Molarity
Concentration in moles of solute per litre of solution.
Formula
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Example
Dissolving 0.5 mol of salt in 2 L of water gives M = 0.5/2 = 0.25 mol/L.
How it works
Molarity tells you how many moles of a dissolved substance are present in each litre of the final solution. It works because concentration is measured as amount of solute spread through a total solution volume, so dividing moles by litres gives a standard way to compare solutions of different sizes. A higher molarity means more solute particles are packed into each litre of solution.
When to use it
Use this formula when you need to find the concentration of a solution in chemistry, especially in lab work, titrations, or when preparing solutions from a known amount of solute. It is also useful for converting between moles, volume, and concentration.
Worked example, step by step
A student dissolves 1.2 mol of glucose in 3.0 L of solution. M = n / V M = 1.2 / 3.0 M = 0.40 mol/L So the molarity of the glucose solution is 0.40 mol/L.
Common mistakes to avoid
- Using the volume of the solvent instead of the total volume of the solution
- Forgetting to convert millilitres to litres before calculating
- Mixing up moles with grams and plugging mass directly into the formula
Did You Know?
Molarity counts particles, not weight — one liter of 1 M solution holds 6×10²³ dissolved units.
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