Density

Density = Mass per unit volume = Mass / Volume

• Unit of density is kilograms per cubic metre (kgm^-3)
• Gases are much less dense than solids because the average separation between molecules in a gas is much greater than a solid or liquid

Density of a few common examples (in kgm^-3):

• Air - 1.2
• Aluminium - 2700
• Copper - 8900
• Gold - 19300
• Hydrogen - 0.083
• Iron - 7900
• Lead - 11300
• Oxygen - 1.3
• Silver - 10500
• Water - 1000

An unknown substance can be identified if its density is measured and compared with outher materials through the following methods...

Volume equations:

Cuboid = lenght x base x width

Cylinder =pi x d^2     x h

                    4

Sphere = 4 / 3 pi x r^3

Regular solid:

• Measure mass using a top pan balance
• Measure dimensions with a caliper or micrometer and then calculate volume by the correct equation (above)
• Divide mass by volume

Liquids:

• Measure the mass of an empty measuring cylinder
• Pour some of the liquid into it and measure the volume (use as much liquid to reduce percentage error)
• Measure the mass of the cylinder with liquid inside in order to calculate the mass of just the liquid
• Divide mass by volume

Irregular solid:

• Measure the mass
• Make a note of the amount of water in a measuring cylinder
• Immerse the object on a thread into liquid in the cylinder
• Note down the increase in level of the liquid, giving you the volume
• Divide mass by volume

Alloy = a solid mixture of two or more metals      (Using 'P' as 'density')

For an alloy with volume V, consisting of two metals A and B:

• Volume of metal A = Va
• Density of metal A = Pa
• Mass of metal A = PaVa

• Volume of metal B = Vb
• Density of metal B = Pb
• Mass of metal B = PbVb

Therefore, mass of alloy = PaVa + PbVb

And density = PaVa + PbVb

                                 V