even more globalwarming. People who live on permafrost are concernedsince it means that houses will be damaged, roads willbecome impassable, and it will become very difficult totravel to hunt for food.

Questions

1. How do you think the density of permafrost changes as it melts? Use kinetic molecular theory to explain your answer.

2. If the permafrost continues to melt, how do you think it will affect Aboriginal communitiesin the Arctic?

3. If you decided to build a home on permafrost,what special measures would you take to ensure the long-term safety of the structure?

Game animals arenot wasted in Inuitculture. Unusedmeat is preservedfor later use.

Global warming ismaking arctic icemelt, reducing thehabitat for alreadyendangered species.

The ice crystals thatform in a communityfreezer are from themoisture in people’sbreath and the foodthey bring in.

A buildingsinking into thepermafrost

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PlasmaBoom! A lightning strike is a thrilling display ofnature’s power—it is also a display of a fascinatingfourth state of matter, plasma. Plasma is an ionizedgas, a “soup” of electrically charged particles. Plasmaconducts electricity very well. When a stream ofplasma forms between the ground and the cloudsduring a thunderstorm, large amounts of electricalcharge move quickly, forming lightning. Whenlightning discharges, it can reach a temperature ofover 28 000°C in a split second—that is five timeshotter than the surface of the Sun! The dischargecauses the surrounding air to explode, making thesound we hear as thunder.

Our Sun is mostly plasma, and everything visibleto us outside our solar system is plasma. Withpowerful telescopes, astronomers have taken photosof concentrations of interstellar dust and plasmacalled nebulae.

A nebula can be a birthplace for stars. Nebulae can also be formed when starsexplode.

Coloured discharges in a plasma ball

Because plasmas can reach such extremetemperatures, a plasma cutter can slice throughthings that would normally be difficult to cut,such as thick steel.

A powerfullightning strike

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Checking Concepts1. In order to turn mercury from a liquid into

a solid, you must lower its temperature toapproximately –39°C. Draw a diagram torepresent what happens to the particles ofmercury as it turns from liquid to solid.

2. Silver melts at 961°C. Some wax melts at 56°C and boils at 370°C. Is it possible to boil wax in a silver bowl? Explain.

3. Using what you know about the particlemodel of matter, explain the differences inappearance and behaviour between liquidwater and steam.

4. When hanging electrical wires in summer,workers string the wires loosely from pole topole. Why are the wires not strung tightly?

5. When holding a tall glass of iced tea on awarm day, your hand becomes cooler, whilethe glass of iced tea becomes warmer.Explain what is happening to the particles inyour hand and in the glass to account for thetemperature changes.

6. The metal lid on a jar is stuck on very tight.Use the kinetic molecular theory to explainwhether heating or cooling the lid is the bestmethod for helping to remove it.

7. Some hockey players curve the blades oftheir wooden hockey sticks by heating themand then applying force. Why do hockeyplayers not simply force the blade to bendwithout heating? Explain your answer interms of kinetic molecular theory.

Understanding Key Ideas8. Explain why water droplets form on a cold

bathroom mirror when someone has a shower. Use correct terms for the state changes that occur.

9. Global warming is an importantenvironmental concern. One particularconcern is that as the temperature of theoceans increases, water levels could rise andflood coastal communities. Explain whywarmer temperatures could lead to higherwater levels.

10. Two drinking glasses are stuck together,one inside the other. Write arecommendation for how to remove theouter glass without breaking either glass. Include the terms “thermal contraction”and “thermal expansion” in yourrecommendation.

Suppose you had a tight-fitting nut that youwanted to put onto a bolt. Would it be agood idea to heat the nut or cool it beforetrying to screw it onto the bolt? Draw apicture of the bolt and use dots to representthe particles to help you think through theproblem.

Pause and Reflect


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Fluids are forms of matter that can flow. Density is a measure of the mass contained

in a given volume. Substances with a lower density will float on substances with a

higher density.

Fluids and Density7.2

Key Termsdensitydisplacementfluid


Liquids and gases are fluids, forms of matter that can flow. In this activity, you will share your knowledgeof fluids.

