Chapter 8 Density PDF

S tanding in the basket, you look up at the giant balloon above you. It seems impossible that you will ever get off the ground. The pilot beside you reaches up and pulls on the burner, sending a hissing flame and heat into...

S tanding in the basket, you look up at the giant balloon above you. It seems impossible that you will ever get off the ground. The pilot beside you reaches up and pulls on the burner, sending a hissing flame and heat into the balloon. Suddenly, and quietly, you are lifted off the ground. It feels as though Earth is being pulled away from you, even though you are the one who is quietly moving, drifting upward as you are guided by the wind. Without jet engines and propellers how do these hot-air balloons float upward? The answer has to do with the density of the air inside the balloon. In this chapter, you will learn about the property of density and how it is unique to each individual substance. You will also explore how density helps to explain how certain substances interact with one another. 300 MHR Unit 3 Fluids NL8 U2 CH08.indd 300 11/5/08 3:43:57 PM  FOLDABLES TM Reading & Study Skills Make the following Foldable to take notes on what you will learn in Chapter 8. What You Will Learn STEP 1 Fold a vertical sheet of legal-size paper from left In this chapter, you will to right two times. Unfold. Describe the difference between mass, volume, and density Explain the relationship between mass, volume, and density using the particle theory STEP 2 Fold the paper in half from Predict how temperature will affect the top to bottom two times. density of a substance Why It Is Important STEP 3 Unfold and draw lines along the folds. Density is a property that can help identify a specific substance. Understanding density can also help us understand the way things work around us. STEP 4 Label the top row and first columns as shown below. Skills You Will Use Define + Heat – Heat States Liquid In this chapter, you will Water Determine mass-to-volume ratios of Water as a Gas different amounts of the same substance Water as a Measure density of fluids and solids Solid (Ice) Observe how temperature and density affect our everyday lives Read and Write As you read the chapter, define the states of matter in the Define States column of your Foldable. Write what happens when heat is added to or lost from each state. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 301 NL8 U2 CH08.indd 301 11/5/08 3:44:07 PM  8.1 Defining Density 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. Key Terms One property that is useful in understanding both fluids and solids is density. Density is the amount of mass in a certain unit density volume of a substance. In other words, density describes how closely packed together the particles are in a material. You might think of density in terms of vehicles on a highway. A traffic jam like the one on the left in Figure 8.1A is a model of high density. The photograph of free-flowing loosely packed traffic on the right in Figure 8.1B is a model of low density. Figure 8.1(A) When traffic gets very dense, it is difficult for vehicles to move. (B) When the density of traffic is lower, cars can move more easily. Word Connect Density and the Particle Theory According to the particle theory, different substances have The word density comes different-sized particles. The size, shape, and mass of the from the Latin word densus, particles determine how many particles and how much mass can meaning "thick or crowded". “fit into” a given space. Therefore, each substance has its own unique density, based on particle size, shape, and mass. The particle theory also suggests that there is empty space between the particles of matter. If you look back at Figure 8.1B, you can see that not as many cars can fit on the highway if there are large spaces surrounding each vehicle. The density of the traffic is reduced. Therefore, the more space that exists between particles of a substance in a certain unit of volume, the less dense the substance will be. 302 MHR Unit 3 Fluids NL8 U2 CH08.indd 302 11/5/08 3:44:12 PM  Density of Solids, Liquids, and Gases How is the density of a substance related to the substance’s physical state? Imagine filling a container with liquid water and Did You Know? another container of the same size with water vapour. Both Could the solid state be less dense liquid water and water vapour are the same substance, and than the liquid state of the same therefore have particles of the same size and mass. According substance? The answer is yes for some substances. You have to the particle theory, however, gas particles have more space probably seen ice cubes floating in between them than do liquid particles. Therefore, the water a glass of water. As solid ice forms vapour in the container would have fewer particles than the from liquid water, the ice expands. liquid water. You can then conclude that the density of the water This means that there is more vapour is less than the density of liquid water. empty space trapped in a chunk How are density and state of matter related to the physical of ice than in the same amount of properties of a substance? Solid objects can move easily through water. Therefore, solid ice is less dense than liquid water. liquids and gases. For example, a diver can jump from a platform and move smoothly through the air and then the water in a pool, as shown in Figure 8.2. According to the particle theory, the fluid properties of water and of air allow water particles and air particles to move out of the way of the solid body of the diver. Why do solid particles tend to hold together while fluid particles tend to move apart? The answer has to do with the attractive forces between particles. In solids, particles cannot be easily pushed apart. To understand why, imagine that you and a few friends are together. You want to prevent anyone else from pushing your group apart and moving between you. What would you do? First, you would have to stand quite close together. Then, you would probably hold on to each other very tightly. If you do not let go of one another, no one can move between you. Particles in a solid act much the same way. Attractive forces among the particles of a solid are stronger than those between fluid particles. Therefore, particles in a solid cannot slide past each other or move between each other. Figure 8.2 The particles of a If you were to place a fluid move apart easily when a rock on the surface of a solid object, such as a diver, travels lake, the water would not through the fluid. support the rock. Instead, the rock would go right through the water, and would continue to Figure 8.3 The cartoon fall through the water, weightlifters represent the tightly pushing water particles packed particles of the solid plate. The plate can hold its shape and out of its way until it support materials such as the large reached the bottom. rock because the weight-lifters (plate Liquids cannot support particles) are holding on to each other very tightly. