Question

Complete combustion of $1.80g$ of an oxygen containing compound $\left(C_x{H}_y{O}_z\right)$ gave $2.64g$ of $C{O}_2$ and $1.08g$ of $H_{2}O$. The percentage of oxygen in the organic compound is :

• A. $50.33$
• B. $53.33$
• C. $51.63$
• D. $63.53$

Answer 1

The correct option is B $53.33$

General reaction:
$C_x{H}_y{O}_z+(x+\frac{y}{4}-\frac{z}{2})O_2\to xC{O}_2+\frac{y}{2}{H}_{2}O$
From the above equation the relation for number of moles is:
$n_C=n_{C{O}_2}=\frac{2.64}{44}=0.06mol$

$n_H=2\times n_{H_{2}O}=\frac{1.08}{18}\times 2=0.12mol$

Mass of carbon, $m_C=\frac{2.64}{44}\times 12=0.72g$
Mass of hydrogen, $m_H=\frac{1.08}{18}\times 2=0.12g$
Mass of oxygen,
$m_O=\text{Mass of hydrocarbon}-m_C-m_H$
$=1.80-0.72-0.12=0.96g$
$\%O=\frac{0.96}{1.80}\times 100=53.33\%$

Hence the correct answer is option (b).