What to DoDivide a piece of notebook paper into quarters. Labelthe sections Box A, Box B, Box C, and Box D.

1. In Box A, list all the fluids you can think of.

2. In Box B, suggest more than one way you can makea fluid flow more quickly.

3. In Box C, suggest several applications (uses) whereheating fluids is important.

4. In Box D, suggest several applications wherecooling fluids is important.

5. Share your information with a partner.

Fluids Can Flow7-5 Think About It

Figure 7.7 Lava flows from an erupting volcano, water flows in a mountain stream, andpancake syrup flows from its container.

What do pancake syrup, water in a mountain stream, and lava flowingfrom a volcano have in common? They are all fluids (Figure 7.7). Afluid is any form of matter that can flow. Liquids and gases are able toflow because they do not have a fixed shape. Solids have a fixed shapeand cannot flow. Therefore solids are not fluids. Your body containsmany fluids, such as blood and the watery cytoplasm inside cells. Airflows into your lungs each time you inhale, and out of your lungswhen you exhale.

ces

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Using what you already know about particles and the state ofmatter, predict which is likely to be the densest, a solid, a liquid, or agas. Take a look at Figure 7.9. Aluminum (a solid), is denser thanwater (a liquid), and water is denser than air (a mixture of gases)—butwhy? The key to density is the spacing of the particles. The particlesof a piece of solid aluminum are tightly packed, while liquid waterparticles have enough room between them to change position. Theparticles of air are free to move independently and have a largeamount of space between them. Less densely packed particles will“float” on more densely packed particles. As temperature increases, a substance will change from solid, to liquid, to gas. According tokinetic molecular theory, the particles of a substance spread out asthey gain energy when heated. The particles will take up more space,which means that the density of the substance decreases.

Most substances are denser in their solid form than their liquidform, but water is an exception. When water freezes, the particlesmove slightly farther apart as they become fixed in position. Thismeans that ice is actually less dense than liquid water, so it floats (see Figure 7.10).

Section 10.2 has moreinformation about the densityof water and ice.

Connection

Figure 7.8 When traffic gets very dense, it is difficult for vehicles to move.

Solid, Liquid, and Gas Density One property that is useful in understanding both fluids and solids isdensity. Density is the mass of a given volume. In other words, densitydescribes how closely packed together the particles are in a material.

You might think of density in terms of vehicles on a highway. Atraffic jam like the one on the left in Figure 7.8 is a model of highdensity. The photograph of free-flowing loosely packed traffic on theright in Figure 7.8 is a model of low density.

Figure 7.9 A sealed containerholds air, water, and an aluminumblock.

Figure 7.10 The property of icefloating on water makes life infreshwater lakes possible. If icesank as it froze, lakes would freezesolid. Instead, the floating ice buildsslowly from the top down, creatingan insulating barrier against coldtemperatures.

Did You Know?

There is space between grains ofsugar. When you melt sugar tomake candy, the sugar becomesa fluid. After the sugar cools, itcontracts, making the candy even more dense than theoriginal sugar.

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Generally speaking, solids are denser than liquids, andliquids are denser than gases. In this activity, you willdiscover whether a fluid could be denser than a solid.

What to DoThe approximate densities of some common substancesat 20°C are listed in the table. The higher the number,the denser the substance. Use the information in thetable to answer the following questions.

1. Which substance in the table is the densest?

2. Which substance is the least dense?

3. Which fluid is denser than lead?

4. Water is denser than which three solids?

5. (a) Which substances would float in water?

(b) Which substances would sink in water?

6. Which common metals are less dense thanmercury?

Dense, Denser, Densest7-6 Think About It

Layers of FluidsImagine two beakers, one filled with water, and one filled with cornsyrup. Does the water or corn syrup have the greater mass? Which hasthe greater density? Recall that density is the mass of a given volume.When you compare the masses of equal volumes of different kinds ofmatter, you are comparing their densities.

