Question

$0.450g$ of urea $(mol.wt.60)$ in $22.5g$ of water show ${0.170}^{\circ }C$ of elevation in boiling point. The molal elevation constant of water is :

• A. ${0.052}^{\circ }C$
• B. ${0.51}^{\circ }C$
• C. ${5.1}^{\circ }C$
• D. ${0.83}^{\circ }C$

Answer 1

Answer: (B)

${0.51}^{\circ }C$

$△T=K_b\times \frac{w}{m}\times \frac{1000}{W}$
$0.170=K_b\times \frac{0.450}{60}\times \frac{1000}{22.5}$
$K_b=\frac{0.170\times 60\times 22.5}{1000\times 0.450}={0.51}^{\circ }C$