Chemists use the mole so often to measure how much of a substance is present that it is convenient to have a name for the quantity which this unit measures. In the International System this quantity is called the amount of substance and is given the symbol n. Here again a common English word has been given a very specific scientific meaning. Although amount might refer to volume or mass in everyday speech, in chemistry it does not.
When a chemist asks what amount of H2O was added to a test tube, an answer like “0.0678 mol H2O” is expected. This would indicate that 0.0678 × 6.022 × 1023 or 4.08 × 1022, H2O molecules had been added to the test tube.
From ChemPRIME: 2.8: The Amount of Substance