The depression in freezing point observed for a formic acid solution of concentration $0.5 \mathrm{~mL} \mathrm{~L}^{-1}$ is $0.0405^{\circ} \mathrm{C}$. Density of formic acid is $1.05 \mathrm{~g} \mathrm{~mL}^{-1}$. The Van't Hoff factor of the formic acid solution is nearly : (Given for vater $\left.\mathrm{k}_f=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$
Select the correct option:
A
0.8
B
1.1
C
1.9
D
2.4
✓ Correct! Well done.
✗ Incorrect. Try again or view the solution.
Solution
$[\text{HCOOH}] = 0.5\text{ ml l}^{-1}$$\Rightarrow (0.5\text{ ml} \times 1.05\text{ g ml}^{-1})\ \text{HCOOH in 1L}$$\Rightarrow 0.525\text{ g HCOOH in 1L}$$m = \frac{(0.525 / 46)}{1\text{kg}}\text{mol [Assuming dilute solution]}$$\therefore \Delta T_f = iK_fm \Rightarrow i = \frac{\Delta T_f}{K_fm} = \frac{0.0405 \times 46}{1.86 \times 0.525} = 1.9$
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