Amount of substance and molar mass – fundamentals and applications
How it works
The amount of substance n is a fundamental quantity in chemistry. It is used to describe how many particles are contained in a sample of a substance. The unit of amount of substance is mole (mol). One mole corresponds to 6.022 · 10^23 particles (Avogadro's number). The molar mass M indicates what mass 1 mol of a substance has; its unit is g/mol. It is obtained by adding the atomic masses of all atoms contained in the formula. Thus, the mass m of a substance is related to the amount of substance n and the molar mass M by the relation n = m / M. Conversely, m = n · M. These relationships help to compare samples of substances and to calculate chemical reactions.
The amount of substance n of a substance is calculated by dividing the mass m of the substance by its molar mass M: n = m / M. The molar mass M is obtained from the sum of the atomic masses of all atoms in the chemical formula of the substance.
An example
What is the amount of substance of 18 g of water (H₂O)? The molar mass of water is 18 g/mol.
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50 Exercises
To the learning unit →Own explanation and own practice exercises by AmyMath. Subject reference framework: Chemistry. The topic assignment may vary by federal state.