Question

Pure water freezes at $273 \,K$ and $1$ bar. The addition of $34.5\, g$ of ethanol to $500\, g$ of water changes the freezing point of the solution. Use the freezing point depression constant of water as $2\,K\, kg\,mol^{-1}$. The figures shown below represent plots of vapour pressure (V.P.) versus temperature (T). [molecular weight of ethanol is $46\, g\,mol^{-1}$] Among the following, the option representing change in the freezing point is

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

Answer 2

$\Delta T _{ f }= K _{ f } \times m$
$=2 \times \frac{34.5 \times 2}{46}$
$=2 \times 1.5$
$=3$
Freezing point of ethanol $+$ water mixture
$=273-3=270$