The freezing point depression constant for water is -1.86^ C m^ -1 . If 5.00 ~g Na SO_4 is dissolved in 45.0 ~g H_2 O , the freezing point is changed by -3.82^ C . Calculate the van't Hoff factor for Na_2 SO_4 .

Correct answer: A. 2.63 aligned Δ T_f & =i × K_f · m or i & = Δ T_f × W_ solvent K_f × n_ solute × 1000 & =(3.82 × 45)/(1.86 ×((5)/(142)) × 1000) & =2.63 aligned

NEET 2011

Exam: NEET
Year: 2011
Subject: Chemistry
Chapter: Solutions

NEET 2011 · Chemistry · Solutions

The freezing point depression constant for water is -1.86^ C m^ -1...

The freezing point depression constant for water is

-1.86^{\circ} \mathrm{C} \mathrm{m}^{-1}

. If

5.00 \mathrm{~g} \mathrm{Na} \mathrm{SO}_4

is dissolved in

45.0 \mathrm{~g} \mathrm{H}_2 \mathrm{O}

, the freezing point is changed by

-3.82^{\circ} \mathrm{C}

. Calculate the van't Hoff factor for

\mathrm{Na}_2 \mathrm{SO}_4

Options

A2.63
B3.11
C0.381
D2.05

Correct answer

A. 2.63

Step-by-step solution

\begin{aligned} \Delta T_f & =i \times K_f \cdot m \\ \text{\text{ or } } i & =\frac{\Delta T_f \times W_{\text{solvent }}}{K_f \times n_{\text{solute }} \times 1000}\\ & =\frac{3.82 \times 45}{1.86 \times\left(\frac{5}{142}\right) \times 1000}\\ & =2.63 \end{aligned}

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