Question

The molarity of urea (molar mass $60\mathrm{g}\mathrm{mol}{}^{-1}$) solution by dissolving 15 g of urea in 500 $c{m}^3$ of water is

• A. $2\mathrm{mol}\mathrm{dm}{}^{-3}$
• B. $0.5\mathrm{mol}\mathrm{dm}{}^{-3}$
• C. $0.125\mathrm{mol}\mathrm{dm}{}^{-3}$
• D. $0.0005\mathrm{mol}\mathrm{dm}{}^{-3}$

Answer 1

Answer: (B)

Given, mass of urea $=15g$

Molar mass of urea $=60gmo{r}^{-1}$

Volume $=500c{m}^3=500mL=0.5L$

$\left[\begin{array}{c}\because 1c{m}^3=1mL\\ 1L=1000mL\end{array}\right]$

$\therefore$ Molarity

$=\frac{\text{ Mass of solute in grams }(W)}{\text{ Molar mass of solute }(M)\times \text{ Volume of solution }V(L)}$

Molarity of urea $=\frac{15g}{60gmo{r}^{-1}\times 0.5L}$

$\Rightarrow 0.5mol/L=0.5mol/d{m}^3$

$\left(\because 1L=1d{m}^3\right)$