Some liquids float on top of others. Liquids will layer in order of density—the less dense liquid floats on the denser liquid if the twoliquids do not mix together. How would corn syrup and water belayered if they were placed in the same beaker? Even though the twoliquids are of the same volume, the corn syrup has more mass, andtherefore it has a greater density than the water. Placing them togetherin the same container would result in the water floating on top of thecorn syrup.

This layering according to density can even occur within the same substance. Air is an excellent example; differences in air densitycontribute a great deal to weather. When air is heated near the groundon a hot summer day, the particles gain energy and move farther apart. The warm air has a lower density than the air around it, and as aresult, it begins to rise (see Figure 7.11 on the next page). As thewarm air rises, cooler air rushes in beneath it, and a breeze is created.

Section 5.1 has informationabout air layers and mirages.

Connection

Fluid Density (g/mL) Solid Density (g/cm3)

hydrogen 0.00009 Styrofoam™ 0.005

helium 0.0002 cork 0.24

air 0.0013 oak 0.70

oxygen 0.0014 sugar 1.59

carbon dioxide 0.002 salt 2.16

ethyl alcohol 0.79 aluminum 2.70

machine oil 0.90 iron 7.87

water 1.00 nickel 8.90

seawater 1.03 copper 8.92

glycerol 1.26 lead 11.34

mercury 13.55 gold 19.32

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10 000 m

8000 m

2500 m

sea level


Figure 7.11 As low-density warmair rises, it can carry water vapourwith it. When the water vapourreaches the cooler higheratmosphere, it condenses into tinydroplets that we see as clouds.

Air is a mixture of many types of particles, but it is mostly made ofnitrogen and oxygen. Air particles are relatively dense close to Earth’ssurface. If we increase our altitude, we encounter areas of lower airdensity. The higher we go, the farther apart the air particles are spreadout, making it harder for us to get enough oxygen particles into ourlungs with every breath (see Figure 7.12).

Reading Check

1. Explain why gases and liquids are called fluids, but solids are not. 2. What happens to the density of matter when the matter is heated?3. Why does ice float on water?4. Why does water float on corn syrup? 5. How is a breeze created over land on a hot summer day?6. Why is there more oxygen available to breathe at sea level than

there is higher in the atmosphere?

Figure 7.12 At sea level (A), there are more than enough oxygen molecules for us to breathe. Most people can climb to 2500 m with no ill effects (B). But going higher will likelylead to symptoms of lack of oxygen. Oxygen masks are needed at this air density (C). Largeairplanes fly at high altitude because the air density is very low (D). With so much empty space between the particles, the airplane encounters less air friction, making flying moreefficient and requiring less fuel.

Find Out Activity 7-8 on page 268

Suggested Activity

Did You Know?

The cabins in large airplanes are pressurized so that the airdensity in the airplane is similarto the density on the ground.If the airplane loses cabinpressure, oxygen masks drop tothe passengers, providing themwith the oxygen they need.

D

C

B

A

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Measuring Density Layering is a useful technique for comparing densities (see Figure7.13). When an object is placed in a less dense fluid, the object willsink down toward the bottom. If the fluid is denser than the object,the object will float. If the object has the same density as the fluid, theobject will “hover” in place. Layering allows you to determine whetherone substance is denser than another substance. However, layeringdoes not provide a specific measurement of density, and layeringcannot be used with solids. Solids do not flow, and their particles areso close together that other substances cannot move through them.How can you measure the density of a substance?

Recall that density is the mass of a given volume. To find thedensity of a substance you need to know its mass and its volume. Masscan be determined using an electronic scale or balance (see Figure 7.14).

The volume of a solid is often measured in cubic centimetres (cm3).A cubic centimetre is the volume of a cube that measures 1 cm oneach side. In other words, the volume of an object equals the numberof 1 cm cubes it takes to fill that object. The volume of an object thathas a simple shape can be determined mathematically (Figure 7.15).

Figure 7.13 The SuperBall® sinksin the oil, but floats on the water!

Figure 7.15 For objects that are block-shaped, volume canbe calculated mathematically by using the equation:volume � length � width � height.

