Question

A solution containing $62\, g$ ethylene glycol in $250\, g$ of water is cooled to $-10^{\circ} C$. If $K _{ f }$ for water is $1.86\, K\, kg\, mol ^{-1}$, the amount of water separated as ice is______$g$

Answer 1

$\Delta T _{ f }= K _{ f } \times m =1.86 \times \frac{1}{0.25}$
$\therefore \Delta T _{ f }=7.44^{\circ} C$
Now, new freezing point is $-10^{\circ} C$.
$\therefore 10=1.86 \times \frac{1}{ W _{\text {water }}}$
$\therefore W _{\text {water }}=\frac{1.86}{10}=0.186\, kg =186\, g$
$\therefore $ mass of water separated as ice $=250-186$
$=64\, g$