Dilution Formula

The property that the amount of solute does not change on dilution and concentration gives us a way to calculate what the new solution volume must be to get the desired concentration of the solute. We know that the molarity of a solution is defined as the number of moles per litre of solvent.

Molarity = (moles of solute) / (Volume of Solution in liters)

M = m / V

Now this equation can be re-written as follows:

Moles of Solute = Molarity × Volume of Solution

m = M × V

As the moles of solute remains the same in the solution during dilution as well as concentration, we can say that the number of moles in the solution before and after dilution remains the same. Let M₁ be the molarity of the original solution and V₁ be the volume of the original solution, M₂​ be the molarity and V₂ be the volume of the solution after dilution. As the number of moles remains constant:

M₁V₁ = M₂V₂

This equation is known as the dilution formula.

Note: In the above equation the volume of the solution before and after dilution should be in the same units.

The concentration of a solution depends upon the amount of solute present in the solution. The higher the amount of solute, the more concentrated is the solution. Dilution refers to a decrease in the concentration of a solution. It is generally done by increasing the content of the solvent in the solution. For example, adding more water to sugar syrup leads to a decrease in the concentration of the solution and the solution is said to be diluted.

Thus we can define dilution as:

Dilution is the process of decreasing the concentration of a solution by adding more solvent to it. Dilution may also be defined as the decrease in the pH of a chemical which may be solution, vapour or a gas. Concentration is the reverse of dilution.

Note that the amount of solute does not change in the dilution and concentration process. Only the amount of solvent changes.