Figure 7.14 This triple beam balance indicates theapple has a mass of 94 g.

Reading Check

1. How can you find the volume of a rectangular solid?2. How can you find the volume of an irregularly shaped solid? 3. What two measurements do you need in order to calculate

density?4. What is the volume of a rectangular box that is 10 cm long, 5 cm

wide, and 2 cm high?

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Practice Problems

1. What is the density of a 2 cm3 sugar cube that has a mass of 3.18 g?

2. A 3 mL sample of oil has a mass of 2.64 g. What is the density of the oil?

3. The mass of 1 cm3 of lead is 11.34 g. The mass of 1 cm3 of iron is 7.87 g.Which solid has the greater density?

Density and Dinosaurs

The densest substance thatoccurs in nature is iridium, ahard, brittle, whitish-yellowmetal, with a density of 22.65 g/cm3. Iridium has aspecial connection to the endof the reign of dinosaurs onEarth. Find out more aboutiridium and its connection todinosaurs. Start your search atwww.bcscience8.ca.

Answers

1. 1.59 g/cm3

2. .88 g/mL 3. lead

DisplacementHow would you measure the volume of an object with an irregularshape? Displacement is the amount of space that an object takes upwhen placed in a fluid. Have you ever noticed how the water level rises in a bathtub when you get into it? The amount of water you are displacing is the volume of your body that is in the water. So bymeasuring the displacement of an object, you can measure the volumeof the object.

Calculating Density Once you know the mass and the volume of a substance, you cancalculate the density. You can calculate the density of both fluids andsolids. The units for density depend on how you measure the mass andvolume of your objects. The density of fluids is usually measured ing/mL, while the density of solids is usually measured in g/cm3

(1 mL has the same volume as 1 cm3).

density (D) �

Read the question:

1 mL of glycerol has a mass of 1.26 g. What it the density of glycerol?

Use the formula:

D �mV

�

State your answer:The density of glycerol is 1.26 g/mL.

mass (m) volume (V)

1.26 g1 mL

BCS_G8_U3C07_J27 5/8/06 10:27 AM 5


Safety

• Handle balances with careand use them as instructedby your teacher.

• Avoid spilling fluids andsolids on the balances.

• Do not pour materialsdown the drain. Dispose ofthem as instructed by yourteacher.

• Use only fluids that arefoods or mild dishdetergents. Do not use anyfluids that have any type ofdanger symbol on theirlabels.

In this investigation, you can make and use accurate measurements todetermine density and predict layering.

QuestionWhat are the densities of various fluids and solids?

Materials • various fluids, such as water, vegetable oil, corn syrup, molasses, dish

detergent• various granular solids, such as sand, sugar, flour, aquarium rocks• various solid objects, such as an eraser, pencil sharpener, block • large graduated cylinder• overflow can• water• 250 mL beaker• clear plastic disposable drinking cups• electronic scale or triple beam balance• medicine dropper • ruler• calculator

Procedure

Part 1 Calculating Density

1. Copy the data table below to use in recording your experimental data.

Density Mystery

Material Mass of Mass of Mass of Volume DensityGraduated Graduated Material (mL or (g/mL or Cylinder Cylinder and (g) cm3) g/cm3)

(g) Material (g)

7-7

Skill Check

• Measuring

• Classifying

• Explaining systems

• Evaluating information

Go to Science Skill 7 forhelp with measuring massand volume. Go to ScienceSkill 5 for help withdrawing a graph.

Science Skills

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2. Use measurement A, B, or C to determine the mass and volume of each material.

Measurement A: Use for fluids and granular solids.

(a) Place the empty graduated cylinder on thescale. Record its mass.

(b) Fill the graduated cylinder to the 25 mLmark. Use the medicine dropper if necessary.Record the volume of the fluid or granularsolid as 25 mL.

(c) Place the filled graduated cylinder on thescale and record the mass of the fluid orgranular solid and cylinder.

(d) Subtract the mass of the empty graduatedcylinder from the mass of the filledgraduated cylinder. This is the mass of thefluid or granular solid. Record the mass inyour table.

