Of the following four aqueous solutions, total number of those solutions whose freezing point is lower than that of $0.10 \mathrm{M} \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ is \_\_\_\_ (Integer answer) (A) $0.10 \mathrm{M} \mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}$ (B) $0.10 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}$ (C) 0.10 M KCl (D) $0.10 \mathrm{M} \mathrm{Li}_{3} \mathrm{PO}_{4}$

JEE Main · 2021 · 26 Aug 2021 · Shift 1 · Solutions

Of the following four aqueous solutions, total number of those solutions whose freezing point is lower than that of

0.10 M C_{2} H_{5} OH

is ____
(Integer answer)
(A)

0.10 M Ba_{3} (PO_{4})_{2}

(B)

0.10 M Na_{2} SO_{4}

0.10 M Li_{3} PO_{4}

Answer: 4

Solution

Depression of freezing point is

Δ T_{f} = i K_{f} m

, and ethanol is a non-electrolyte with

i = 1

, so any

0.10

M solution whose van't Hoff factor exceeds one freezes below it. On complete dissociation

B a_{3} (P O_{4})_{2}

gives five ions,

N a_{2} S O_{4}

three,

KCl

two and

L i_{3} P O_{4}

four. Every one of the four has

i > 1

at the same molar concentration, so the number of solutions freezing below the ethanol solution is

4

JEE Main · 2021 · 26 Aug 2021 · Shift 1 · Integer answer

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