Moles. A balloon, a flask and a beaker, each containing one mole of a substance. One mole is a quantity used to compare mass and volume. It is defined as the number of atoms in exactly 12 grams of carbon-12, equivalent to 6.02 x 10^23 atoms. One mole of a compound contains that number of its basic units. The balloon contains one mole of a gas. The beaker contains one mole of a crystalline salt and the flask contains one mole of copper (II) sulphate in one litre of water ( a one molar solution).