Measurement B: Use for solids that are cubic orrectangular.

(a) Place the solid on the scale. Record its mass.

(b) Use the ruler to measure the length, width,and height of the solid in centimetres.

(c) Multiply the length, width, and heightvalues together. This is the volume of thesolid. Record the volume in your table.

Measurement C: Use for irregularly shaped solids.

(a) Place the solid on the scale. Record its mass.

(b) Position the beaker to catch water from theoverflow can. Fill the overflow can withwater. Empty the beaker of any water thathas overflowed and place it back intoposition to catch water.

(c) Push the solid into the water of theoverflow can so that it is just underwater.Pour the beaker overflow water into thegraduated cylinder. The reading on thecylinder is the volume of the solid. Recordthe volume in your table.

3. Divide the mass of each material by its volume.This is the density of the fluid or solid. Recordthis density in your table.

Part 2 Comparing the Materials

4. Examine the densities of the materials in thedata table. Create a bar graph that compares all the densities.

5. Examine your bar graph. Predict how thesefluids would layer if you put them into the sameclear plastic cup. Make a sketch that illustrateshow you think the fluids would layer.

6. Carefully pour each fluid you tested into a clearplastic cup in the order you predicted in step 2.Start with the fluid at the bottom. Use onlyenough fluid to create a layer approximately 1 cm deep. Tilt the cup as you pour to allow thefluids to layer and avoid splashing.

Analyze 1. (a) What parts of this density experiment

could have caused experimental error?

(b) How might you do the experimentdifferently to reduce that error?

2. Compare your density results and layering testto the predictions you made. If you were wrongon any prediction, offer an explanation why.

Conclude and Apply1. (a) Write a short paragraph that describes how

you can determine the density of a fluid orsolid. Include an evaluation of two differentdensity-determining techniques.

(b) Is one technique better than the other?Why?

Conduct an INVESTIGATION

Inquiry Focus

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In this activity, you can find out how the temperatureof a liquid affects its density.

Safety

• Be careful when handling hot water.

Materials • two 250 mL beakers • stirring rod• very cold water • large spoon• very hot water • food colouring

What to Do 1. Add 100 mL of water to a beaker. Use water as

cold as possible from the tap.

2. Add 100 mL of water to the other beaker. Usewater as hot as possible from the tap. Do not burnyourself. Use protective mitts to handle your hotwater beaker.

3. Add a few drops of food colouring to the hot waterand stir.

4. Put the stirring rod across the top of the hot waterbeaker, and very gently tip it so that the water runsalong the stirring rod into the cold water beaker.

5. To make sure the hot water enters gently, haveyour partner hold the head of the spoon at the topof the cold water level. Pour the hot water into thehead of the spoon. Continue pouring very slowlyuntil the beaker is full.

6. Observe your beaker. If you have created twolayers, look at them very carefully, especially wherethe two layers meet. If you do not have two layers,look at the beakers of other students in class.


What Did You Find Out?1. How does the density of hot water compare to the

density of cold water?

2. Occasionally this experiment is unsuccessful withthe hot and cold water not forming layers. Offer aparticle explanation as to why the layerssometimes do not form.

3. How does the kinetic energy and distance betweenparticles compare between hot water and coldwater?

4. If you repeated this activity by trying to pour thecold water on top of the hot water, what do youthink would be the result? Explain.

5. Examine the lamp in this photograph. The heatfrom the light at the bottom of the lamp causes asolid at the bottom to turn into soft lumps of fluid.Explain why the lumps of fluids in the lamp riseand sink.

Layers of Water7-8 Find Out ACTIVITY

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Working with DensityMeasurementsDensity is an example of a property that can be used toidentify pure substances. Therefore, you could measurethe density of a pure substance to help determine itsidentity.

In the science lab, you collect all sorts ofmeasurements. Taking these measurements and turningthem into numbers that allow for analysis andcomparison is very important. In the case of density, weneed to convert a variety of mass and volumemeasurements to decimal values that make comparisonof densities easy and make it possible to identifysubstances.

