267

Properties of MatterIntroduction to Chapter 16

What do a silver necklace, a glass of orange juice, a helium-filled balloon, and a starhave in common? All of these objects are made of matter. In this chapter, you willlearn how matter is classified and how it undergoes changes of state. All matter canexist as a solid, liquid, or gas. Changes in temperature and atmospheric pressure cancause changes in state.

Investigations for Chapter 16

In this Investigation, you will use a technique called paper chromatography toseparate water-soluble ink (a homogeneous mixture) into its components.

In this Investigation, you will demonstrate your ability to measure the mass andvolume of liquids, and of regular and irregular solids using a variety of techniques.

In this Investigation, you will attempt to influence the rate at which 15 milliliters ofwater changes from solid to liquid. Next, you will measure the average kineticenergy of water molecules as they undergo a change of state and analyze the transferof energy that occurred.

16.1 Classifying Matter How can a homogeneous mixture beseparated?

16.2 Measuring Matter How is matter measured?

16.3 States of Matter How fast can you melt an ice cube?

Chapter 16What isMatter?

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Chapter 16: What is Matter?

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Learning Goals

In this chapter, you will:

Classify samples of matter from everyday life as heterogeneous mixtures, homogeneous mixtures, compounds, or elements.

Measure volume using the displacement technique.

Measure mass with scales and balances.

Use an indirect technique to infer mass from density measurements.

Identify the states of matter.

Classify the states of matter in order of energy.

Recognize changes in state as a physical change in matter.

Explain the states of matter in terms of molecular motion.

Identify and investigate the law of conservation of mass.

Vocabulary

atom heterogeneous mixture matter substancescompounds homogeneous mixture mixtureselements law of conservation of mass molecule

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16.1 Classifying Matter

Figure 16.1: Carbonated soft drinks are homogeneous mixtures.

Figure 16.2: Chicken noodle soup is a heterogeneous mixture.

16.1 Classifying MatterWhat is matter? Matter is easier to describe than to define. Your book, your desk, your lunch, the airthat you breathe and the water you drink are all made of matter. Matter is a term used to describeanything that has mass and takes up space. Different kinds of matter have different characteristics, suchas boiling and melting temperatures, hardness, and elasticity. In this section, you will learn how matteris classified. By the end of the section, you should be able to define mixture, homogeneous mixture,heterogeneous mixture, substance, element, and compound.

How do scientists classify matter?

Mixtures containmore than onekind of matter

Matter can be divided into two categories: mixtures and substances. Mixturescontain more than one kind of matter. For example, cola is a mixture that can beseparated into carbonated water, corn syrup, caramel color, phosphoric acid,natural flavors, and caffeine.

Homogeneousmixture isthe same

throughout

A homogeneous mixture is the same throughout. In other words, all samples of ahomogeneous mixture are the same. For example, an unopened can of cola is ahomogeneous mixture. The cola in the top of the unopened bottle is the same asthe cola at the bottom. Once you open the can, however, carbon dioxide willescape from the cola making the first sip a little different from your last sip. Brassis another example of a homogeneous mixture. It is made of 70 percent copper and30 percent zinc. If you cut a brass candlestick into ten pieces, each piece wouldcontain the same percentage of copper and zinc.

Two samples of aheterogeneous

mixture could bedifferent

A heterogeneous mixture is one in which different samples are not necessarilymade up of exactly the same proportions of matter. One common heterogeneousmixture is chicken noodle soup: One spoonful might contain broth, noodles, andchicken, while another contains only broth.

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Mixtures can beseparated by

physical means

All mixtures, whether homogeneous or heterogeneous, share one commonproperty: They can be separated into different types of matter by physical meanssuch as sorting, filtering, heating, or cooling. Chicken noodle soup, for example,could be separated into its components by using strainers and filters of differentsizes. The separation process does not change the characteristics of eachcomponent. You still have broth, noodles, and chicken.

Substances cannotbe separated byphysical means

Substances, on the other hand, cannot be separated into different kinds of matterby physical means such as sorting, filtering, heating, or cooling. Some substances,like silver, contain only one kind of matter. These substances are called elements.Other substances contain more than one kind of matter, but the different kindscannot be separated without changing the substance. For example, table salt ismade up of two elements, sodium and chlorine. If you could separate table saltinto its two elements, you would no longer have a crystallized substance that yousprinkle onto french fries and other foods. Instead, you would have sodium, a softmetal that can cause an explosion if dropped into water, and chlorine, a yellowish,poisonous gas.

All substances areeither elements or

compounds

Table salt and other substances that are made of two or more elements that cannotbe separated by physical means are called compounds.

