DENSITY Here's an old joke: What weighs more, a pound of bricks or a pound of feathers? The answer is they both weigh the same. Which takes up more space though? Obviously, the pound of feathers takes up way more space (has a greater volume). This leads to a very useful property of matter called DENSITY. DENSITY FACTS Most kinds of matter expand when their temperatures rise and contract when their temperatures drop. Thus, density changes with temperature. Very cold water is denser than hot water because the water molecules are closer together. So as temperature increases, density decreases. The bottom line is that density is not constant. At 4°C pure water has a density of about 1 g/cu.cm, 1 g/ml. What is the density of ice? Demonstrations: Water and ice: What can you infer about the density of these items? Gases are always less dense than liquids and solids. That’s why air bubbles in a glass of water move upward and escape. The solid states of matter generally have higher densities than do the liquids. One very important exception to this rule is ordinary water. Water expands when it freezes. The H2O molecules arrange themselves in a pattern that takes up more space than when the molecules are in the liquid state. Therefore, ice floats in water. Demonstrations: Water and oil: What can you infer about the density of these items? Soda vs. Diet Soda: What can you infer about the density of these items? Dead Sea Substances that have a density less than water's will float in water. Substances with a greater density than water's will sink. Life jackets make us less dense than water, so we float. Submarines can change depth in the water when they remove or add water to special tanks called ballast tanks. When water is removed from the tanks, the submarine loses mass. It floats higher in the water. When water is added to the tanks, the submarine gains mass. It sinks lower in the water because its density is now greater. What is the density of a rock that has a mass of 25.2 g and a volume of 11.9 mL? Use the 3-step method to solve this problem: 1) Write the formula. D = M/V 2) Plug in the numbers and units. D = 25.2g / 11.9 mL 3) Complete the calculation and show the correct unit for density. D = 2.1 g/mL Density is a measure of how closely the particles of a substance are packed into a given space. Density is found by measuring mass and volume and then dividing the mass by the volume. The formula for density is: D = M/V D stands for density, M stands for mass, and V stands for volume. What is the density of a rock that has a mass of 32.5 g and a volume of 12.8 mL? Use the 3-step method to solve this problem: 1) Write the formula. D = M/V 2) Plug in the numbers and units. 3) Complete the calculation and show the correct unit for density. What is the density of a rock that has a mass of 32.5 g and a volume of 12.8 mL? You have a rock with a volume of 15cm3 and a mass of 45 g. What is its density? Click for answer You have a different rock with a volume of 30cm3 and a mass of 60g. What is its density? Click for answer What is the density of a board whose dimensions are 5.54 cm x 10.6 cm x 199 cm and whose mass is 28.6 Kg? Show your answer in grams/cubic centimeters. Click for answer You have a rock with a volume of 15cm3 and a mass of 45 g. What is its density? Back to Problems You have a different rock with a volume of 30cm3 and a mass of 60g. What is its density? Back to Problems What is the density of a board whose dimensions are 5.54 cm x 10.6 cm x 199 cm and whose mass is 28.6 Kg? D = M/V 5.54 cm x 10.6 cm x 199 cm = 11686.0cm3 28.6 Kg 11686.0 cm3 D= .002447373 kg/cm3 D= .002447373 kg/cm3 .002447373 k h da g d c m .02447373 .2447373 D = 2.45 g /cm3 2.447373 Back to Problems Substance Density (g/cm3) Substance Density (g/cm3) Platinum 21.4 Seawater 1.025 Gold 19.3 Water 1.00 Mercury 13.6 Ice 0.92 Lead 11.3 Oil 0.90 Silver 10.5 Paraffin (wax) 0.87 Copper 8.9 Gasoline 0.7 Brass 8.5 Wood (oak) 0.7 Iron 7.9 Wood (pine) 0.4 Steel 7.8 Cork 0.24 Aluminum 2.7 Oxygen 0.0014 Marble 2.69 Air 0.0013 Rubber 1.1 Helium 0.0002 Work these problems in your notebook..... 