Density is an important property and is often used by chemists
to help identify substances. Density (d) is defined as the amount
of mass per unit volume. For example, water has a density of 1
gram per milliliter. This figure can be experessed as 1 g/mL or 1
g/cm^{3} since one cubic centimeter is the same volume as
one milliliter.

Definition:
Mass m
Density = ——————— or d = —
Volume V

To find the density of a sample, two measurements are
required. First, you must measure the mass. Second, you must
measure the volume. People often say that lead is heavy. What
they really mean is that lead is dense. For example, which is
heavier: a pound of lead or a pound of aluminum? This is a trick
question, if you are wondering. What if you have the same volume
of each metal? If you have exactly one mL (one cm^{3}) of
lead it will have a mass of 11.3 g. If you have the same volume
of aluminum it will have a mass of 2.7 g. So which one is more
dense?

Density is what determines whether a substance or an object
will float. If the density of the object is less than the density
of the liquid it will float. If the density of the object is
greater than the density of the liquid it will sink. Most types
of wood have a density less than the density of water so it
floats. Many metals have densities much greater than the density
of water. For example, iron has a density of 7.9 g/mL. So how is
it possible to make ships out of iron?

You have a chunk of aluminum
(Al) with a mass of 17.6 g and a
volume of 6.5 cm^{3}. What is the density of Al?

A cube of Al has a volume of 45.0 cm^{3} but you
have no lab balance. What is its mass?

Another piece of Al has a mass of 89.3 g but its volume is too
hard to measure. Calculate the volume of this piece of
Al.

Balsa wood is extremely
‘light’. A cubic meter of the wood has a mass of only
170 kg. What is the density of balsa wood in g/cm^{3}?
Does it float in water?

What is the mass of 4.56 ×
10^{9} mL of iron?

What volume of Pb has a mass of 4.0 kg?

How is it possible to make a ship out of iron actually float
in water?

Last updated: Sep 09, 2009
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