Question

What is the boiling point for a $0.743m$ aqueous solution of $KCl$ ?

Answer 1

The temperature at which a liquid's vapour pressure equals the pressure surrounding the liquid, and the liquid turns into a vapour is known as the boiling point of a material. The surrounding air pressure has an effect on a liquid's boiling point.

Complete answer:
We are using the formula,
$\Delta {T_b} = {T_b} - T_b^ * = i{K_b}m$
Where,
$\Delta {T_b}$ is the change in boiling point in $^\circ C$ from the pure solvent $T_b^ *$ to the solution ${T_b}$ .
$i$ is the Van't Hoff factor, or an effective number of solute particles in solution. The Van't Hoff factor is ratio of the observed colligative property to the calculated colligative property.
${K_b} = 0.512^\circ C/m$ is the boiling point constant of the water.
$m$ is the molality of the solution.
Here we are assuming $100\%$ dissociation of $KCl$ .
The chemical reaction equation of $KCl$ is given as:
$KCl\left( {aq} \right) \to {K^ + }\left( {aq} \right) + C{l^ - }\left( {aq} \right)$
We can find that the effective number of solute particles $i \approx 1 + 1$ .
Therefore,
${T_b} - T_b^ * = i{K_b}m$
That is, ${T_b} = T_b^ * + i{K_b}m$
After substituting the values, we got
${T_b} = 100^\circ C + 2 \times 0.512^\circ C/m \times 0.743m$
${T_b} = 100.761^\circ C$
Hence, the boiling point of the aqueous solution is $100.761^\circ C$ .

Additional Information:
Remember the formula, $\Delta {T_b} = {T_b} - T_b^ * = i{K_b}m$ . Keep in mind that when another compound is applied to a liquid, that is, a solvent, the boiling point of the liquid increases, implying that a solution has a higher boiling point than a pure solvent.

Note:
The Van 't Hoff factor, $i$ is a measurement of a solute's effect on colligative properties like osmotic pressure, relative vapour pressure reduction, boiling-point elevation, and freezing-point depression. The ratio between the real concentration of particles formed when a substance is dissolved, and the concentration of a substance measured from its mass is known as the Van 't Hoff factor.