1. A man is buying a copper bowl because he heard it is the best material to whip egg whites in. If the bowl has a mass of 142 g and a volume of 15.95 mL, is it a real copper bowl?. 2. What volume would a 0.451 gram sample of air occupy if the density of air is 1.29g/L? 3. Explain the beaker in the front of the room in terms of density. 1. A man is buying a copper bowl because he heard it is the best material to whip egg whites in. If the bowl has a mass of 142 g and a volume of 15.95 mL, is it a real copper bowl? D= 142g / 15.95 mL D= 8.9 g/mL Is it copper? YES! 2. What volume would a 0.451 gram sample of air occupy if the density of air is 1.29g/L? D= M/V 1.29 g/L = 0.451 g/ V make it simple 12=36/3 1.29 g/L = 0.451g/ .349 L 3. Explain the beaker in the front of the room in terms of density. The yellow liquid at the top of the beaker is less dense than the other substances. The bluish substance is more dense than the top substance, but less dense than the bottom substance. The red bottom substance is the most dense. Essays must be between 700 to 1,000 words in length, include a list of research sources, and fall under one of these four categories: Together, we can feed the world. Together, we can build a secure energy future. Together, we can protect people and the environment. Together, we can be innovative anywhere. Dupont Science Essay Challenge Write the following in each line, from most dense to least dense.... water, oil, ice gasoline, mercury, iron air, oxygen, helium sea water, ice, water water, ice, oil mercury, iron , gasoline oxygen, air, helium seawater, water, ice Acrylic-clear Aluminum- shiny silver Brass- gold colored Copper- copper, reddish Oak-darker wood Pine-lighter wood Polypropylene-cloudy PVC-dark gray Steel-lighter gray, metallic, heavy Substance Mass (g) L (cm) W (cm) H (cm) Volume (c m3) Density (g/cm3) Sink or Float? D=M/V Acrylic Aluminum WRITE EQUATIONS IN Brass MARGIN Copper Oak Pine Polypropylene PVC Steel Substanc Mass (g) e L (cm) W (cm) H (cm) Volume ( cm3) Density (g/cm3) Sink or Float ? Acrylic 18 g 2.5cm 2.5cm 2.5cm 15.6 cm3 1.1-1.2 g/cm3 S Aluminu m 43 g 2.5cm 2.5cm 2.5cm 15.6 cm3 2.7 g/cm3 S Brass 134 g 2.5cm 2.5cm 2.5cm 15.6 cm3 8.4-8.8 g/cm3 S Copper 144.3 g 2.5cm 2.5cm 2.5cm 15.6 cm3 8.94 g/cm3 S Oak 11.0 g 2.5cm 2.5cm 2.5cm 15.6 cm3 0.6-0.9 g/cm3 F Pine 7.5 g 2.5cm 2.5cm 2.5cm 15.6 cm3 0.35-.50 g/cm3 F Polypropyle ne 15 g 2.5cm 2.5cm 2.5cm 15.6 cm3 0.91-.94 g/cm3 F PVC 22.2 g 2.5cm 2.5cm 2.5cm 15.6 cm3 1.39-1.42 g/cm3 S Steel 126.2 g 2.5cm 2.5cm 2.5cm 15.6 cm3 7.9 g/cm3 S Density Lab INTRO: Understanding the concept of density is very important in the world of science as well is in our everyday lives. Scientists use density calculations to help analyze how “tightly packed” a material’s particles are. They also use this calculation to be able to identify various materials due to the fact that each substance has a unique density. In our lives, we use the concept of density to understand the relationship between different types of materials. We use terms such as hardness or heaviness to describe the density of various items in our daily language. PURPOSE: The purpose of this lab is for you to practice gathering mass and volume measurements as well as to use your collected data to make density calculations. PROCEDURE: Eight items are listed in the table on the data sheet for this lab. Record the mass, volume, method for finding volume, and density in the table. MASS - To measure mass, use a triple-beam balance. Be sure to round your measurement values to the nearest tenth of a gram (one decimal place) and to include a label after the number. VOLUME - To measure volume, choose one of the various options available (listed below) and be sure to include a label with your final answer (either mL or cm3). reading a graduated cylinder multiplying length x width x height water displacement (using a graduated cylinder and/or a spill can) DENSITY - Calculate density using the three-step method discussed in class. Round your answer to the tenth. Be sure to label your answer appropriately. Compare your answer to the correct answer posted at the front of the room. If your answer is not close to this, you will need to re-do your measurements and calculate the density again to get