Figure 16.3: Sodium, a soft metal, and chlorine, a toxic gas, react to form the very edible and useful compound table salt (NaCl).

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16.1 Classifying Matter

�Petroleum is a heterogeneous mixture

Petroleum is a very old andcomplex mixture that weextract from the Earth.Formed millions of yearsago, petroleum contains100,000 to 1,000,000different molecules! A usehas been found for just aboutevery component of thisheterogeneous mixture.Important petroleumproducts include fuel, oils,asphalt, and waxes. Refiningpetroleum is a process that isused to separate the specificcomponents to make eachproduct. Refining includesphysical processes (likedistillation) and chemicalreactions to isolate thecomponents of petroleum.

How can youseparate mixturesinto substances?

Separating mixtures into substances is a very important part of scientific work.Medical researchers try to isolate the substances in plants that may help healdiseases. Forensic scientists try to match evidence from the scene of a crime withsubstances found with a suspect. Nutritionists evaluate the amount ofcarbohydrates, fats, proteins, vitamins, and minerals in various foods.

Separating mixtures is not always an easy task. In this unit you will learn about avariety of physical properties that can be used to identify substances in a mixture.Later, you will learn how chemists work to break down substances even further, sothat they can separate compounds into elements.

Table 16.1: Summary of the types of matter

Type of matter Definition Examples

Homogeneous mixture A mixture that contains more than one type of matter and is the same

throughout.

soda pop, air, chocolate ice cream

Heterogeneous mixture A mixture that contains more than one type of

matter and is not the same throughout.

chicken soup, soil, fudge ripple ice cream

Element A substance that contains only one type of atom.

copper metal, oxygen gas, liquid nitrogen

Compound A substance that contains more than one type of

atom.

table salt, rust (iron oxide), carbon dioxide gas

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Figure 16.4: The meniscus of water curves downward. Read the mark at the bottom of the curve.

Figure 16.5: The meniscus of mercury curves upward. Read the mark at the top of the curve.

16.2 Measuring MatterHow many gallons of gasoline do I need to fill the tank of this car? Do I have enough sugar to make abatch of brownies? Will this suitcase fit in the airplane’s overhead compartment? Every day, peopleneed to measure various amounts of matter. In this section, you will review how to measure the massand volume of matter, and become proficient at using the displacement method to find the volume ofirregular objects.

Measuring volume and mass

Read volumemarks at eye level

for accuracy

Measuring the volume of liquid matter is easy. You simply pour it into a markedcontainer such as a measuring cup, graduated cylinder, or beaker, and read thevolume mark. To get the greatest accuracy, there are two things to keep in mind.First, read the mark at eye level. Second, you may notice that the surface of theliquid forms a curve (like a hill or a valley), rather than a straight line. This curveis called the meniscus. If the surface curves downward, (liquid water does this)read the volume at the bottom of the curve. A few liquids, like mercury, will forman upward curve. In this case, read the volume mark at the top of the curve.

You can calculatethe volume ofsolids using a

formula

You have probably already learned to measure the volume of some solid shapes.The volume of a rectangular solid (a shoebox shape), for example, is found bymultiplying length times width times height. Some common volume formulas areshown in table 16.2.

Table 16.2: Volume Formulas

Shape Formula in words Formula in symbolsrectangular solid and

cube length × width × height l × w × h

cylinder pi ×radius2 × height πr2 × hcone 1/3 × pi × radius2 × height 1/3 × πr2 × h

sphere 4/3 × pi × radius3 4/3 × πr3

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16.2 Measuring Matter

The displacementmethod

We can find the volume of an irregular shape using a technique calleddisplacement. To displace means to “take the place of” or to “push aside.” You canfind the volume of an irregularly shaped object by submerging it in water andmeasuring how much water the object displaces or pushes aside.

How you makethe measurement

You can use this method to find the volume of an ordinary item like a house key.Fill a 100-milliliter graduated cylinder with 50 milliliters of water (figure 16.6).Gently slide the key into the water. The water level in the container will rise,because the key displaced, or pushed aside, some water. If the level now reads53.0 milliliters, you know that the key displaced 3.0 milliliters of water. Thevolume of the key, or of any object you measured in this way, is equal to thevolume of the water it displaced. The key has a volume of 3.0 milliliters, or 3.0cubic centimeters (cm3).

Mass is theamount of matter

in an object

Sometimes we are more concerned about the quantity of matter we have, ratherthan the space it takes up. Breakfast cereal, for example, isn’t sold by volume. Asboxes of cereal are shipped from plant to warehouse to store, the contents “settle.”By the time the cereal is purchased by the consumer, the container may appearonly three-fourths full. For this reason, cereal is measured in grams. An equalmass of cereal is placed into each container at the factory.