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 303 NL8 U2 CH08.indd 303 11/5/08 3:44:13 PM  objects in the same way that solids can, because the particles of a liquid move apart easily, allowing a dense, solid object, such as a rock, to pass through the liquid. The attractive forces between Did You Know? liquid particles are not strong enough to prevent a rock from “Empty space” does not mean pushing them apart. “air.” Empty space means a Similarly, a rock falls through air because gases are even less separation between two objects dense than solids or liquids. When you move through air, you with nothing between those objects, not even air particles. are moving through mostly empty space. A solid object does not Simply because empty space have to move as many particles of air out of the way as it would and air look the same does not travelling through water. This explains why running through air mean they are the same! For is much easier and faster than running through water. In general, example, outer space is mostly gases are less dense than liquids and liquids are less dense than empty space, but it has no air. solids. Astronauts would suffocate if they were to venture outside their spacecraft without masks and air tanks, because there is no oxygen in outer space. Figure 8.4 Although liquid particles are sometimes quite Figure 8.5 When a solid object moves through air, it closely packed together, they cannot support objects in does not have to move as many particles of air out of the same way that solids can, because the particles do not the way as it would when passing through a liquid, since have a strong enough attraction for each other. Therefore, gases are usually less dense than liquids. Gas particles are liquid particles move apart easily. even less attracted to each other than particles in liquid. 304 MHR Unit 3 Fluids NL8 U2 CH08.indd 304 11/5/08 3:44:23 PM  8-1A Differing Densities Find Out ACTIVITY Using your knowledge of the particle theory, what 2. With a partner, pick up each container and inferences can you make about the densities of observe how heavy or how light each one feels. different substances? Decide on the order of the containers from heaviest to lightest. Give the heaviest container Safety rank number 5 and the lightest container rank number 1. In your table, record the ranks of the containers, from heaviest to lightest. 3. Predict what the substance inside each container What You Need might be. Record your predictions. 3–5 class sets of lettered containers (prepared by 4. Find out what the substances are by checking your teacher), filled to the brim with various “mystery your teacher’s master list. Record the actual substances” substances in the table. What Did You Find Out? 1. Which substances did you predict correctly (or closely)? Which substances, if any, surprised you? 2. The volumes of the substances were identical because each container was filled to the top. Why is it important to keep the volumes equal in this activity? What to Do 1. Make a table with the following headings: Sample Rank Substance (letter) (ordered heaviest to lightest) Your prediction Actual Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 305 NL8 U2 CH08.indd 305 11/5/08 3:44:25 PM  In some cases, the densities of two pure substances can be so different that the liquid state of one is denser than the solid state of the other. One example of this is shown in Figure 8.6A. Many solid metals, such as copper, nickel, and silver, can float on liquid mercury, one of the densest substances known. Another example of water being denser than a solid is shown in Figure 8.6B. Figure 8.6A Liquid mercury is so dense that it can support a solid Figure 8.6B A solid block of wood floats easily on the iron bolt. A layer of oil has been placed on top of the mercury to surface of liquid water. prevent vapour from escaping into the surrounding air, as mercury is very poisonous. Reading Check 1. Explain what density means in your own words. 2. Explain why solids can support objects more easily than fluids can. You may use diagrams to help in your explanation. 3. How can the density of a pure substance change? Provide an example. 4. Using the particle theory, explain why some liquids can support a solid. 306 MHR Unit 3 Fluids NL8 U2 CH08.indd 306 11/5/08 3:44:28 PM  The Mercury Barometer Vacuum Glass tube If you watch a weather forecast, you will often hear the meteorologist talk about high or low pressure systems. Our weather changes as systems Height Mercury of high and low atmospheric pressure are carried 76 cm column by winds and move over the land. Atmospheric pressure is measured by an instrument called Air Air pressure pressure a barometer. Although digital and other types of barometers now exist, the original and most common barometers work because of the unique Mercury properties of liquid mercury. in dish Why Use Mercury? You may wonder why water was not used in these original barometers. The answer has to do with the high density of mercury. For a column of water to create as much pressure as the standard atmospheric pressure (101.325 kPa), it would have to be 10 m high. That would not be very practical, as you would have to have a glass tube that was over 10 m in height! Because mercury is much denser than water, but is still a liquid, it only takes 76 cm of mercury to make a column that exerts Mercury is a dense metal that is liquid at room temperature. one atmosphere of pressure. In 1643, Evangelista Torricelli developed the first mercury barometer, and it has changed very The End of the Mercury Barometer? little in design since then. The air is removed from There are some very important problems with a glass tube (about 76 cm in length) that has one mercury that could mean that mercury barometers closed end and one open end. The open end is will stop being made. Scientists discovered that then placed into a reservoir of liquid mercury. As liquid mercury is highly toxic to humans and atmospheric pressure increses, it presses down animals. Many countries have banned the use of on the reservoir and forces the mercury up into mercury in manufacturing industries in order to the tube. The mercury rises until the weight of prevent it from entering the environment. the mercury in the tube balances the atmospheric force that is exerted on the reservoir. The higher the pressure, the higher the mercury will rise in the tube. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 307 NL8 U2 CH08.indd 307 11/5/08 3:44:30 PM  Icebergs giants can float at all! Icebergs Each spring, tourists and residents of Newfoundland float because the and Labrador alike gather along the shores to density of ice is watch white, silent giants slowly drift past in the approximately ocean. The sheer size of these ancient icebergs 0.9 g/mL, which boggles the mind, is lower than especially when we that of seawater know we are only It is hard to imagine that 90 percent of Iceberg Alley (around this giant is hidden from view underneath seeing “the tip of the 1.03 g/mL). the water. iceberg.” The area from the northern Iceberg Lingo tip of Labrador down Iceberg scientists and enthusiasts use words that a to the Grand Banks tourist might find strange! of Newfoundland is “growler” – very small chunk of floating ice that called Iceberg Alley. It rises only about one metre out of the water is through this alley “bergy bits” – small icebergs that rise one to that many icebergs four metres out of the water flow from the Arctic on Iceberg Alley is known as one of “calving” – when part of an iceberg splits away their journey to warmer the best places in the world to see icebergs. and falls into the ocean waters. “tabular,” “wedged,” “pinnacled,” “domed,” Where do the Icebergs in Iceberg Alley “blocky,” and “drydocked” – shapes of icebergs come from? The icebergs were originally part of Greenland’s Global Warming—The End of Icebergs? glaciers. Breaking off from one of the glacier’s Since the late 1990s, there has been a decline in the edges, an iceberg is caught in the Labrador Current number of icebergs that pass through Iceberg Alley. and is carried into the alley along the shores of Many scientists believe that this decline has to do Labrador and then Newfoundland. But do not be with global warming—the increase in the average tricked into thinking that this is a quick journey. It temperature of the Earth’s near-surface air and takes an iceberg about two to three years to reach oceans. As the air and ocean temperature increases the Grand Banks of Newfoundland from Greenland! even a few degrees, more icebergs are created from Greenland’s glaciers, but they are melting before The “Tip of the Iceberg” they reach Iceberg Alley. A lack of icebergs is good You have probably heard the saying that 90 per news for ships that pass through the alley and for cent of an iceberg remains below the surface of the oil rigs such as the Hibernia. However, it is bad water. Considering that the average weight of an news for tourists who come to see the icebergs, iceberg off the Grand Banks is one to two hundred and for the province that enjoys the benefits of the thousand tonnes, it is hard to believe that these tourism industry. The decline could also possibly be a warning for the future of Earth’s environment. 308 MHR Unit 3 Fluids NL8 U2 CH08.indd 308 11/5/08 3:44:34 PM  Checking Concepts Understanding Key Ideas 1. Imagine that you have two equal-sized 6. Explain why “air” and “empty space” are containers. One is filled with liquid gold, two different things. and the other is filled with solid gold. 7. Many people take water aerobics classes Using the particle theory, explain why because it is a good physical activity to each physical state of gold will have a stay in shape. Why would doing some different density, despite the fact that exercises, such as running through water, they are both gold. be harder than doing it through the air? 2. Using the particle theory, explain why dolphins can move easily through the air and the ocean when they jump. Pause and Reflect 3. Find some small items in the classroom (for example, pencils or paper clips) and determine whether these items are denser than water by dropping them into a container full of water. Organize your observations in a table. 4. The density of molten lava increases as it cools and hardens. List other examples of If an oil spill occurs, cleaning up the oil natural changes in density. can be a challenge. One technique is the 5. Explain why the attractive forces of towing of booms that contain the oil within particles make the densities of solids, an area. Use what you have learned about density to explain why this technique can liquids, and gases so different? help clean up an oil spill. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 309 NL8 U2 CH08.indd 309 11/5/08 3:44:39 PM  8.2 Determining Density How can you measure the density of a substance? You can determine a substance's density if you know how much of a substance occupies a certain space. Key Terms Recall that density is the mass of a given volume. To find the density of a substance, you need to know its mass and its displacement volume. Mass is the amount of matter in a substance (see Figure mass 8.7). Volume is a measurement of the amount of space occupied mass-to-volume ratio by the substance. Figure 8.8 shows how the volume of a solid volume can be measured. The volume of a liquid can be measured using a measuring cup or a graduated cylinder. The volume of a gas can be determined by measuring the volume of the container that holds it. Figure 8.7 A balance is used to measure mass in grams (g) or kilograms (kg). This apple has a mass of 102 g. Figure 8.8 If an object has a regular shape, such as the block of wood in this picture, you can measure the length, width, and height and then use the mathematical formula, V = l × w × h, to calculate the object’s volume. Displacement How would you measure the volume of an object with an irregular shape? Displacement is the amount of space that an object takes up when placed in a fluid. Have you ever noticed how the water level Figure 8.9 The volume of an irregularly shaped object rises in a bathtub when you get into it? The amount can be found by measuring the volume of the water that spills out of an overflow can. of water you are displacing is the volume of your body that is in the water. So, by measuring the Suggested Activity displacement of an object, you can measure the Conduct an Investigation volume of the object. 