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If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, the change in freezing point of water (\Delta T_{f}), when 0.01 mol of sodium sulphate is dissolved in 1 kg of water, is (K_{f}=1.86\, K\, kg\, mol^{-1})

  • Option 1)

    0.0186 K

  • Option 2)

    0.0372 K

  • Option 3)

    0.0558 K

  • Option 4)

    0.0744 K


Answers (1)


As we learnt in

Application of Vant Hoff factor -

(a)\: \: \: \left ( \frac{\Delta P}{P^{0}} \right )_{obs}= I_{solute}\times i

(b)\: \: \: \left ( \Delta T_{b} \right )_{obs}= K_{b}\times m\times i

(c)\: \: \: \left ( \Delta T_{f} \right )_{obs}= K_{f}\times m\times i

(d)\: \: \: \left ( \pi \right )_{obs}= C\times R\times T\times i



 \Delta T_{f}=K_{f}\times m\times i    (i for Na2SO4 is 3)

\Delta T_{f}=1.86\times0.01\times3

\Delta T_{f}=0.0558

Correct option is 3.


Option 1)

0.0186 K

This is an incorrect option.

Option 2)

0.0372 K

This is an incorrect option.

Option 3)

0.0558 K

This is the correct option.

Option 4)

0.0744 K

This is an incorrect option.

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