A certain mass of a substance when dissolved in 100 g C 6 H 6 lowers the freezing point by 1.28°C . The same mass of solute dissolved in 100g of water lowers the freezing point by 1.40°C .If the s

Question

A certain mass of a substance when dissolved in $100 g C_{6} H_{6}$ lowers the freezing point by

1.28°C . The same mass of solute dissolved in 100g of water lowers the freezing point by 1.40°C .If the substance has normal molecular mass in benzene and is completely dissociated in water, into how many ions does it dissociate in water?

The $K_{f}$ for H₂O and C₆H₆ are $1.86 K m o l^{- 1} k g$ and $5.12 K m o l^{- 1} k g$ , respectively.

TestHub · Accepted Answer

Δ T f ​ = m × W 1000 × K f ​ × ω ​ 1.28 = M N ​ × 100 1000 × 5.12 × ω ​ . … ( i ) ( m N = normal molar mass) For the solution in water in which solute dissociate 1.40 = m l x p × 100 1000 × 1.86 × ω ​ . … ( ii ) ℓ = m e x p m N ​ = 1.28 1.40 ​ × 1.86 5.12 ​ = 3.01 ≃ 3 Now let formula of solute is A X ​ B Y ​ ⇌ x A + + y B − 1 - - 1 - ∞ x∞ y∞ i = 1 − ∞ + x ∞ + y ∞ i = 3 (Given ∞ = 1 ) No. of Ion given = ( x + y ) = 3

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