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

2. 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?

3. Standard Volume The volume that we use is the litre. We do not call it a litre, we call it something else. 1 litre = 100 ml = 1000 cm 3 A cube that is 10 cm x 10 cm x 10 cm has a volume of 1000 cm 3 = 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 10 th person – a Roman idea). 1 litre = 1000 cm 3 = 1 decimetre

4. 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.