JEE Main · 2022 · 26 Jun 2022 · Shift 1 · Solutions

A 0.5 percent solution of potassium chloride was found to freeze at

- 0.2 4^{\circ} C

. The percentage dissociation of potassium chloride is ____. (Nearest integer)
(Molal depression constant for water is 1.80 K kg

mol^{- 1}

and molar mass of KCl is

74.6 g mol^{- 1}

)

Answer: 98

Solution

For a 0.5% solution: 0.5 g KCl in 99.5 g water (assuming 100 g total solution).

Molality:

m = \frac{0.5}{74.6} \times \frac{1000}{99.5} = 0.0673

mol/kg

Using

Δ T_{f} = i \times K_{f} \times m

0.24 = i \times 1.80 \times 0.0673

i = \frac{0.24}{1.80 \times 0.0673} = 1.98

For

KCl K X^{+} + Cl X^{-}

, van't Hoff factor

i = 1 + α (n - 1) = 1 + α (2 - 1) = 1 + α

1.98 = 1 + α

α = 0.98

Percentage dissociation = 98%

JEE Main · 2022 · 26 Jun 2022 · Shift 1 · Integer answer

Practise more: all JEE Main PYQs on Solutions →

More JEE Main questions on Solutions

Elements P and Q form two types of non-volatile, non-ionizable compounds PQ and $PQ_{2}$ . When 1 g of PQ is dissolved in 50 g of solvent 'A', $Δ T_{b}$ was 1.176 K while when 1 g of $PQ_{2}$ is dissolved in 50 g of solvent 'A', …
JEE Main 2026View solution →
Consider a solution of $CO_{2} (g)$ dissolved in water in a closed container.

Which one of the following plots correctly represents variation of log (partial pressure of CO2 in vapour phase above water) [y-axis] with log (mole fraction of $CO_{2}$ …
JEE Main 2026View solution →
Given below are two statements:

Statement I: The Henry's law constant $K_{H}$ is constant with respect to variations in solution's concentration over the range for which the solutions is ideally dilute.
Statement II : $K_{H}$ does not diff …
JEE Main 2026View solution →
The osmotic pressure of a living cell is 12 atm at 300 K. The strength of sodium chloride solution that is isotonic with the living cell at this temperature is $____$ $g L^{- 1}$ . (Nearest integer)

Given: …
JEE Main 2026View solution →
A substance 'X' (1.5 g) dissolved in 150 g of a solvent 'Y' (molar mass $= 300 g mol^{- 1}$ ) led to an elevation of the boiling point by 0.5 K. The relative lowering in the vapour pressure of the solvent 'Y' is $____$ $\times 1 0^{- 2}$ . (Nearest integer)
[Giv …
JEE Main 2026View solution →
Which one of the following graphs accurately represents the plot of partial pressure of $CS_{2}$ vs its mole fraction in a mixture of acetone and $CS_{2}$ at constant temperature ?
JEE Main 2026View solution →