Question

$15g$ urea and $20gNaOH$ dissolved in water. Total mass of solution is $250g$. Mole fraction of $NaOH$ in the mixture

• A. 0.036
• B. 0.62
• C. 0.5
• D. 0.4

Answer 1

Answer: (A)

mole fraction of $NaOH\Rightarrow \frac{\text{ moles of }NaOH}{\text{ moles of }NaOH+\text{ moles of urea }+\text{ moles of }{H}_{2}O}$
moles of $NaOH=\frac{w}{M_w}=\frac{20}{40}\Rightarrow \frac{1}{2}$
$[NaOH=23+16+1\Rightarrow 40]$
moles of urea $\Rightarrow \frac{w}{M_w}\Rightarrow \frac{15}{60}$
moles of $H_{2}O\Rightarrow \frac{w}{M_w}\Rightarrow \frac{215}{8}$

Mole fraction of $NaOH\Rightarrow \frac{\frac{1}{2}}{\frac{1}{2}+\frac{15}{60}+\frac{215}{18}}\Rightarrow 0.03$