Solutions and Colligative Properties - Result Question 10-1
10. Elevation in the boiling point for $1$ molal solution of glucose is $2$ K . The depression in the freezing point for $2$ molal solution of glucose in the same solvent is $2$ K . The relation between $K_b$ and $K_f$ is
(2019 Main, 10 Jan II)
(a) $K_b=1.5 K_f$
(b) $K_b=0.5 K_f$
(c) $K_b=K_f$
(d) $K_b=2 K_f$
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Answer:
Correct Answer: 10. (d)
Solution:
Elevation in boiling point $\left(\Delta T_b\right)=K_b \times m \times i$
Depression is freezing point $\left(\Delta T_f\right)=K_f \times m \times i$
where, $m=$ molality
For the glucose solution (van’t Hoff factor, $i=1$ ),
$ \Delta T_b^{1 m}=\Delta T_f^{2 m}=2 K $
So, $\quad K_b \times 1 \times 1=K_f \times 2 \times 1 \Rightarrow \quad K_b=2 K_f$
BETA
