Chemistry - Liquid Solution Question with Solution | TestHub

$\begin{array}{rl}\because \Delta T_f& =k_f\times \text{ Molality of solution }\\ \Delta T_b& =k_b\times \text{ Molality of solution }\end{array}$ or $\frac{\Delta T_f}{\Delta T_b}=\frac{k_f}{k_b}$ Given that $\Delta T_b=T_2-T_1=100.18-100=0.18$ $\begin{array}{rl}& k_f\text{ for water }=1.86\mathrm{K}\mathrm{kg}{\mathrm{mol}}^{-1}\\ & k_b\text{ for water }=0.512\mathrm{K}\mathrm{kg}{\mathrm{mol}}^{-1}\end{array}$ $\therefore \frac{\Delta T_f}{0.18}=\frac{1.86}{0.512}$ $\begin{array}{rl}\Delta T_f& =\frac{1.86\times 0.18}{0.512}\\ & =0.6539\sim 0.654\\ \Delta T_f& =T_1-T_2\\ 0.654& =0^{\circ }\mathrm{C}-T_2\end{array}$ $\therefore T_2=-0.654^{\circ }\mathrm{C}$ ($T_2\to$ Freezing point of aqueous urea solution)