Density is really a ratio of mass to volume. Forexample, a 155 mL sample of glycerol is placed on ascale and records a mass of 195 g.

(a) This would be a mass-to-volume ratio of 195 g:155 mL.

(b) This ratio can be expressed as a fraction:

(c) You can convert this fraction to a decimal bydividing the numerator by the denominator:

stto

Practice Problems

Try it yourself. First convert the following measurements into:

(a) a mass-to-volume ratio(b) a fraction(c) a decimal

To be consistent, round each of your answers to two decimal places. Thencompare your decimal values to the table in Think About It 7-6 on page 262to identify each mystery substance.

1. Mystery substance A has a mass of 1780 g and a volume of 200 cm3.What substance is it?

2. Mystery substance B has a mass of 972 g and a volume of 360 cm3.What substance is it?

3. Mystery substance C has a mass of 132.79 g and a volume of 9.8 mL.What substance is it?

4. Mystery substance D has a mass of 1404 g and a volume of 650 cm3.What substance is it?

5. Mystery substance E has a mass of 1422 g and a volume of 1800 mL.What substance is it?

Answers

1. nickel 2. aluminum 3. mercury4. salt5. ethyl alcohol


195 g155 mL

195 g155 mL

� 1.26 g/mL

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Career Connect

Diver

Q. How long have you been diving?

A. I did my first dive in a lake in Jasper about nineyears ago. Since then I have completed over3000 dives.

Q. What can divers see in the waters around British Columbia?

A. A huge number of species. British Columbia israted as the number one cold-water dive spot inthe world. The water is nutrient rich so we haveabundant marine life, such as giant pacificoctopus, sunflower stars, sea squirts, red coral,and sharks.

Q. What training do you need to become a scuba diver?

A. To get your scuba certification, you need to be at least 10 years old and complete some in-classbackground work. You learn to use the scubaequipment in a swimming pool or shallow bay.Then you do four ocean dives. To become aprofessional scuba diver, you need to doadditional diving courses and at least 100 dives.

Tony Holmes looks through the window of thesunken ship HMCS Chaudiere and sees a sea lionswim by. At 39 m below sea level, this is justanother day at work for Tony. As the owner ofSuncoast Diving in Sechelt, British Columbia, Tonyhas turned his love of the ocean and scuba divinginto a full-time business.

Q. What training do you need to dive the HMCSChaudiere?

A. You need your advanced level divingqualification to dive around the outside of theship as it is quite deep. To dive inside the ship,you need a wreck diving course. This coursefocusses on entry and exit of small places,special equipment use, carrying extra gasreserves, and special kicking techniques tominimize stirring up the silt.

Q. What science do you need to know to become aprofessional scuba diver?

A. If you want to be a divemaster, physics andphysiology are both very important. You need tounderstand buoyancy to be able to lift things tothe surface. You also need to be able to figureout the right amount of air to use, especially asthe pressure is greater and the air and waterdenser, the deeper you dive. You need tounderstand how pressure affects the body andhow gas acts on it.

Questions

1. What training do you need to become ascuba diver?

2. Why is physics important to a scuba diver?

3. What would you like most about being aprofessional diver?

Tony

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Checking Concepts1. The photograph shows six substances—oil,

corn syrup, water, plastic, Styrofoam®, and agrape—layered in a cup. Based on how theyare layered, place these six substances in a list from lowest to greatest density.

2. A balloon is filled with helium in a coldroom. The balloon is taken to a warm room where, after some time, the balloon expands.Has the density of the helium changed?Explain.

3. The picture shows that a can of diet softdrink floats in water, but a can of regular soft drink sinks. What does this tell you about therelative densities of water, the can of regular soft drink, and the can of diet soft drink?

Understanding Key Ideas4. A student measures 1080 g from a sample of

an unknown solid. If the volume of thesample is 500 cm3, what is the identity of thesolid?

