Question

Give reasons for the following.
Elevation of boiling point of $1$M KCl solution is nearly double than that of $1$M sugar solution.

Answer 1

Elevation of boiling point is a colligative property and depends on the number of solute particles. Both KCl and sugar solution has the same molarity. But the van't Hoff factor for KCl is twice that for sugar. Hence, the elevation of the boiling point of 1M KCl solution is nearly double that of 1M sugar solution.

$\Delta T_b=i{K}_{b}m$

$\Delta T_b\propto i$

Note: Sugar is non-electrolyte and does not dissociate in water. Hence, it has van't Hoff factor of 1. KCl is an electrolyte and dissociates in water. 1 molecule of KCl gives 2 ions. $KCl\to K^{+}+C{l}^{-}.$ Hence, it has van't Hoff factor of 2.