8-2A on page 315. 310 MHR Unit 3 Fluids NL8 U2 CH08.indd 310 11/5/08 3:44:40 PM  Calculating Density The density of a substance can be determined by calculating its Did You Know? mass-to-volume ratio. You can do this by dividing the object’s mass by its volume. Therefore, the formula for density is: Forensic scientists use density calculations to solve crimes! The Mass (m) ​ m ​ Density (D) = ​ _________​or simply, D = __ density of glass fragments found Volume (V) V at a crime scene or on a suspect’s The volume of a solid is often given in units of cm3. Therefore, clothing can be compared to the density of other samples of the density of solids is often given in g/cm3. The volume of glass. This may provide evidence liquids, however, is often given millilitres (mL). Therefore, the that a particular suspect was density of liquids is often given in units of g/mL. present at the crime scene. What information would scientists need to calculate the density of the glass fragments? How might they gather this information? A Figure 8.10A The salt and sugar shown here both have a mass of B 0.5 kg and are the same colour. However, their densities are different. Seawater may look like regular water (B) , but its density is closer to that of milk—1.03 g/mL. As long as the temperature and pressure stay the same, the mass-to-volume ratio, or density, of any pure substance is a constant, meaning it does not change. If the mass of a pure substance increases, the volume will also increase. Similarly, if the volume of a pure substance increases, the mass will also increase. According to the particle theory, the size of the particles in Suggested Activity a substance do not change when the mass or volume of the Investigation 8-2B on substance changes. A certain number of particles of a particular page 316. size and mass will always occupy a certain amount of space. Density is a property of matter that is unique to a specific pure substance. Table 8.1 on the following page lists the approximate densities of some common substances. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 311 NL8 U2 CH08.indd 311 11/5/08 3:44:41 PM  Table 8.1 Approximate Densities of Common Fluid Substances and Solid Substances 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 Scientists determined the values in Table 8.1 by making very careful measurements of the mass and volume of samples Did You Know? of the substances and using the formula for density. Learn how You can place the density scientists make these calculations by studying the sample problem formula in a triangle graphic to below. Then, develop your problem solving skills by completing make it easier to manipulate: the practice problems that follow. m Sample Problem D V Find the density of a 10 g mass of a substance that has a volume of 2.0 cm3. By using your thumb to cover up Write the formula for density. ​ m ​ D = __ the variable for which you wish V to solve, you will be able to see 10 g the formula required. In place of m for mass, write 10 g. D = ​ ____​ V If you wish to find the density 10 g (solve for D), cover up the D: In place of V for volume, write 2.0 cm3. D = ​ ______3 ​ 2.0 cm Carry out the division. m g That is, divide 10 by 2.0. D = 5.0 ___ ​  3 ​ cm D V The density of the substance is 5.0 g/cm3. The formula can be read as "m Practice Problems over V", or mass divided by volume. 1. A  piece of metal has a mass of 8.1 g and a volume of 3.0 cm3. What is the density of the metal? Look at the densities of the solids in Table 8.1. What type of metal do you think was described in this problem? 312 MHR Unit 3 Fluids NL8 U2 CH08.indd 312 11/5/08 3:44:42 PM  2. I magine that you poured a liquid into a measuring spoon that holds 2.5 mL. When you measured the mass of the liquid, you discovered that its mass was 3.15 g. What is the density of the liquid? Was this liquid water? Explain how you could check if the liquid was water. 3. Y  ou collect 1000 mL of a gas in a balloon. If the gas in the balloon has a mass of 2.0 g, what is the density of the gas? Use Table 8.1 to identify the gas. If you know the density of a substance and are given the mass of a sample of the substance, you can predict the volume of the sample. To do this, you use a different form of the formula. If Did You Know? you rearranged the formula, you would find that V = __​ m ​. Learn Use the triangle graphic technique D how to use this form of the formula by studying the sample to find the volume by covering up the V in the triangle: problem below. Then, complete the Practice Problems. Sample Problem m You want to put 10.0 g of salt into a container. What is D V the volume of the container if the salt completely fills it? The formula can be read as "m W  rite for formula for volume when ​ m ​ V = __ D over D", or mass divided by you know the mass and density. density. L  ook up the density of salt D = 2.16 g/cm3 in Table 8.1. 10.0 g In place of m for mass, put 10.0 g. V = ​ _____​ D 10.0 g I n place of D for density, V = ​ _________3 ​ 2.16 g/cm put 2.16 g/cm3. C  arry out the division. That is, divide 10.0 by 2.16. V = 4.63 cm3 The volume of 10.0 g of salt is 4.63 cm3. The container holds 4.63 cm3. Practice Problems 1. A  piece of gold has a mass of 9.66 g. What is its volume? 2. What volume is taken up by 15 g of helium? 3. W  hat is the volume of 250 g of sea water? Would the same mass of pure water have a larger volume or a smaller volume than the sea water? Explain. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 313 NL8 U2 CH08.indd 313 11/5/08 3:44:43 PM  By rearranging the formula for density in another way, you can calculate the mass of a given volume of a substance if you know Did You Know? its density. The formula for calculating mass is m = VD or mass Use the triangle graphic equals the volume times the density. Study the following sample technique to find the mass problem, and then complete the practice problems. (solve for m) by covering up the m in the triangle. Sample Problem What is the mass of 1500 mL of helium? m W  rite the formula for m = VD mass when you know D V the volume and density. The formula can be read as D L  ook up the density D = 0.0002 g/mL times V, or density multiplied by of helium in Table 8.1. volume. I n place of V for volume, m = (1500 mL)D write 1500 mL. I n place of D for density, m = (1500 mL)(0.0002 g/mL) write 0.0002 g/mL. C  arry out the m = 0.3 g multiplication. That is, multiply 1500 by 0.0002. The mass of 1500 mL of helium is 0.3 g. Practice Problems 1. What is the mass of 20 000 mL of oxygen? 