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Density Test Review Standard II: Objective 1 What is the density of a log that is floating in a lake? It is less dense than water and denser than the air above it. A rock and a lead weight both sink when dropped into a lake. What do you know about their densities? They are both denser than air and water. Water has a density of 1g/mL. What density might a typical rock have? 5g/mL Substance Oil Water Plastic Marble Aluminum Density .8 g/mL 1.0 g/mL .9 g/ cm3 4.2 g/ cm3 2.3 g/ cm3 When poured together in a jar, what would be the order of the substances starting from the bottom of the jar and going up? Marble, Aluminum, Water, Plastic, Oil If these substances were all placed in a test tube together, where would a substance with a mass of 14 g and 20 mL float? You must first do the math to find the density. On top of the oil How would a student find the volume of an irregularly shaped piece of rock? By water displacement… find the volume of a liquid, add the rock, count the change in volume. That’s the volume of the rock. This method is called water displacement. If the volume of a rock is 8 cm3 and its mass is 16g, what is its density? Mass/volume=2g/cm3 Why is finding the density of gasses difficult? Because it is difficult to contain them AND finding the mass is difficult because gasses don’t have a lot of mass so you need sensitive equipment. A student collected data about the density of air. She found that .1g of air had a volume of 100cm3. What is the density of air? Mass/volume=.001g/cm3 A rock dropped in a graduated cylinder raises the level of water from 20 to 35 mL. The rock has a mass of 45 g. What is the density of the rock? You must first find the volume which the difference between 35 and 20=15 mL. Then calculate density by dividing mass by volume mass/volume=3g/mL. A liquid is found to have a volume of 75 mL in a graduated cylinder. When placed on a balance the liquid and the graduated cylinder has a mass of 125 g. The empty cylinder has a mass of 50g. What is the density of the liquid? Find the mass by subtracting the mass of the empty container from the mass of the filled container. Mass=75 g. Mass/volume=1g/mL A liquid has a density of 1g/mL. If you have 50 mL of the liquid, what would its mass be? 1 g/mL means for every mL there is one gram of substance. So if there’s 50 mL you multiply that number to the number of grams and you have the total mass for the amount of volume. A square chunk of plastic has a length of 5 cm, width of 5 cm and a height of 5 cm. It has a mass of 200g. What is its density? You must first find the volume by multiplying length, width and height which =125cm3. Mass/volume=1.6g/cm3 Water is added to a jar with soil and gravel in it and the jar is shaken. Draw what will happen after the jar sits for a few minutes. Use dots to show particle size. A student shakes a jar with a mixture of sand and gravel types. Instead of mixing, the sand grains separate into layers. Why? Because they are different sizes. Students mixed sand, gravel, clay and humus in a jar with water and shook it. The substances settle in the jar as pictured below. Why did the gravel settle first? Because it’s large If this were a river, which Sediment would wash Away first? Humus because it suspends in water easily In the spring, rivers in Utah are often brown in color because they contain very small particles of sediment called silt. Why is silt suspended in the water? The water is moving a lot and silt particles are so small they float in water easily. In winter, a layer of cold air settles in the valleys and warmer air is often found higher in the mountains. What might account for this condition? Cold air is denser than warm air. A beach is composed of particles of sand of the same size. Why doesn’t the beach have materials of all sizes? The particles have … Been sorted by size and density. A streambed contains round rocks, all about the same size. Why are there no smaller particles of sand and clay. Sand and clay… Have washed away A gold miner shakes a mixture of mud and water in a gold pan. He looks for gold at the bottom. Why? Gold is very dense and sinks. In an experiment, a student shakes jars of water with soil and rock in them. What does the shaking model in nature? This models a stream current. Which question would help a student learn more about the behavior of materials in a mixture? What happens to soil after a landslide? The study of a lake shows that an incoming stream deposits larger particles as it enters the lake and smaller ones in the center of the lake. What inference can be make from these observations? The particles are being sorted by size. Standard II: Objective 2 Earth’s interior is divided into layers. What are the four divisions, in order, of least dense to most dense? Crust, mantle, outer core, inner core The mantle is a layer of Earth. What is its density compared to other layers? It is denser than the layers above it and less dense than the layers below it. Which layer of the Earth is most dense? The inner core Why is air less dense than Earth’s rocks? Air is less dense because the molecules are farther apart in air than in rocks. How does density affect the organization of Earth? The densest material is closest to the center, causing layers. Earth’s rigid crust floats on the hot, plastic material of the mantle. What conclusion should be made about their density. The crust is… Less dense and floats, it doesn’t matter if it is a solid. Wood is a solid and it floats on water because it is less dense. From Earth’s surface to its center, the layers of Earth’s interior differ in their composition, temperature and pressure. This diagram shows the layers. What conclusion can you make about the density of Earth layers from the diagram? As temperature and pressure increases, density increases. Which layer is densest? The inner core is densest. Why is the atmosphere above the crust? Air is less dense than the crust How are the materials making up the core different from those of the crust? They are more dense The following materials are available to build a model of Earth: Clay, a hard ball, aluminum foil, cotton balls, cardboard Which substance would be the best model for the mantle? Clay because it can be molded and change shape like the mantle is a plastic liquid so is clay Which substance would best model the thickness of the crust? Aluminum foil A collection of rocks is used to model the kinds of materials found in Earth. Which rock should be labeled “core” rocks? The rocks made of iron/nickel Which model of Earth shows the most accurate shape and relative size of the continents? A road map, a topographical map, a globe, a poster? A globe shows relative size the best. Which parts of this model are accurate? The names of the layers How could the crust be more accurately represented? It needs to be thinner and flattened out. THE END