How does a scalework?

A scale measures the gravitational force between an object and Earth. This meansthat a scale that reads in grams or kilograms has actually measured weight andcalculated the mass from the weight.

How does abalance work?

A balance measures the mass of an object (likea quantity of cereal) by comparing it withobjects whose masses are known. Since abalance measures by comparing standardmasses, it is not affected by changes in gravity.

Would a balance function correctly on themoon? Why or why not?

Figure 16.6: The key displaced 3.0 milliliters of water.

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Figure 16.7: When the old tennis court asphalt is removed, a child’s playground can be built in its place.

Measuring very large or very small quantities of matter

How could you measure a quantity of matter that is too large for a balance ordisplacement tank? Read on to find out how a citizen’s group solved this problem.

How could youmeasure the mass

of an asphalttennis court?

After years of watching a tennis court fall into disrepair at a local park, a group ofneighbors got together to discuss what could be done with the site. They voted toapproach the town council to see if a children’s play structure could be built there.The town council asked the group to provide a budget for the renovation. It waseasy for the group to find prices for new play structures; but first, the tennis courtwould have to be taken down and the asphalt removed. The group learned that thefee for disposing of construction or demolition debris was 5 cents per kilogram.How did they figure out the cost of asphalt disposal?

Indirectmeasurement

The group used a technique called indirect measurement to estimate the disposalcost. First, they picked up a palm-sized chunk of loose asphalt from the tenniscourt. They used displacement to find its volume: 1,687 cubic centimeters. Usinga balance, they found that the chunk had a mass of 1.94 kilograms.Next, they measured the tennis court: 36.51 meters by 18.29 meters. Theyestimated the asphalt to be 0.075 meters thick. By multiplying length × width ×depth, they found that the court contained 50.08 cubic meters of asphalt.

Set up aproportion

Now they could set up a proportion:

The volume of the chunk was converted to cubic meters so that the units wouldmatch. The group solved their equation for the mass of the court, and found thatthe asphalt had a mass of 57,590.5 kilograms.At 5 cents per kilogram, the disposal fee came to $2,879.52.

How to measurevery small objects

Indirect measurement can also be used to measure very small quantities. If you putone sunflower seed on a balance, the balance still reads 0.0 grams. This means thatthe mass of the seed is less than 0.1 gram! It might be 0.04 grams or 0.00964grams, but how could you find out? Use indirect measurement by finding the massof 100 sunflower seeds and then dividing it by 100.

mass of chunk

volume of chunk------------------------------------

mass of court

volume of court-----------------------------------=

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16.3 States of Matter

Figure 16.8: A single crystal of sodium chloride (table salt) is a cube. The molecules are arranged in the crystal so that each sodium atom is surrounded by six chlorine atoms, and six sodium atoms surround each chlorine atom.

16.3 States of MatterSuppose your teacher gave each student a teaspoon of salt and offered a reward to the person who couldseparate out the smallest piece. How would you do it? You might start by sprinkling a few grains onto apiece of dark paper. Perhaps you could isolate one grain. Next, you might try to smash that grain intosmaller particles with a hammer. If you were able finally to divide the grain of salt into particles assmall as a speck of dust, you might have won the contest, but your bit of salt would still be about 100 trillion times as large as the smallest possible piece! In this section, you will learn about thesmallest whole particles of matter, atoms and molecules. By the end of the section, you should be ableto describe how those particles move in solids, liquids, and gases.

Atoms and molecules

Molecules andatoms

Scientists call the smallest possible particle of a compound that retains theproperties of the compound a molecule. The smallest possible particle of anelement is called an atom. Atoms and molecules are more than a trillion timessmaller than a human cell, a bacterium, and everything else that can be seen withan optical microscope. We know they exist because we can describe and predicthow they will act in various substances and mixtures.

Movement ofmolecules

Let’s examine a very common compound, water. Water is one of the mostimportant substances on the planet. It covers more than 70 percent of the Earth’ssurface. Without it, life would not be possible. We need water for our bodies tofunction properly and for plants to grow. We use ice to preserve food. Steam-powered turbines and hydroelectric dams provide electricity for homes andbusinesses.

Atoms andmolecules are

always in motion

Each tiny water molecule contains one oxygen atom and two hydrogen atoms. Asingle drop of water is made up of more than 3 x 1021 molecules. These moleculesare always in motion. At higher temperatures, they move faster and bump into oneanother with more force. At lower temperatures, they move with less energy.

