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)

${\left({\left(\Delta T\right)}_f\right)}_I=K_f\times m$
$0.2=1.86\times \frac{x}{100}\times 1000$
$x=\frac{0.2}{1.86\times 10}=\frac{2}{186}mol$
${\left({\left(\Delta T\right)}_f\right)}_{II}=1.86\times \frac{2\times 1000}{186\times W}$
$0.25=1.86\times \frac{2\times 1000}{186\times W}\Rightarrow W=\frac{2\times 1000}{25}$
$W=80g$
Amount of ice seprated out $=100-80=20g$