Molarity

In-depth explanation of Molarity

Molarity is the concentration of a solution expressed as moles of solute per litre of solution, M = mol solute / L solution. It is the most common concentration unit in laboratory chemistry because it links directly to stoichiometry through moles = M × V. Molarity depends on temperature because the volume of a solution changes with temperature, even though the amount of solute stays the same. Because molarity uses the volume of the solution rather than the solvent, it must be defined carefully when mixing solutions. Preparing a solution of known molarity involves dissolving the solute and diluting it to the mark on a volumetric flask.

Going deeper: Molarity

Key ideas: Formulas: M = n/V, n = M V, grams = M V times molar mass. Convert from mass percent with M = (10 x percent x density in g/mL) / molar mass. Dilution uses M1V1 = M2V2. Concentrations of ions follow stoichiometry: 0.1 M CaCl2 gives 0.1 M Ca2+ and 0.2 M Cl-.

Common mistakes and connections: Typical errors are using the solvent volume rather than total solution volume, and using mL in place of L. Another is forgetting the multiple ions released by an ionic compound. The molarity of a solution changes with temperature as it expands. Links to dilution, titration, stoichiometry and normality.

Visualization of Molarity

Molarity is mol solute per litre of solution; concentrated HCl is about 12 M while typical lab solutions are 0.1 to 2 M. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Dissolving 5.85 g of sodium chloride (0.100 mol) in enough water to make 1.00 L gives a solution of 0.100 M.

Where Molarity fits in States of Matter & Solutions

Molarity is topic 76 of 109 in States of Matter & Solutions.

Related topics

• SolubilityBeginner
• Saturated Unsaturated SupersaturatedBeginner
• Like Dissolves LikeBeginner
• MolalityIntermediate
• Mass PercentBeginner
• Parts Per MillionBeginner

Browse all 109 topics in States of Matter & Solutions