Learning Objectives:• To understand the units of concentration (mol.dm-3)

Units of Concentration

Amount and Volume

The measure of the amount of a substance that we use is: the number of moles

The other important thing we need to know is:

what is the volume of water into which the substance is dissolved?

Standard VolumeThe volume that we use is the litre. We do not call it a litre, we call it something else.

1 litre = 100 ml = 1000 cm3

A cube that is 10 cm x 10 cm x 10 cm has a volume of 1000 cm3 = 1 litre

10 cm is also known as a decimetre. (a decathlon has 10 events; a decagon has 10 sides; to decimate is to kill every 10th person – a Roman idea).

1 litre = 1000 cm3 = 1 decimetre

mol.dm-3

The unit that we use to explain how much of a substance is dissolved in a given volume is:

moles per decimetre cubed or mol.dm-3

You will always refer to concentrations using this unit.

e.g., You might use a 0.2 mol.dm-3 solution of hydrochloric acid in an experiment.