What is the molarity of a solution and how is it calculated?

Molarity is a measure of the concentration of a solute in a solution, calculated by dividing the moles of solute by the volume of solution in litres.

Molarity, often denoted by the symbol 'M', is a unit of concentration used in chemistry. It is defined as the number of moles of solute (the substance being dissolved) per litre of solution. This gives a measure of how many moles of a substance are present in one litre of a solution, providing a way to compare the concentrations of different solutions.

To calculate molarity, you need to know two things: the number of moles of solute and the volume of the solution. The number of moles of solute is usually given in the problem or can be calculated from the mass of the solute and its molar mass. The volume of the solution is the total volume, not just the volume of the solvent. It is important to remember that the volume should be in litres. If the volume is given in millilitres, it must be converted to litres by dividing by 1000.

The formula for calculating molarity is:

Molarity (M) = Moles of solute / Volume of solution in litres

For example, if you have a solution containing 0.5 moles of sodium chloride (NaCl) in 2 litres of water, the molarity of the solution would be 0.5 moles / 2 litres = 0.25 M.

Understanding molarity is crucial in chemistry as it allows chemists to accurately measure and control the concentrations of substances in a solution. This is particularly important in reactions where the concentration of reactants can significantly affect the rate and outcome of the reaction.