Question

The solubility of potassium chloride in water at 20 °C is 34.7 g in 100 g of water. The density of the solution is 1.3 g mL^-1. Calculate the concentration of potassium chloride in the solution in: % (m/m)

Answer 1

A solution comprises two parts i.e.; solute and solvent

• Solute: The component of the solution to be dissolved or the component present in the solution in a lesser quantity.
• Solvent: The component of the solution that dissolves or the component present in the solution in a larger quantity.
• Here, Potassium chloride $\left(\mathrm{KCl}\right)$ is the solute and the solvent is Water $\left({\mathrm{H}}_2\mathrm{O}\right)$.

Step-1: Calculate the mass of solvent

Given, Mass of the Potassium chloride (solute)= $34.7\mathrm{g}$

Also given, Mass of water (solvent)= $100\mathrm{g}$

• Mass of the solution= Mass of the solute+ Mass of the solvent
• Mass of the solution= $34.7+100=134.7\mathrm{g}$

Step-2: Calculate the mass percentage $(\mathrm{m}/\mathrm{m})$ of the solution

Formula to be used:

$\mathrm{Concentration}\mathrm{in}(\mathrm{m}/\mathrm{m})\%=\frac{\mathrm{Mass}\mathrm{of}\mathrm{the}\mathrm{solute}\left(\mathrm{g}\right)}{\mathrm{Mass}\mathrm{of}\mathrm{the}\mathrm{solution}\left(\mathrm{g}\right)}\times 100$

• $\mathrm{m}/\mathrm{m}$ represents mass by mass. It is a way to represent the concentration of the solution.
• It is defined as the mass of the solute in $\mathrm{g}$ dissolved in per $100\mathrm{g}$ of the solution.

Given, Mass of the Potassium chloride (solute)= $34.7\mathrm{g}$

Also given, Mass of solution= $134.7\mathrm{g}$ (calculated in Step-1)

Substituting the given values in the above formula

• Concentration of the Potassium chloride solution $(\mathrm{m}/\mathrm{m})\%=\frac{34.7}{134.7}\times 100$
• Concentration of the Potassium chloride solution $(\mathrm{m}/\mathrm{m})\%=\frac{3470}{134.7}$
• Concentration of the Potassium chloride solution $(\mathrm{m}/\mathrm{m})\%=25.76\%(\mathrm{m}/\mathrm{m})$