Question

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

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

Answer 1

Answer: (B)

Given, mass of urea $=15 \,g$

Molar mass of urea $=60 \,g \,mor ^{-1}$

Volume $=500\, cm ^{3}=500\, mL =0.5 \,L $

$\begin{bmatrix}\because1\,cm^{3}=1\,mL\\ 1\,L=1000\,mL\end{bmatrix}$

$\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 $=\frac{15\, g }{60 \,g\, mor ^{-1} \times 0.5\, L }$

$\Rightarrow 0.5 \,mol / L =0.5 mol / dm ^{3}$

$\left(\because 1 L =1 \,dm ^{3}\right)$