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DENSITY Let’s understand it once and for all! TO CALCULATE Mass Density = -----------Volume OR m D = ----v THE TRIANGLE TRICK m D v On your paper, draw the triangle and write the three formulas you can derive from this triangle. UNITS For mass, units may be grams, kilograms, centigrams, etc. For liquid volume, units may be liters, milliliters, kiloliters, etc. For solid volume, units may be cubic centimeters, cubic meters, etc. DERIVED UNITS The unit for density is a derived unit because it is a combination of two other units. Just as you divide the numbers to solve the problem, you also divide the units. Ex. If mass is in g, and volume is in cm3, then the units for density will be: g ----cm3 QUESTION What would be some possible units for the density of a liquid? LET’S DO SOME WORK What is the density of 10 mL of a substance with a mass of 8 g? m D = ---v 8g D = ------10 mL g D = 0.8 ---mL MORE WORK TO DO Now, we will figure the density of half the amount of the same substance. – What is the mass? 4 g – What is the volume? 5 mL g – -----------What is the density? 0.8 ----mL SAME AS BEFORE!!! WHY??? DENSITY IS A PHYSICAL PROPERTY Density does NOT depend on a substance’s shape or size. Density for a substance does NOT change whether the substance is in a big amount or a small amount. Density depends on a substance’s chemical composition, pressure, and temperature. If any of these things change, the density may change. TAKE WATER FOR EXAMPLE The chemical formula for water is H2O. g Water has a density of 1.0 --- . mL A single drop of water has that density. A bathtub full of water also has that density. The mass increased, but so did the volume. The ratio of the two after dividing is the SAME. WILL IT FLOAT? If a substance has a density that is less than the density of water, it will float. If it has a density that is more than the density of water, it will sink (it is heavier). Will the substance from our earlier work float in water? MORE WORK Calculate the volume of an object if you know that the object has a mass of 14 grams and the density is 12 g/mL. Calculate the mass of an object if you know that the object has a density of 13 g/mL and the volume is 5 mL. Calculate the density of a liquid in a beaker. The beaker has a mass of 15 grams when empty. The beaker plus an unknown liquid has a mass of 43 grams. What is the density of the liquid if its volume is 10 mL? Identify the materials in the density column to the right by using the data table to help you. 40 mL Liquid Material Material A Milk 30 mL Material B 20 mL Fingernail Material C Polish Remover 10 mL Density (g/ml) 1.02 0.78 Olive Oil 0.92 Citric Acid 1.66 Material D