closer to the correct answer. Substanc e Glycerine Methyl Alcohol Wood Rubber Stopper Wax Rock (Granite) Mineral Oil Water Mass(g Volume ( ) cm3 or mL) How you found volum e Density (g/ml or g/cm3(three-step method) APPLYING WHAT WE HAVE LEARNED Would gasoline float OR sink if mixed with water? _______________ Would an ice cube float OR sink if dropped in oil? _______________ Does helium gas float OR sink in air? _______________ Mercury is a liquid at room temperature. Would an iron bolt float OR sink in mercury? _______________ Write the formula for density: ________________________________________ What equipment is used to measure an item’s volume? ______________________ What label(s) do we commonly use to represent volume? ____________________ What equipment is used to measure a substance’s mass? _____________________ What label do we commonly use to represent mass? _______________ Is it easier to measure the volume of a liquid or a solid? Explain your answer. __________________________________________________________________ __________________________________________________________________ Do you feel that this lab has helped you develop a better understanding of the concept of density? Explain. __________________________________________________________________ __________________________________________________________________ Density Worksheet Density is the ratio of the mass of the substance to the volume of the substance at a given temperature. Density has units of g/ cm3 or g/cc or g/mL for liquids and solids, and g/L for gases. SHOW YOUR WORK! 1. A gold-colored ring has a mass of 18.9 grams and a volume of 1.12 mL. Is the ring pure gold? (The density of gold is 19.3 g/mL.) 2. What volume would a 0.871 gram sample of air occupy if the density of air 1.29 g/L? 1.29g/L = 0.871g / V (4= D=18.9g / 1.12 mL 12/3) .871g/1.29g/L= .675 L D= 16.87 g/mL 3. Pumice is volcanic rock that contains many trapped air bubbles. A 225 gram sample occupied 236.6 mL. What is the density of pumice? Will pumice float on water? D = 225g/236.6mL D= . 95 Yes, pumice will float in water! 4. A cup of sugar has a volume of 237 mL. What is the mass of the cup of sugar if the density is 1.59 g/mL? 1.59g/mL = m / 237 mL 1.59 x 237 = 376.83 m = 376.83 g 9 = 27/3 5. From their density values, decide whether each of the following substances will sink or float when placed in sea water, which has a density of 1.025 g/mL. Float Gasoline 0.66 g/m Sink Mercury 10.6 g/mL Float Cork 0.26 g/mL 6. A sample of lead is found to have a mass of 32.6 g. A graduated cylinder contains 2.8 mL of water. After the lead sample is added to the cylinder the water level reads 5.7 mL. Calculate the density of the lead sample. 5.7 mL -2.8 mL 2.9 mL D= 32.6 g / 2.9 mL D=11.24 g/mL 7. A little aluminum boat (mass of 14.50 g) has a volume of 450.00 cm3. The boat is place in a small pool of water and carefully filled with pennies. If each penny has a mass of 2.50 g, how many pennies can be added to the boat before it sinks? Mass to Volume must be greater than 1 g/mL 450cm3 = 450 mL needs to be greater than 450 g to sink 450 g - 14.5 g of boat = 435.5 g 435.5 g/ 2.5 g (penny) 174.2 pennies to equal density 175 pennies to sink da boat! 8. Density varies with change in temperature. Why? If the temperature changes, then the particles move further apart, cause thermal expansion to occur, which would make a higher volume, which would cause a change in density. 9. The King of Artemesia was given a gift of a crown of gold, but he suspected that he was being fooled. He asked his court scientist (that’s you) to prove if the crown was really gold or not. You found the mass of the crown was 452.3 g. The volume of the crown was 53.2 ml. Is the crown made of gold? Include as much detail as you possibly can to prove your point. Use your Density Reading for help. If the crown is not made of gold, what material is it made of? How do you know? D= 452.3 g / 53.2 mL D = 8.50 g/mL The crown can not be gold, as the density of gold is 19.3 g/mL. With a density of 8.5 g/mL, the crown must be made out of brass. Brass looks like gold, but is not gold at all! Brass is made up of an alloy of zinc and copper.