Elements P and Q form two types of non-volatile, non-ionizable compounds PQ and When 1 g of PQ is dissolved in 50 g of solvent ‘A’, was 0.689 K. . The molar masses of elements P and Q respectively, are: [2026]

Question

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’, ${ΔT}_{b}$ was 1.176 K while when 1 g of ${PQ}_{2}$ is dissolved in 50 g of solvent 'A', ${ΔT}_{b}$ was 0.689 K. $(K_{b} of ‘A’ = 5 {K kg mol}^{- 1})$ . The molar masses of elements P and Q $(in g mol⁻¹)$ respectively, are: [2026]

Smart Achievers · Accepted Answer

(4)

${(Δ T_{b})}_{P Q} = K_{b} m$

$1.176 = 5 \times \frac{1}{M_{1}} \times \frac{1000}{50}$

$M_{1} = 85.03$

${(Δ T_{b})}_{P Q_{2}} = 5 \times \frac{1}{M_{2}} \times \frac{1000}{50} = 0.689$

$M_{2} = 145.13$

$Let molar mass of P & Q are M_{P} and M_{Q} respectively$

$M_{P} + M_{Q} = 85.03$

$M_{P} + 2 M_{Q} = 145.13$

$M_{P} = 24.93 \approx 25$

$M_{Q} = 60.1 \approx 60$

Solution

1 65, 145

2 70, 110

3 60, 25

4 25, 60

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