2. When you lower an irregularly shaped piece of copper into water in a graduated cylinder, the volume of the water increases by 6.5 mL. What is the mass of the copper? 3. What is the mass of 7.0 mL of machine oil? 314 MHR Unit 3 Fluids NL8 U2 CH08.indd 314 11/5/08 3:44:45 PM  Reading Check 1. What two measurements do you need to determine the density of a substance or object? 2. What is the formula for density? 3. Describe how to measure the volume of an object with an irregular shape. 4. If the mass of a pure substance increases, what happens to the volume of the substance? 8-2A What is the Density of a Find Out ACTIVITY Pencil? You need two measurements to calculate the 5. Determine the volume of the pencil by density of a pencil. What are they? calculating the amount of water displaced. You can calculate this value by subtracting the What You Need original volume of water from the final volume balance of the water after you submerged the pencil. 100 mL graduated cylinder 6. Calculate the pencil’s density by dividing its water mass by its volume. pencil What Did You Find Out? What to Do 1. Is the density of the pencil greater or less than 1. Use the balance to measure the mass of a the density of water? How do you know? pencil in grams. 2. How does the method you used to determine 2. Pour 90 mL of water into a 100 mL graduated the density of the pencil differ from the method cylinder. you would use for an object with a regular 3. Lower the pencil, eraser end down, into the shape, such as a cube or a sphere? cylinder. Continue to push the pencil down until it is completely underwater, but be sure Extension your finger is not also submerged. Use the same method to find out the density of 4. Read and record the new volume of water. another object, such as a rubber stopper or a cork. Make a prediction, and then carry out the activity to see if you were correct. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 315 NL8 U2 CH08.indd 315 11/5/08 3:44:47 PM  8-2B Determining Density Core Lab Skill C h e c k The following investigation will show, by means of accurate measurements, Predicting how mass and volume can be used to determine density. Measuring Question Calculating How can measurements of mass and volume be used to determine the Graphing density of a substance? Part 1 Safety Mass-to-Volume Ratios Procedure 1. Before beginning the investigation, predict how the substances will rank Handle balances with according to density. Rank the substances from the least dense (1) to care and use them most dense (5). Record your hypothesis and a brief note explaining your as instructed by your ranking order. teacher. 2. (a) Your teacher will divide the class into groups and will assign one Avoid spilling liquids and substance to each group. Subdivide each group into smaller groups sand on the balances. or partners to provide multiple trials for each substance. Do not pour substances down the drain. Dispose (b) Copy the data table below into your notebook. of them as instructed by your teacher. Individual Results Materials Substance Tested: 500 mL beaker (or 500 A B C D E mL cup) Volume Mass of Mass of Mass of Ratio of Mass balances (or one shared (mL) Beaker Only Beaker and Substance to Volume by the class) (g) Substance (g) Only (g) (g/mL) 5 different coloured 100 pencil crayons or markers 500 mL (per trial) of 200 each of the following 300 substances: water, oil, 400 glycerol, molasses, sand 500 graph paper for each student 316 MHR Unit 3 Fluids NL8 U2 CH08.indd 316 11/5/08 3:44:52 PM  Conduct an investigation Inquiry Focus 3. Measure the mass of the empty beaker. Record this value in column B of your table. Step 3. 4. Pour 100 mL of your substance into the beaker. Be as accurate as possible. Step 4. 5. Measure the mass of the beaker plus the substance. Record this value in column C in your table. 6. Subtract the mass of the beaker (column B) from the mass of the beaker and the substance together (column C). Record the difference in column D. 7. Repeat steps 3 to 5 four more times, each time adding 100 mL of your substance to what is already in the beaker. (The last time, you will be measuring 500 mL.) Step 5. Continued on next page Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 317 NL8 U2 CH08.indd 317 11/5/08 3:44:59 PM  8-2B Determining Density Core Lab Skill C h e c k 8. The mass-to-volume ratio is the relationship between mass and volume Predicting expressed as a quantity of the mass divided by its volume. To find the Measuring mass-to-volume ratio for each amount of each substance, divide the Calculating mass (column D) by the volume (column A). Show your calculations and results in column E. Wash your hands. Graphing 9. When each group has finished, your teacher will display a set of class results for all the substances in a summary chart with the following headings: Class Results Substance Mass Volume Mass-to-Volume ratio (g) (mL) (g/mL) Copy these results into your notebook. (If there were two or more trials for each substance, calculate the averages for the mass, volume, and mass-to- volume ratio values for each substance.) Part 2 Graphing Procedure 1. Make a line graph of the class results recorded in Part 1. Place the volume scale along the horizontal axis (x-axis), and the mass scale along the vertical axis (y-axis). 2. Plot the (average) results for the first substance on the graph. Draw a line through these points in one colour. Record this colour in a legend on the graph, and write the name of the substance beside it. 3. On the same graph, plot the results for the next substance. Draw a line through these points using another colour. Record this colour in the legend, and write the name of the substance beside it. 4. Repeat step 3 for the three remaining substances. 5. Give your graph a title. 318 MHR Unit 3 Fluids NL8 U2 CH08.indd 318 11/5/08 3:45:04 PM  Conduct an investigation Inquiry Focus Analyze 1. Describe the lines on your graph. Are they straight or curved? Are some lines steeper than others? Are some lines closer together than others? 