Question

Molal depression constant for water is $ 1.86^{\circ}C $ The freezing point of a $ 0.05 $ molal solution of a non-electrolyte in water, is

• A. $ -1.86^{\circ}C $
• B. $ -0.93^{\circ}C $
• C. $ -0.093^{\circ}C$
• D. $ 0.93^{\circ}C $

Answer 1

Answer: (C)

Molal depression constant $k_{f}=1.86^{\circ} C$
Molality $=0.05 $
$\Rightarrow $ $\Delta T_{f}=k_{f} \times$ molality
$\Delta T_{f}=1.86 \times 0.05$
$\Delta T_{f}=0.093^{\circ} C $
$\Delta T_{f}=T_{1}-T_{2}$
where, $T_{1}=$ freezing point of solvent
$T_{2}$ = freezing point of solution
$T_{1}=0^{\circ} C$
$0.093=0-T_{2} T_{2}=-0.093$