Question

An aqueous solution containing 5% by mass of urea and 10% by mass of glucose. Calculate the freezing point if $K_f$ for $H_{2}O$ is $1.86Kmo{l}^{-1}kg$.

• A. $-{3.04}^{o}C$
• B. $-{6.24}^{o}C$
• C. $-{5.14}^{o}C$
• D. None of these

Answer 1

Answer: (A)

$-{3.04}^{o}C$

Solution has 5% by mass of urea and 10% by mass of glucose and therefore,
$w_{urea}=5g,w_{glucose}=10g,w_{H_{2}O}=85g$

$\Delta T=\Delta T_{urea}+\Delta T_{glucose}$

$\Delta T=\frac{1000\times 1.86\times 5}{60\times 85}+\frac{1000\times 1.86\times 10}{180\times 85}$

$=1.824+1.216=3.04$

$\therefore$ Freezing point of solution $=0-3.04=-{3.04}^{o}C$