Molar concentration, or molarity, or simply concentration, is a term in chemistry, and its physical chemistry branch. It measures the moles of solute in a given volume of a solution or mixture.
In chemistry, the molar concentration, is defined as the amount of a constituent (usually measured in moles – hence the name) divided by the volume of the mixture :
The volume in the definition refers to the volume of the solution, not the volume of the solvent. One litre of a solution usually contains either slightly more or slightly less than 1 litre of solvent because when a substance dissolves in a solvent it causes volume of liquid to increase or decrease.
The reciprocal quantity represents the dilution (volume) which can appear in Ostwald's law of dilution.