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DENSITY. Let’s understand it once and for all!. Mass Density = ------------ Volume OR m D = ----- v. TO CALCULATE. m. D. v.
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DENSITY Let’s understand it once and for all!
Mass Density = ------------ Volume OR m D = ----- v TO CALCULATE
m D v THE TRIANGLE TRICK 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 8 g g D = ---- D = ------- D = 0.8 ---- v 10 mL 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?
Material A Material B Material C Material D 40 mL 30 mL 20 mL 10 mL Identify the materials in the density column to the right by using the data table to help you.