JEE Main 2025 Jan 22 Shift 1, Chemistry Q17: Colligative Properties

JEE Main2025Jan 22, Shift 1Chemistry

Arrange the following solutions in order of their increasing boiling points.

(i) $1 0^{- 4}$ M NaCl (ii) $1 0^{- 4}$ M Urea

(iii) $1 0^{- 3}$ M NaCl (iv) $1 0^{- 2}$ M NaCl

Solution

Elevation of boiling point is a colligative property: $Δ T_{b} = i K_{b} m$ , so it scales with the effective particle concentration $i \cdot C$ .

For NaCl, $i = 2$ (ideal); for urea (non-electrolyte), $i = 1$ .

Effective concentrations: (i) $2 \times 1 0^{- 4}$ ; (ii) $1 \times 1 0^{- 4}$ ; (iii) $2 \times 1 0^{- 3}$ ; (iv) $2 \times 1 0^{- 2}$ .

Boiling-point order follows the same ranking: (ii) $<$ (i) $<$ (iii) $<$ (iv).

Concept behind this question

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