Aqueous solutions are assumed ideal…

Aqueous solutions are assumed ideal and strong electrolytes are completely dissociated. Take Kf(H2O)=1.86 K kg mol^-1 and R=0.0821 L atm K^-1mol^-1.

One or more options correct

Aqueous solutions are assumed ideal and strong electrolytes are completely dissociated. Take

K_f(\mathrm{H_2O})=1.86\ \mathrm{K\,kg\,mol^{-1}}

and

R=0.0821\ \mathrm{L\,atm\,K^{-1}mol^{-1}}

. Which of the following statement(s) is/are correct?

A. A $0.20\ \mathrm{m}$ aqueous glucose solution lowers the vapour pressure of water more than a $0.10\ \mathrm{m}$ aqueous $\mathrm{K_2SO_4}$ solution does
B. A $0.10\ \mathrm{m}$ solution of $\mathrm{K_4[Fe(CN)_6]}$ freezes at $-0.93\ ^\circ\mathrm{C}$
C. For a $0.10\ \mathrm{M}$ aqueous urea solution at $300\ \mathrm{K}$ , the osmotic pressure is $2.46\ \mathrm{atm}$
D. A $0.10\ \mathrm{m}$ urea solution and a $0.050\ \mathrm{m}$ $\mathrm{NaCl}$ solution have the same freezing point

Show answer and solution

Answer: B, C, D

Colligative properties depend on the total molality

i\,m

of solute particles. (A) is false: in dilute solution the vapour pressure lowering is proportional to the particle molality, which is

0.20

for the glucose solution but

3\times0.10=0.30

for

\mathrm{K_2SO_4}

(

i=3

), so the glucose solution lowers the vapour pressure less. (B) is true:

\mathrm{K_4[Fe(CN)_6]}

gives

5

ions, so

\Delta T_f=5\times1.86\times0.10=0.93\ \mathrm{K}

and the solution freezes at

-0.93\ ^\circ\mathrm{C}

. (C) is true:

\pi=CRT=0.10\times0.0821\times300=2.46\ \mathrm{atm}

. (D) is true:

0.050\ \mathrm{m}

\mathrm{NaCl}

gives

2\times0.050=0.10

particle molal, equal to that of

0.10\ \mathrm{m}

urea, so

\Delta T_f=0.186\ \mathrm{K}

in both.

Original question written in the JEE Advanced 2020 Paper 1 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake