Technician making a standard solution of copper (II) sulphate. A standard solution is one of a known and very precise concentration, which can then be used in accurate reactions and measurements. First, an exact amount of copper sulphate is weighed out. The molecular mass of copper sulphate is 159.62 grams/mole, and the scales read 15.962 when the final mass is present, meaning this is one tenth of a mole. This is then dissolved in a small amount of water, and the resulting solution added to a 200 millilitre volumetric flask. The flask is then carefully topped up until the bottom of the meniscus is exactly on the line. The resulting solution contains a tenth of a mole in a fifth of a litre of water, and therefore has a concentration of 0.5M (a molarity of half a mole per litre).