2. Look back to the data table you made for your substance. What happens to the mass-to-volume ratio for each volume measurement of your substance? Why do you think this happens? 3. Compare your hypothesis to the final results. 4. There is a chance of error in every experiment. Suggest ways to improve (a) how you performed the investigation (more accurate measurement, avoidance of spilling, etc.), (b) how you calculated results (possible math errors), and (c) how you graphed your results. Conclude and Apply 5. Why are some lines in the graph similar to each other while some are different? 6. How can you tell from your mass-to-volume ratios and your graph which substance is the least dense? Which substance is the most dense? 7. Look at the mass-to-volume ratios in the Class Results table in Part 1. Compare these values with the steepness of the lines in the graph that correspond to them. How does the steepness of a line change as the mass-to-volume ratio changes? 8. Add a sixth line to your graph for a substance that is denser than water but less dense than sand. Between which values would its mass-to-volume ratio be? 9. Use the particle theory to explain the relationship between the mass, volume, and density of the substances you examined in this investigation. Extend Your Skills 10. From your observations, do you think that density and viscosity are related? Explain your answer. 11. Use the particle theory to predict the effect of temperature on mass-to-volume ratios. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 319 NL8 U2 CH08.indd 319 11/5/08 3:45:08 PM  8-2C Comparing Densities Think About It When you compare the masses of equal volumes Extension of different kinds of matter, you are comparing their densities. Scientists have recorded the densities of many substances. Does knowing how the density of a substance compares with the 1 kg gold 1 kg feathers densities of other substances tell you something about the characteristics or behaviour of the substance? Find out in this investigation. What to Do Use the information in Table 8.1 on page 312 to answer the following questions: 1. Copy and complete the diagram above by 1. Which substance in the table is the most adding a sack of gold and a sack of feathers. dense? Is it a solid, a liquid, or a gas at room If both sacks have the same mass, which one temperature? will have the larger volume? 2. Which substance is the least dense? What is its physical state at room temperature? 1 L gold 1 L feathers 3. Write a conclusion about which physical state tends to be the most dense. 4. Name the substance that is denser than mercury. Analyze 1. Which substances would float in water? 2. Which substances would sink in water? 2. Copy and complete the diagram above. Add the gold and the feathers to the measuring cups, and show how the balance would tip as a result. If both substances have the same volume, which one will have the larger mass? Record your answer. Comment on how a knowledge of density helped you with your answers. 320 MHR Unit 3 Fluids NL8 U2 CH08.indd 320 11/5/08 3:45:12 PM  The Galileo Thermometer Walking into your friend’s home, you see a large glass tube with several colourful glass balls that are suspended in liquid. While it may look like a strange piece of art, chances are you are looking at a Galileo thermometer! In the early 1600s, Galileo Galilei knew that the density of water changes as its temperature increases or decreases. He also realized that different objects that had slightly different densities would rise or sink depending on the density of the water around them. Putting these ideas together, Galileo created the thermoscope, which eventually changed into the Galileo thermometer. Modern Galileo thermometers consist of a glass tube filled with a liquid that undergoes a greater density change with temperature than water does. Also in the tube are several hollow glass balls that have been filled with coloured water. Because the glass balls are different sizes, they each have varying amounts of liquid to make them equal in weight. Attached to each glass ball is a small metal tag that has a temperature engraved on it. (For example, the red ball may be 20°C, and the blue ball may be 25°C.) If you could take these tags off and weigh them, you would find that each tag is a little different in weight. The result is that each glass ball has a slightly different density. As the temperature of the air rises, the temperature of the liquid inside the thermometer also rises. As the density of the liquid changes with the increase in temperature, it causes the weighted glass balls to either rise or sink, The glass balls filled with coloured liquid all have slightly depending on their density. The temperature of different densities. Depending on the temperature of the liquid the air can be read on the tag of the lowest ball around them, they will rise or sink. that is still suspended in the liquid. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 321 NL8 U2 CH08.indd 321 11/5/08 3:45:16 PM  Working With Density Density is really a ratio of mass to volume. For Measurements example, a 155 mL sample of glycerol is placed on a scale and records a mass of 195 g. Density is an example of a property that can be used to identify pure substances. Therefore, you could measure (a) T his would be a mass-to-volume ratio of the density of a pure substance to help determine its 195 g : 155 mL. 195 g identity. (b) This ratio can be expressed as a fraction ​ _____ 155 mL ​ In the science lab, you collect all sorts of measure- (c) You can convert this fraction to a decimal by divid- ments. Taking these measurements and turning them into ing the numerator by the denominator: numbers that allow for analysis and comparison is very 195 g ​ _____ ​= 1.26 g/mL important. In the case of density, we need to convert a 155 mL variety of mass and volume measurements to decimal values that make comparison of densities easy and make it possible to identify substances. 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. Then, compare your decimal values to Table 8.1 on page 312 to 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? 