Question

The molality of an urea solution in which $0.0100\, g$ of urea, $\left[\left( NH _2\right)_2 CO \right]$ is added to $0.3000\, dm ^3$ of water at STP is

• A. $0.555\, m$
• B. $5.55 \times 10^{-4} m$
• C. $33.3 \,m$
• D. $3.33 \times 10^{-2} m$

Answer 1

Answer: (B)

Molality $=\frac{\text { moles of solute }}{ kg \text { of water }}$
Moles of urea $=\frac{0.010}{60} mol$
Water at STP $\left( d =1\, g / cm ^3=1 \,kg / dm ^3\right)=0.3 \,dm ^3=0.3\, kg$
$\therefore$ Molality $=\frac{0.010}{60 \times 0.3}=5.55 \times 10^{-4} m$