Which of the following solution has the highest freezing point?
Which of the following solution has the highest freezing point?
$0.1 \mathrm{~mol} \mathrm{KCl}$ in $1 \mathrm{~kg}$ water
$0.1 \mathrm{~mol} \mathrm{~K}_2 \mathrm{SO}_4$ in $1 \mathrm{~kg}$ water
$0.1 \mathrm{~mol}$ Urea in $1 \mathrm{~kg}$ water
$30 \mathrm{~g}$ of glucose in $1 \mathrm{~kg}$ water
Solution
Total no. of species will increases for the dissolution of strong electrohytes, $\mathrm{KCl}$ and $\mathrm{K}_2 \mathrm{SO}_4$.
$
\mathrm{KCl} \rightarrow \mathrm{K}^{+}+\mathrm{Cl}^{-} ; \mathrm{K}_2 \mathrm{SO}_4 \rightarrow 2 \mathrm{~K}^{+}+\mathrm{SO}_4^{2-}
$
Therefore, depression in freezing point will be in greater extent than undissociated organic compounds like urea and glucose is they don't dissociate in aqueous solution.
Now, $30 \mathrm{~g}$ of glucose $=\frac{30}{180}=\frac{4}{6}=0.167 \mathrm{~mol}$
Therefore, no. of moles of solute of glucose is greater than that of urea of $1 \mathrm{~kg}$ water. So, depression $\left(\Delta \mathrm{T}_{\mathrm{f}}\right)$ in freezing point is more than that of urea.
$
\Delta \mathrm{T}_{\mathrm{f}}=\operatorname{im} \mathrm{K}_{\mathrm{f}}
$
$\therefore \quad$ The highest freezing point is for $0.1 \mathrm{~mol} \mathrm{urea} \mathrm{in} 1 \mathrm{~kg}$ water