5. Liquid mercury (13.55 g/mL) is denser thansolid copper (8.92 g/mL). When a drop of mercury is placed on copper, it stays on top. If mercury is denser than copper, why doesthe mercury not move down through thecopper?

If an oil spill occurs, cleaning up the oil can be a challenge. One technique is the towing of booms that contain the oil within an area.Use what you have learned about density toexplain why this technique can help clean up an oil spill.

Pause and Reflect


Soda

Soda

Reg

ular

Die

t

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Prepare Your Own SummaryIn this chapter, you investigated how the kineticmolecular theory explains the characteristics ofsolids, liquids, and gases. Create your ownsummary of the key ideas from this chapter. Youmay include graphic organizers or illustrationswith your notes. (See Science Skill 10 for helpwith using graphic organizers.) Use thefollowing headings to organize your notes:1. The Particle Model of Matter2. The Kinetic Molecular Theory3. Changing the State of Matter4. Measuring Mass, Volume, and Density5. Calculating Density

Checking Concepts1. How does the particle model explain the

difference between solids and gases?2. (a) What is kinetic energy?

(b) What happens to particles when their kinetic energy is decreased?

3. What is the difference between thermal energy and heat?

4. Describe how particles change as theychange state from (a) solid to liquid(b) gas to liquid.

5. Explain the difference betweencondensation and evaporation.

6. Why are solids denser than gases?7. How could density be used to determine

the mass of a particular volume of asubstance?

8. Fine sand can appear to flow like a fluidwhen it is dumped from a bucket. How canyou prove to someone that sand is not afluid?

Understanding Key Ideas 9. Examine the two demonstrations shown in

the following photographs. (a) A bimetallic strip has two different

metals bonded together. When heated,the strip curves. Use the kineticmolecular theory to explain the curving strip.

(b) In the ball and ring demonstration, theball is heated and then cooled. Whenhot, the ball will not fit through thering, but when it is cool, it will. Use thekinetic molecular theory to explain theball and ring demonstration.

C h a p t e r

7

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10. On a very cold day, a car enters a carwash.As soon as the hot water strikes thewindshield, it cracks. Explain this event in terms of kinetic molecular theory.

11. Nutritionists recommend limiting saturatedfats in your diet. Saturated fats, such asbutter, are solid at room temperature,while unsaturated fats, such as cooking oil,are liquid at room temperature. Whichtype of fat has the higher melting point?Explain.

12. Explain why hot water can float on top ofcold water. Use the words “density” and“particles” in your answer.

13. A student obtains a measurement of 192 gfor the mass of an 800 cm3 solid sample ofunknown material. (a) What is the density of the material?

Show your calculations, including theformula.

(b) Will the mass float on water?14. A student performs an experiment with

three unknown fluids and obtains thefollowing measurements:Fluid A: m � 2060 g, V � 2000 mLFluid B: m � 672 g, V � 850 mLFluid C: m � 990 g, V � 1100 mL(a) What are the densities of the unknown

fluids?(b) Draw how the fluids would be layered

if they were combined in a beaker.15. A 1000 cm3 sample of an unknown

substance has a mass of 917 g. (a) What is the density of the substance?(b) Would it float in water?

16. An atmospheric temperature inversionhappens when warm air settles in a layerabove cold air. When this condition occursover cities, it can create a very stable airmass that traps pollution near Earth’ssurface. Why is the air mass in atemperature inversion so stable?

17. Reinforced concrete is concrete that has had metal bars added to increase itsstrength. Without the steel, concrete cantend to be brittle and crack. Engineers are careful to use steel when reinforcingconcrete because it has almost the samerate of thermal expansion as concrete. (a) Why is it so important that the

concrete and steel have similar expansion rates?

(b) What would happen if metal bars with a different thermal expansion rate were used to reinforce concrete?

18. Describe a method by which you couldmake a substance that is more dense than water float. Explain how your methodworks.

Dissolving substances such as salt into waterincreases the density of water. Salt water hasa greater density than distilled (pure) water.Considering the formula you have learned forcalculating density, offer an explanation forwhy salt water is denser than distilled water.

Pause and Reflect

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