The greater the density, the more mass per unit volume.

The unit of density derived from SI units is kilograms per cubic meter, kg/m^{3} or kgm^{-3}.

More commonly, densities are given in g/mL (gmL^{-1}) or g/cm^{3} (gcm^{-3} or g/cc).

Density is a characteristic property of pure substances so density can help identify a particular pure substance.

Densities of Some Pure Substances

Pure Substance

State

Density (g/mL) at 25^{o}C and 1atm

gold

solid

19.3

mercury

liquid

13.6

lead

solid

11.4

silver

solid

10.5

copper

solid

9.0

zinc

solid

7.1

aluminium

solid

2.7

carbon (graphite)

solid

2.3

sulfur

solid

2.0

phosphorus

solid

1.8

ethanoic acid (acetic acid)

liquid

1.04

water

liquid

1.0

ethanol

liquid

0.79

chlorine

gas

0.0029

oxygen

gas

0.0013

In general metals are more dense than non-metals^{*}.

For example, at 25^{o}C the density of metallic lead is 11.4g/mL while the density of non-metallic sulfur is only 2.0g/mL.
The mass of 1mL of lead would be 11.4g, while the mass of 1mL of sulfur is only 2.0g

In general, solids are more dense than liquids which are more dense than gases^{**}.

For example, at 25^{o}C, solid sulfur has a density of 2.0g/mL, liquid water has a density of 1.0g/mL and gaseous oxygen has a density of 0.0013g/mL.

^{*} There are quite a few exceptions, especially the Group I (alkali metals) which have unusually low densities compared with other metals.
^{**}Note that mercury is an exception, it is a very dense liquid.

Density Calculations

density = mass ÷ volume

This equation can be re-arranged in order to calculate mass or volume given the density of a substance:

mass = density x volume

volume = mass ÷ density

Check for consistency in units:
If density is given in g/mL then the mass must be in grams and the volume in milliltres.
If the density is given in g/cm^{3} then the mass must be in grams and the volume in cubic centimetres.

Examples of Calculations Using Densities

Calculate the density of a ruby which has a volume of 1.6 cm^{3} and a mass of 6.7g.

density = mass ÷ volume
density = 6.7 ÷ 1.6 = 4.2 g/cm^{3}

Calculate the density of a liquid which has a volume of 28mL and a mass of 26.4g

density = mass ÷ volume
density = 26.4 ÷ 28 = 0.94 g/mL

Beeswax has a density of 0.96 g/cm^{3} at 25^{o}C and 1atm pressure.
Calculate the mass of 5 cm^{3} of beeswax.

density = mass ÷ volume
So mass = density x volume
mass = 0.96 x 5 = 4.8g

Milk has a density of 1.03 g/mL at 25^{o} and 1atm pressure.
Calculate the mass of 1L of milk.

density = mass ÷ volume
So mass = density x volume
Convert 1L to millilitres: volume = 1L x 1000mL/L = 1000mL
mass = 1.03g/mL x 1000mL = 1030g (=1.030kg)

At 25^{o} and 1atm pressure, diamond has a density of 3.5 g/cm^{3}.
Calculate the volume of 0.5g of diamond.

density = mass ÷ volume
So, volume = mass ÷ density
volume = 0.5g ÷ 3.5g/cm^{3} = 0.14cm^{3}

At 25^{o}C and 1atm pressure, ethylene glycol has a density of 1.11g/mL.
Calculate the volume of 0.025kg of ethylene glycol.

density = mass ÷ volume
So, volume = mass ÷ density
Convert 0.025kg to g: mass = 0.025kg x 1000g/kg = 25g
volume = 25g ÷ 1.11g/mL = 22.5mL