Question

Which one of the following has minimum freezing point ?

• A. $0.1\,M\,NH_{4}Cl$
• B. $0.1\,M\,BaSO_{4}$
• C. $0.1\,M\,Al_{2}\left(SO_{4}\right)_{3}$
• D. $0.1\,M\,K_{2}Cr_{2}O_{7}$

Answer 1

Answer: (C)

$0.1\,M\,Al_{2}\left(SO_{4}\right)_{3}$

Answer 2

Depression in freezing point $\propto$ no. of particles in the solution $\begin{matrix}&NH_{4}Cl&BaSO_{4}&K_{2}Cr_{2}O_{7}&Al_{2}\left(SO_{4}\right)_{3}\\\ {\text{No. of particles}}&2&2&3&5\end{matrix}$ The depression in freezing points $(\Delta T_f)$ will be in the order; $NH_4Cl = BaSO_4 < K_2Cr_2O_7 < Al_2(SO_4)_3$ Thus, $Al_2(SO_4)_3$ will have maximum depression in freezing point i.e., its actual freezing point will be minimum.