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Changes of state

Molecules insolids, liquids and

gases vibratedifferently

At temperatures below 0°C, water is a solid called ice. In the solid state, moleculesconstantly vibrate, but cannot switch places with other molecules. Between zeroand 100°C, water is a liquid. Molecules in a liquid move faster and slip out ofposition. Liquids flow because the molecules can move. At temperatures above100°C, water becomes a gas. At this high temperature molecules move so fast thatthey bounce out of the liquid state and become a gas. In the gaseous state,molecules are widely separated.

What istemperature?

Temperature influences changes of state. Temperature measures the averageenergy of a certain amount of molecules, and is related to the average velocity ofthe molecules. The higher the temperature, the faster (on average) the moleculesmove.

Melting andboiling

The temperature at which the water changed from solid to liquid is called itsmelting point. The temperature at which it changed from liquid to gas is called theboiling point. Different substances change from solid to liquid and from liquid togas at different temperatures. Iron, for example, melts at 1538°C (2800°F) andboils at 2861°C (5182 °F). These changes are called changes of state.

What isevaporation?

Fast-moving molecules in a liquid can escape to become a gas. The wordevaporation describes the transformation from the liquid to gas. Evaporation is acooling process. For example, when you step out of a shower, you often feel cold.The reason is that when water evaporates from the surface of your skin, thehighest energy molecules are the ones that jump from liquid to gas. Lower energymolecules are left behind. The high energy molecules that leave take away energyso your body feels cooler!

What iscondensation?

The evaporation of water is an important part of the Earth’s water cycle (alsocalled the hydrologic cycle). Water in the oceans, lakes, ponds, and rivers becomespart of the Earth’s atmosphere when it evaporates. Once water vapor is part of theatmosphere, some molecules will collect to form small droplets. Clouds are largeformations of water droplets. The process of transforming from a gas to a liquid iscalled condensation. When water droplets in a cloud get too big, they fall back tothe Earth as rain.

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16.3 States of Matter

Figure 16.9: Steel nails are an example of a solid.

Figure 16.10: Liquids flow to take the shape of the container but keep their volume.

Figure 16.11: A gas expands to fill its container, such as a balloon.

A solid cansometimes changedirectly into a gas

Have you ever noticed that ice cubes sometimes seem to shrink when they havebeen in the freezer for a long period of time? Sometimes a solid can changedirectly to a gas when heat energy is added. This process is called sublimation.Solid iodine is a substance that readily undergoes sublimation at roomtemperature. This is evident by a the formation of a purple cloud above thecrystals.

States of matter

All substances canexist as a solid,

liquid, or gas

On Earth, elements and compounds are usually found as solids, liquids, or gases.These are called states of matter. Each substance can exist in each of the threestates, and each substance has a characteristic temperature and pressure at which itwill undergo a change of state.

A solid retains itsshape and size

Although we cannot easily see the molecules of a substance moving around, wecan describe the resulting characteristics of the matter in each state. When asubstance is in a solid state, the molecules vibrate, but they cannot changeposition. As a result, a solid retains its shape and size. For example, steel nails donot change shape so that you can fit more in a jar (figure 16.9).

A liquid hasdefinite size,but not shape

In the liquid state, molecules of a substance can move over and around each other.Therefore, the liquid has a definite volume, but no definite shape. Instead, it willtake on the shape of whatever container it is poured into (figure 16.10).

Table 16.3: Changes of state at 1 atm (normal atmospheric pressure)

Substance Melting/freezing point Boiling/condensing point

helium -272°C -269°Coxygen -218°C -183°Cmercury -39°C 357°C

water 0°C 100°Clead 327°C 1749°C

aluminum 660°C 2519°C

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A gas hasno definite shape

or size

In the gas state, molecules move around freely and separate from one another. Inthis state, a substance has neither a definite size nor shape. It will spread outevenly throughout its container.

Change of stateand mass

When a substance undergoes a change of state, only the movement of themolecules changes. The number of molecules does not change. The mass of thesubstance remains the same whether it is in the solid, liquid, or gas state.

Plasma is a fourthstate of matter

The most common state of matter in the universe is a state rarely found on Earth:plasma. Matter enters the plasma state when it is heated to such a high temperaturethat some of the atoms actually begin to break apart. They lose their outer layer ofelectrons. For most materials this requires temperatures of more than 10,000 degrees.

Where do you findplasma?

