Density

1. Density S1/Physics/Gr7/Rifki/2011 - 2012

2. Archimedes ( 287 – 212 BC ) “density is defined as its mass per unit volume - equation - “density is defined as its mass per unit volume m (kg) mass ρ(kg ∙ m-3) = Density = V (m3) volume

3. Density is measured in kilograms per cubic metre( kg ∙ m-3 ) or grams per cubic centimetre( g ∙ cm-3 ) 1 g ∙ cm-3 = 1000 kg ∙ m-3 “density can be measured as the mass of 1 cm3 of any substance - equation - 1 cm 1 cm 1 cm

4. Example 1. Taking the density of copper as 9 g ∙ cm-3 find : the mass of 5 cm3 the volume of 63 g Known : ρ= 9 g ∙ cm-3 V = 5 cm3 m = 63 g Question : a. m (g) b. V (cm3) Answer : a. m = V x ρ = 5 cm3 x 9 g ∙ cm-3 = 45 g b. V = m / ρ = 63 g/ 9 g ∙ cm-3 = 7 cm3

5. Exercise (text book pg. 53) : • a. If the density of wood is 0.5 g/cm3 what is the mass of • 1 cm3 • 2 cm3 • 10 cm3 • What is the density of a substance of • mass 100 g and volume 10 cm3 • volume 3 m3 and mass 9 kg • The density of gold is 19 g/cm3 . Find the volume of • 38 g • 95 g of gold.

6. A piece of steel has a volume of 12 cm3, and a mass of 96 g. What is its density in : • g / cm3 • Kg / m3 • What is the mass of 5 m3 of cement of density 3000 kg/m3 • What is the mass of air in a room measuring 10m x 5.0m x 2.0m if the density of air is 1.3 kg/m3? • When a golf ball is lowered into a measuring cylinder of water, the water level rises by 30 cm3 when the ball is completely submerged. If the ball weighs 33 g in air, find its density.

7. A block of aluminum occupies a volume of 15.0 mL and weighs 40.5 g.What is its density? • Mercury metal is poured into a graduated cylinder that holds exactly 22.5 mL. The mercury used to fill the cylinder weighs 306.0 g. From this information, calculate the density of mercury. • What is the weight of the ethanol that exactly fills a 200.0 mL container? The density of ethanol is 0.789 g/mL. • A rectangular block of copper metal weighs 1896 g. The dimensions of the block are 8.4 cm by 5.5 cm by 4.6 cm. From this data, what is the density of copper? (hint: find the volume of a block first) • What volume of silver metal will weigh exactly 2500.0 g. The density of silver is 10.5 g/cm3. • Find the mass of 250.0 mL of benzene. The density of benzene is 0.8765 g/mL. • A block of lead has dimensions of 4.50 cm by 5.20 cm by 6.00 cm. The block weighs 1587 g. From this information, calculate the density of lead.

8. Floating and Sinking “an object sinks in a liquid of lower density than its own “an object float, partly or wholy submerged in a liquid of higher density than its own wood ρ = 0.65 g ∙ cm-3 copper ρ = 8.92 g ∙ cm-3 water ρ = 1 g ∙ mL-1

9. Experiment 1 : Liquid Rainbow Materials: 4 large containers (e.g., pitchers or milk jugs), food coloring (4 colors), transparent drinking straws, pickling salt (preferred), 5 vials or test tubes per student group (4 for solutions and 1 for waste) Lab Safety Never taste any chemical. Do not pour the chemicals back into the wrong dispensing container and thereby contaminate a large quantity. Never mouth pipet. This activity is indirectly adapted (through McREL) from the activity “Layering Liquids” featured in the Great Explorations in Math and Science (GEMS) curriculum, “Discovering Density.” Find data sheets to supplement and guide this activity in this publication. http://www.lawrencehallofscience.org/gems/GEM300.html

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11. mL mL mL mL 50 50 50 50 40 40 40 40 30 30 30 30 20 20 20 20 10 10 10 10

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