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Tell me? The freezing point depression constant for water is -1.86°C m-1. If 5.00 g Na2SO4is dissolved in 45.0g H2O, the freezing point is changed by -3.82°C. Calculate the van't Hoff factor for Na2SO4.

The freezing point depression constant for water is -1.86°C m-1. If 5.00 g Na2SO4 is dissolved in 45.0g H2O, the freezing point is changed by -3.82°C. Calculate the van't Hoff factor for Na2SO4.

  • Option 1)

    2.05

  • Option 2)

    2.63

  • Option 3)

    3.11

  • Option 4)

    0.381

 
Answers (1)
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As we learned in concept

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

-

 

 K_{F}=\:-1.86\:^{o}C\:m^{-1}

m = \frac{5}{142\times 0.045}\:=\:0.782\:m

\therefore\:\Delta T=K_{F}\times m \times i

\Delta\:+3.82=\: +1.86\times 0.782\times i

\Delta i = 2.626 \sim 2.63

 


Option 1)

2.05

This option is incorrect.

Option 2)

2.63

This option is correct.

Option 3)

3.11

This option is incorrect.

Option 4)

0.381

This option is incorrect.

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