Our sun and other stars are made of plasma. Scientists believe the core of the sunhas a temperature of about 15 million degrees. The surface of the sun is about5,000 degrees. A type of plasma is used on Earth to make neon and fluorescentlights. Instead of heating the gases to an extremely high temperature, an electricalcurrent is passed through them. The current strips the electrons off the atoms,producing plasma. You also see a plasma every time you see lighting.

The four familiarstates of matter

Matter has four states that we experience. In order of increasing energy they are:solid, liquid, gas, and plasma. Since temperature is a measure of energy, matterchanges from one phase to another as its temperature is increased.

Exotic super-hotstates of matter

If an atom of a substance keeps getting hotter, eventually even the nucleus of theatom comes apart. Some very exotic states of matter exist in particle acceleratorsthat heat matter up to trillions of degrees and more.

�High-altitude cooking

Did you know that thefreezing and boiling points ofa substance change as the airpressure changes? At a lowerair pressure, it is easier forwater molecules to escapefrom liquid into the air.Therefore, water will boil ata lower temperature. This iswhy cake mixes often havehigh-altitude directions. Thelower air pressure at highaltitudes allows the water inthe mix to begin to turn togas at a lower temperature,so it begins to leave themixture earlier. To preventthe cake from drying out,extra water is added to themix and the oven is set to alower temperature.

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Chapter 16 Review

Chapter 16 Review

Vocabulary Review

Match the following terms with the correct definition. There is one extra definition in the list that will not match any of the terms.

Concept review

1. What are the two major categories of matter?

2. Name three foods that would be classified as heterogeneousmixtures, and three foods that are homogeneous mixtures.

3. Explain the difference between the two kinds of substances.

4. Explain the difference between an atom and a molecule.

5. Describe the movement of atoms or molecules in solid form.

6. Describe the movement of atoms or molecules in liquid form.

7. Describe the movement of atoms or molecules in gas form.

8. A liquid takes the shape of its container, but why doesn’t aliquid expand to fill the container completely?

9. List at least two similarities between mass and volume and atleast two differences.

10. Evaporation and boiling can be referred to at the same time asvaporization. Describe the difference between vaporization andsublimation.

Set One Set Two1. matter a. Two samples of this material might contain

different kinds of matter1. substance a. Very tiny; microscopic

2. homogeneous mixture b. A pure substance which contains only one kind of matter

2. mixture b. Calculating size of very large or small objects through use of proportional relationships

3. heterogeneous mixture c. Any material that contains at least two kinds of matter

3. meniscus c. Measuring volume by placing an object in water and recording the change in water level

4. element d. Anything that has mass and takes up space 4. displacement d. The curve formed by the surface of a liquid

5. compound e. Contains two or more kinds of matter that cannot be separated by physical means

5. indirect measurement e. A sample of matter that cannot be separated by physical means; may contain only one or several kinds of matter

f. Every sample of this material is the same f. A sample of matter that contains two or more kinds of particles that can be separated by physical means

Chapter 16 Review

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Problems

1. How could you use indirect measurement to find the mass of alarge boulder?

2. How could you use indirect measurement to calculate thethickness of one index card?

3. As you know, the Earth is a watery planet. About 70 percent ofthe Earth’s surface is covered by water. There is waterunderground, and even in the atomosphere. What is water’sstate at each of the following temperatures?a. temperatures below zero degrees Celsiusb. temperatures between zero and 100 degrees Celsiusc. temperatures above 100 degrees Celsius

�Applying your knowledge

1. Design a poster to illustrate the classification of matter.Provide examples of everyday objects that belong in eachcategory.

2. Construct a three-dimensional model that could be used in afourth-grade classroom to explain how molecules move in thesolid, liquid, and gaseous states.

3. �Land surveyors measure and map land. One of their jobs isto figure out the dimensions of land features and formations.Interview a surveyor to learn how indirect measurement is usedto calculate precise distances. Prepare a five-minute report foryour class.

4. Look around your classroom or home and name an object thathas a relatively large mass, but has a relatively small volume.Name an object that has a relatively small mass, but has arelatively large volume.

5. Write a brief procedure for determining:a. the volume of a rock; andb. the mass of a small amount of orange juice.

6. How could you determine the percentage of empty space in asquare cleaning sponge?

7. Design a poster or model to summarize for your classmates thedifference between a solid, liquid, gas, and plasma.

8. Create a chart that illustrates the state changes: melting,boiling, freezing, evaporation, condensation, and sublimation.

9. Plasmas, or ionized gases as they are sometimes called, are ofgreat interest both physically and technologically. Do someresearch to find out why plasmas are of great interest toscientists and manufacturers. Describe at least two current usesof plasmas, and describe one way scientists and engineers hopeto use plasmas in the future.