Question

A solution of $x$ moles of sucrose in 100 grams of water freezes at $-0.2^\circ C$ . Calculate the amount of ice separate out when it is cooled upto $-0.25^\circ C$ :-

• A. $18\text{ grams }$
• B. $20\text{ grams }$
• C. $25\text{ grams }$
• D. $23\text{ grams }$

Answer 1

Answer: (B)

$\left(\left(ΔT\right)_{f}\right)_{I}=K_{f}\times m$
$0.2=1.86\times \frac{x}{100}\times 1000$
$x=\frac{0 . 2}{1 . 86 \times 10}=\frac{2}{186}mol$
$\left(\left(ΔT\right)_{f}\right)_{II}=1.86\times \frac{2 \times 1000}{186 \times W}$
$0.25=1.86\times \frac{2 \times 1000}{186 \times W}\Rightarrow W=\frac{2 \times 1000}{25}$
$W=80g$
Amount of ice seprated out $=100-80=20g$