Question

Freezing point of urea solution is $−0.6^{∘}C$. How much urea $(m.wt.=60g/mol)$ will be required to dissolve in $3kg$ water ?
$\left(k_f=1.5^{∘}Ckgmo{l}^{−1}\right)$

• A. 24 g
• B. 36 g
• C. 60 g
• D. 72 g

Answer 1

Answer: (D)

$ΔT_f=\frac{k_f×1000×w}{M×W}$
$w=\frac{ΔT_f×M×W}{k_f×1000}$
$ΔT_f=0−(−0.6)=0.6^{∘}C$
$M=60g/mol$
$k_f=1.5^{∘}Ckgmo{l}^{−1}$
$W=3×10^{3}g$
$w=\frac{0.6×60×3×10^3}{1.5×1000}$
$=72g$