In chemistry, the molar concentration, c_{i} is defined as the amount of a constituent n_{i} (in moles) divided by the volume of the mixture V:

It is also called molarity (symbol M, in moles per liter). The volume in the definition refers to the volume of the solution, not the volume of the solvent, as one liter of a solution usually contains either slightly more or slightly less than 1 liter of solvent because the process of dissolution causes volume of liquid to increase or decrease.

### Units

The SI unit for molar concentration is mol/m3. However, more commonly the unit mol/L is used. A solution of concentration 1 mol/L is also denoted as "1 molar" (1 M).

1 mol/L = 1 mol/dm^{3} = 1 mol dm^{−3} = 1 M = 1000 mol/m^{3}

An SI prefix is often used to denote concentrations. Commonly used units are listed in the table hereafter:

### Applications of Molarity

To determine the molarity of a solution, the number of moles of solute added must be divided by the number of liters of total solution produced. If the amount of solute is given in grams, be sure to use the molar mass of the solute to determine the number of moles in order to determine the molarity.

For example, if there are 10 grams of salt (the solute) dissolved in enough water (the solvent) to produce 2L of the solution, what is the molarity of this solution?

When performing a chemical reaction, it is oftentimes simplifying to mix two solutions of known molarity, especially when one component is difficult to measure gravimetrically (by weighing). To determine the number of moles in a given solution of known molarity, simply multiply the molarity times the volume used, where V is the volume in liters.

For example, how many moles of potassium chloride (KCl) are in 4L of a 0.65M solution?

Using this same technique once can determine how much of an X molar solution will be required so that 1 equivalent (based on moles of atoms) of a reagent is added.

### Dilution (equation)

Dilution is a reduction in the concentration of a chemical (gas, vapor, solution). It is the process of reducing the concentration of a solute in solution, usually simply by mixing with more solvent. To dilute a solution means to add more solvent without the addition of more solute. The resulting solution is thoroughly mixed so as to ensure that all parts of the solution are identical.

Mathematically this relationship can be shown in the equation: c_{1}V_{1} = c_{2}V_{2} where c_{1} and c_{2} are the initial and final concentrations, respectively and V_{1} and V_{2} are the initial and final volumes of the solution.