Concentration in chemistry refers to the amount of a solute that is contained in a particular quantity of solvent or solution/04%3A_Reactions_in_Aqueous_Solution/4.05%3A_Concentration_of_Solutions). It is a measure of the abundance of a constituent divided by the total volume of a mixture. There are several types of mathematical descriptions of concentration, including mass concentration, molar concentration, number concentration, and volume concentration. Chemists use many different methods to define concentrations, some of which are described below:
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Molarity: The most common unit of concentration is molarity, which is defined as the number of moles of solute present in exactly 1 L of solution. It is, equivalently, the number of millimoles of solute present in exactly 1 mL of solution/04%3A_Reactions_in_Aqueous_Solution/4.05%3A_Concentration_of_Solutions).
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Normality: Normality is a concentration unit that defines concentration in terms of an equivalent, which is the amount of one chemical species that reacts stoichiometrically with another chemical species. It is no longer in common use, but it is helpful to understand its meaning.
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Mass per unit volume: This is a concentration unit that expresses the mass of a solute per unit volume of solution. It is commonly used when discussing how soluble a material is in water or a particular solvent.
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Parts per million/billion: These units express the concentration of a solute in terms of the number of parts of solute per million or billion parts of solution.
Knowing the concentration of solutes is important in controlling the stoichiometry of reactants for solution reactions/04%3A_Reactions_in_Aqueous_Solution/4.05%3A_Concentration_of_Solutions). Chemists use concentration to prepare solutions of known concentration by dissolving a known mass of solute in a solvent and diluting to a desired final volume or by diluting the appropriate volume of a more concentrated solution/04%3A_Reactions_in_Aqueous_Solution/4.05%3A_Concentration_of_Solutions).