322 MHR Unit 3 Fluids NL8 U2 CH08.indd 322 11/5/08 3:45:19 PM  Checking Concepts Understanding Key Ideas 1. What is the density of a 2 cm3 sugar cube 6. How do you measure the volume of a that has a mass of 3.18 g? liquid? Of a solid? Of a gas? 2. The mass of 1 cm3 of lead is 11.34 g. 7. What does the mass-to-volume ratio tell The mass of 1 cm3 of iron is 7.87 g. you about a substance? Which solid has the greater density? 8. Why is the process of displacement a 3. Using information from Table 8.1 on good tool for measuring volume? page 312, copy the table below and fill in 9. Liquid mercury (13.55 g/mL) is denser the missing information. than solid copper (8.92 g/mL). When a drop of mercury is placed on solid Substance Mass Volume Density (g/cm3) copper, it stays on top. If mercury (g) (cm3) (Mass-to-Volume is denser than copper, why does the Ratio) mercury not move down through the aluminum 5.40 copper? 6.48 3.0 5.0 8.92 oak 0.33 salt 4.0 4. The picture shows that a can of diet soft drink floats in water, but a can of regular soft drink sinks. What does this tell you about the relative densities of water, the can of regular soft drink, and the can of diet soft drink? Pause and Reflect Dissolving substances such as salt into 5. Explain why the lines representing pure water increases the density of water. Salt substances on a mass vs. volume graph water has a greater density than distilled are straight. (pure) water. Considering the formula you have learned for calculating density, offer an explanation for why salt water is denser than distilled water. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 323 NL8 U2 CH08.indd 323 11/5/08 3:45:22 PM  8.3 Changes in Density Just as changes in temperature affect the viscosity of fluids, changes in temperature also affect the density of a substance. By learning about the effects of temperature on density, you will begin to understand how these two factors are linked together in the world around us. Changes in Temperature and Density As you know, as temperature increases, a substance will change Suggested Activity from a solid, to liquid, to gas. The particle theory states that Find Out Activity 8-3B on the particles of a substance spread out as they gain energy when page 328. heated. Since they spread out, the particles take up more space, which means that the density of a substance decreases. It is almost always true that, for each pure substance (for example, silver), the density of its solid state is greater than the density of its liquid state. The substance’s solid state and liquid state are, in turn, denser than its gaseous state. Although most substances are denser in their solid form, water is an exception to this rule. When water freezes, the particles move slightly farther apart as they become fixed in position. This means that ice is actually less dense than liquid water, so it floats. Figure 8.11 The property of ice floating on water makes life in freshwater lakes possible. If ice sank as it froze, lakes would freeze solid. Instead, the floating ice builds slowly from the top down, creating an insulating barrier against cold temperatures. Temperature and Density in Everyday Life You don’t have to conduct an experiment in your science classroom to see the effects of temperature on density. All you have to do is look around you. For example, have you ever noticed that the tires on an automobile need more air during the winter than they do during the summer? As the temperatures 324 MHR Unit 3 Fluids NL8 U2 CH08.indd 324 11/5/08 3:45:24 PM  decrease in the winter months, the particles inside the air in the tires lose energy, and therefore, take up less space. Therefore, the density of the air decreases, and the tire deflates a little. During the summer, however, increasing temperatures give the air particles more energy, meaning they require more space to move around. The air in the tire then expands, and the tire inflates. A hot-air balloon is another example of the effect of temperature on density. When a balloon pilot is preparing to fly, you will notice that he or she turns on Figure 8.12 A hot-air balloon rises by adding heat to the air, and a gas burner that heats the air inside the balloon. As they gain therefore decreasing the density of energy from the heat, the air particles inside the balloon begin to the air inside the balloon. move around more and spread further apart from one another. Eventually, the air particles move so far away from each other that some of them are forced out of the bottom of the balloon. As the density of the air inside the balloon decreases, it becomes less dense than the air surrounding the balloon, so it rises. The pilot can now control the altitude of the balloon by controlling the amount of heat that enters the balloon. 8-3A Lava Lamps Think About It In this activity, you 1. What happens to the density of the wax in will discover how the relation to the water when it is heated? "lava" flows inside a 2. As the density of the wax changes, what lava lamp. happens to it? At the bottom of a 3. Once the wax reaches the top of the lamp, it lava lamp sits an begins to flow back down. Why? incandescent bulb, 4. Using the particle theory, explain in your own which heats up the words how a lava lamp works. mixture of water and wax that sits at the bottom of the glass when it is cold. At room temperature, the wax is slightly denser than water. By answering the following questions and using your knowledge of density, see if you can figure out how the “lava” moves up and down. Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 325 NL8 U2 CH08.indd 325 11/5/08 3:45:28 PM  Changes in the density of a substance can also occur naturally. If you have ever stacked wood, you will know that freshly cut Did You Know? wood from a living tree is much heavier than wood that has Have you ever gone swimming been cut and dried in the air for a period of time. Why is this? in the ocean? If you have, then A living tree, or one that has been freshly cut, contains a high you know that it is much easier quantity of water. In fact, the water in a living tree often has to float in salt water than in a greater mass than the wood itself. The density of a living or fresh water. The reason is that freshly cut tree is, therefore, high due to its high water content. the density of salt water is greater than that of fresh water. Once a tree has been cut and is left to dry, the water particles Therefore, it can support more in the wood evaporate, and are replaced with air. Because air is of your body