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 cm3, m3, 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 = r2 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 cm3 (since 1 mL = 1 cm3).

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

SUBSTANCE STATE AT 200CDENSITY AT 200C

( g/cm3)gold solid 19.32Lead solid 11.35silver solid 10.5

copper solid 8.93nickel solid 8.9iron solid 7.88

aluminium solid 2.7glass solid 2.7

rubber solid 1.2oak(wood) solid 0.7 -0.9pine(wood) solid 0.4 -0.5Styrofoam solid 0.005

Which substance is most dense? Least dense?

Density Formula

D = m/V

D = density (g/cm3)

m = mass (g)

V = volume (cm3)

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 0.480 cm3. What is the density of silver?

The volumes for mass and volume are given:

m = 5.04g and V = 0.480 cm3

The equation for density is D = m/V Substitute values: D = 5.04g/ 0.480 cm3

D = 10.5 g/cm3

The density of silver is 10.5 g/cm3

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