JEE Main · 2022 · 26 Jul 2022 · Shift 2 · Solutions

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The elevation in boiling point for 1 molal solution of non-volatile solute A is 3 K . The depression in freezing point for 2 molal solution of A in the same solvent is 6 K . The ratio of

K_{b}

and

K_{f}

i.e.,

K_{b} / K_{f}

1 : X

. The value of X is [nearest integer]

Answer: 1

Solution

Using the colligative property relations:

Δ T_{b} = i K_{b} m_{1}

and

Δ T_{f} = i K_{f} m_{2}

For a non-volatile solute,

i = 1

\frac{Δ T _{b}}{Δ T _{f}} = \frac{K _{b} m _{1}}{K _{f} m _{2}}

\frac{3}{6} = \frac{K _{b} \times 1}{K _{f} \times 2}

\frac{1}{2} = \frac{K _{b}}{2 K _{f}}

\frac{K _{b}}{K _{f}} = \frac{1}{1}

Therefore,

X = 1

JEE Main · 2022 · 26 Jul 2022 · Shift 2 · Integer answer

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