Expression of Concentrations

Expression of Concentrations
The term 'per cent' or more usually the symbol '%' is used with one of four different meanings in the expression of concentrations according to circumstances. In order that the meaning to be attached to the expression in each instance is clear , the following notation is used:
Per cent w/w (% w/w) (percentage weight in weight) expresses the number of grams of solute in 100 g of product.
Per cent w/v (% w/v) (percentage weight in volume) expresses the number of grams of solute in 100 ml of product.
Per cent v/v (% v/v) (percentage volume in volume) expresses the number of millilitres of solute in 100 ml of product.
Per cent v/w (% v/w) (percentage volume in weight) expresses the number of millilitres of solute in 100 g of product.
Usually the strength of solutions of solids in liquids is expressed as percentage weight in volume, of liquids in liquids as percentage volume in volume and of gases in liquids as percentage weight in weight.
When the concentration of a solution is expressed as parts per million (p.p.m.), it means weight in weight, unless otherwise specified.
When the concentration of a solution is expressed as parts of dissolved substance in parts of the solution, it means parts by weight (g) of a solid in parts by volume (ml) of the final solution; or parts by volume (ml) of a liquid in parts by volume (ml) of the final solution; or parts by weight (g) of a gas in parts by weight (g) of the final solution.
When the concentration of a solution is expressed in molarity designated by the symbol M preceded by a number, it denotes the number of moles of the stated solute contained in sufficient Purified Water (unless otherwise stated) to produce 1 litre of solution.