Question

36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.

Answer 1

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

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

Step-1: Calculate the mass of the solution

Given, Mass of the sodium chloride (solute)= $36\mathrm{g}$

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= $36+100=136\mathrm{g}$

Step-2: Calculate the mass percentage $(\mathrm{m}/\mathrm{m})$ of sodium chloride 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 sodium chloride (solute)= $36\mathrm{g}$

Also, given, Mass of sodium chloride solution= $136\mathrm{g}$ (calculated in step-1)

Substituting the given values in the above formula

• Concentration of sodium chloride solution $(\mathrm{m}/\mathrm{m})\%=\frac{36}{136}\times 100$
• Concentration of sodium chloride solution $(\mathrm{m}/\mathrm{m})\%=\frac{3600}{136}$
• Concentration of sodium chloride solution $(\mathrm{m}/\mathrm{m})\%=26.47\%(\mathrm{m}/\mathrm{m})$