Question

$10\, g$ of a mixture of $BaO$ and $CaO$ requires $100 \, cm^3$ of $2.5\, M\, HCl$ to react completely. The percentage of calcium oxide in the mixture is approximately (Given : molar mass of $BaO \,= \,153$)

• A. 55.1
• B. 47.4
• C. 52.6
• D. 44.9

Answer 1

Answer: (C)

52.6

Answer 2

Let, mass of $CaO =x g$
$\therefore$ Mass of $BaO =(10-x) g$

Again, $\because$ equivalent mass of BaO

$=\frac{\text { molar mass }}{2}=\frac{153}{2}=76.5$
$\therefore$ Number of moles of $BaO =\frac{10-x}{76.5}$

and $\because$ equivalent mass of $CaO =\frac{56}{2}=28$
$\therefore$ Number of moles of $CaO =\frac{X}{28}$

From molarity $=\frac{\text { moles of solute }}{\text { volume of solution (in L) }}$
$2.5=\frac{\text { moles of solute }}{\frac{100}{1000}}$
$\therefore$ Moles of solute $=\frac{2.5 \times 100}{1000}$

or $\frac{x}{28}+\frac{10-x}{76.5}=0.25$

or $76.5 x+28(10-x)=0.25 \times 28 \times 76.5$

or $48.5 x=255.5$

or $x=\frac{255.5}{48.5}=5.26$
$\therefore\%$ of $CaO =\frac{5.26}{10} \times 100=52.6 \%$