weight, making it much less dense than water, the dry wood is less dense than the easier for you to float. moist wood. Therefore, the wood is lighter and easier to lift. As well, the absence of water makes the wood easier to burn. Figure 8.13 Firewood is often stacked and left to dry before being used. As the water evaporates, the density of the wood decreases, making it lighter and easier to burn. 326 MHR Unit 3 Fluids NL8 U2 CH08.indd 326 11/5/08 3:45:30 PM  Iridium—The Densest over the world that contained iridium. This dust would have also blocked out the Sun for a long Substance on Earth period of time, bringing an end to many plant and Imagine a substance that is so resistant to heat, animal species, including the dinosaurs. its melting point is at 2446°C and its boiling point Iridium is used in is at 4428°C. What kind of uses can you think of unmanned space probes, for a substance like that? The substance is iridium, such as the Voyageur and it is the densest known substance on Earth. probes, to enclose electrical generators to Discovered in 1803, iridium is a very hard and protect them from high brittle metal that was named after the Greek word temperatures. iris, meaning "rainbow." Although it looks silvery- white, the salts that are in iridium ore are many different colours. Canada is the primary source for iridium, which is a by-product of nickel mining. With such unique properties, iridium has many uses. It is an ingredient in crucibles, electrical contacts such as spark plugs, and platinum jewellery. It is also used in cancer radiation therapy. Iridium and the Dinosaurs? There is one theory that iridium may have caused the extinction of Because of its high tolerance for the dinosaurs. heat, iridium is often used in making All over the crucibles that can be heated to high temperatures to melt metals. world’s surface, there is a layer of iridium in the Iridium is used as a hardening agent in sediment. As platinum. This allows iridium is found jewellery, such as these in meteors, platinum rings, to be more scientists durable. believe that Earth was struck by a large meteor during the time of the dinosaurs. The impact of the meteor would have created clouds of dust all Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 327 NL8 U2 CH08.indd 327 11/5/08 3:45:35 PM  8-3B Layers of Water Find Out ACTIVITY In this activity, you can find out how the 5. To make sure the hot water enters gently, have temperature of a liquid affects its density. your partner hold the head of the spoon at the top of the cold water level. Pour the hot water Safety into the head of the spoon. Continue pouring very slowly until the beaker is full. 6. Observe your beaker. If you have created two Be careful when handling hot water. layers, look at them very carefully, especially Materials where the two layers meet. If you do not two 250 mL beakers stirring rod have two layers, look at the beakers of other very cold water large spoon students in class. very hot water food colouring 7. Clean up and put away the equipment you have used. 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 with the hot and cold water not forming layers. Provide an explanation, based on the particle theory, as to why the layers sometimes do not form. What to Do 3. How does the kinetic energy (energy of motion) and distance between particles 1. Add 100 mL of water to a beaker. Use water as compare between hot water and cold water? cold as possible from the tap. 4. If you repeated this activity by trying to pour 2. Add 100 mL of water to the other beaker. Use the cold water on top of the hot water, what water as hot as possible from the tap. Do not do you think would be the result? Explain. burn yourself. Use protective mitts to handle your hot water beaker. 3. Add a few drops of food colouring to the hot water and stir. 4. Put the stirring rod across the top of the hot water beaker, and very gently tip it so that the water runs along the stirring rod into the cold water beaker. 328 MHR Unit 3 Fluids NL8 U2 CH08.indd 328 11/5/08 3:45:38 PM  Checking Concepts 3. In picture below is an outdoor 1. The photograph shows six substances— thermometer. It is made of a small tube oil, corn syrup, water, plastic, with a quantity of coloured alcohol. We Styrofoam®, and a grape—layered in a can tell how warm or cold it is outside cylinder. Based on how they are layered, by reading the temperature that is next place these six substances in a list from to the top of the coloured alcohol lowest to greatest density. line. Using your knowledge about temperature and density, explain how the alcohol moves up or down, depending on the temperature. 2. A balloon is filled with helium in a cold room. The balloon is taken to a warm room where, after some time, the balloon expands. Has the density of the helium changed? Explain. Pause and Reflect Understanding Key Ideas 4. Use the particle theory to explain how A weather balloon is a type of unmanned temperature affects density. balloon that takes readings of atmospheric 5. Explain why the properties of water are pressure, temperature, and humidity. Unlike critical for the survival of living organisms hot-air balloons that are usually made of a in the water during winter. type of nylon fabric, weather balloons are made with a flexible latex material. Why do you think weather balloons are made of this type of material rather than a nylon fabric? Chapter 8 Density describes the amount of mass in a given volume of a substance. MHR 329 NL8 U2 CH08.indd 329 11/5/08 3:45:43 PM  Chapter 8 Prepare Your Own Summary 8. What two factors must remain the same In this chapter, you explored fluids by for the density of a pure substance to learning how to calculate their densities, stay constant? and by examining factors that increase or 9. Changes in temperature can often decrease their density. Create your summary change the density of a substance. of the key ideas from this chapter. You may Provide one example of this effect. include graphic organizers or illustrations Explain why the temperature change of with your notes. Use the following headings the substance affects its density. to organize your notes: 1. Densities of Solids, Liquids, and Gases Understanding Key Concepts 2. Calculating Density 10. The graph below shows the density of 3. Effect of Temperature on Density three different substances. 4. Temperature and Density in Everyday Life