Solutions

Solutions

Question

If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, the change in freezing point of water (ΔTf), when 0.01 mol of sodium sulphate is dissolved in 1 kg of water, is (Kf = 1.86 K kg mol–1).

  • 0.0372 K

  • 0.0558 K

  • 0.0744 K

  • 0.0186 K

Answer

B.

0.0558 K

Na2SO4 → 2Na+  + SO42-
Van't Hoff factor of dissociation for Na2SO3 = 3
Molality of the solution = 0.01 m
ΔTf = i x Kf x m
= 3 x 1.86 x 0.01
 = 0.0558 K 

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