DENSITY A summary

Mass Mass is the amount of material in an object. Mass is measured with a balance, usually in grams or kilograms.

Volume Volume is the amount of space occupied by an object. It is measured using a graduated cylinder or calculated using objects dimensions Volume is measured in cm 3, m 3, mL and L.

Block If the object is a square or rectangular block, use the formula V = l x w x h to calculate volume.

Cylinder If the object is cylindrical, use V =   r 2  h to calculate volume.

Liquid If the substance is a liquid, just measure its volume with a graduated cylinder.

For Irregular-shaped Objects: Use the method known as displacement. Fill a graduated cylinder (or container with a scale) with a set amount of water and record the volume (i.e. 50 mL) Carefully add the irregular-shaped object to the cylinder and record the new volume (i.e. 53 mL) Subtract the initial volume from the new volume – (i.e. 53mL - 50mL) The volume of the irregular-shaped object must be 3 mL.

Volume using Graduated Cylinder

For large, irregular-shaped objects: Use the method known as overflow. Fill an overflow can with water and place an empty graduated cylinder under the spout. Carefully add the irregular-shaped object to the overflow can and record the volume of water in the graduated cylinder (i.e. 85 mL). The volume of the irregular-shaped object must be 85 cm 3 (since 1 mL = 1 cm 3 ).

Displacement of Water

Density Density is a mass to volume ratio Density is a physical property and is unique to each pure substance Objects with smaller densities will float in liquids that have greater densities With one exception….

Water! Particles of solid matter are usually much closer together than they are in the liquid state What’s happening here?

Water The particle theory is not true for water! – Solid state is less dense than liquid - so it floats! Another unique property of water is its ability to dissolve a large variety of chemical substances – Universal solvent Waters boiling point is unusually high

Density Density depends on: a) The mass of each particle b) How tightly packed the particles are The density of a solid is usually greater than that of a liquid – What about water? The density of liquid is usually greater than that of a gas

Density of Common Substances SUBSTANCESTATE AT 20 0 C DENSITY AT 20 0 C ( g/cm 3 ) goldsolid19.32 Leadsolid11.35 silversolid10.5 coppersolid8.93 nickelsolid8.9 ironsolid7.88 aluminiumsolid2.7 glasssolid2.7 rubbersolid1.2 oak(wood)solid pine(wood)solid Styrofoamsolid0.005 Which substance is most dense? Least dense?

Density Formula D = m/V D = density (g/cm 3 ) m = mass (g) V = volume (cm 3 ) Correct case is essential: M = magnification, d = distance, v = speed

Let’s find some density! Problem: A sample of silver has a mass of 5.04 g and a volume of cm 3. What is the density of silver? The volumes for mass and volume are given: m = 5.04g and V = cm 3 The equation for density is D = m/V Substitute values: D = 5.04g/ cm 3 D = 10.5 g/cm 3 The density of silver is 10.5 g/cm 3

You Try! Work on Density Calculations Worksheet 1 – Use the GRASS method! G: Given – write out the variables given in a column R: Required – What are you required to find? A: Analysis – write out the equation you are going to use S: Solve! S: Sentence – answer the question with a final sentence – Please finish for homework (use GRASS)

1 more thing… The Magic Density Triangle: Cover up the variable you are trying to find – m = D/V – D = m/V – V = m/D