Question

A mixture of hydrogen and oxygen $\left(45ml\right)$ is sparked to inform liquid water. The component not in excess reacts completely and $15m$ is left over. (All measurements are made at the same temperature and pressure). The composition by volume in the original mixture of $H_2:O_2$ is ___.

• A. $4:5$
• B. $7:2$
• C. either $4:5$ or $7:2$
• D. $2:1$

Answer 1

Answer: (C)

either $4:5$ or $7:2$

Case-1

Let us assume the excess is $H_2$.

$15$ mL of $H_2$ left over

Of the other $30mL$:

$20mL=H2$ ,and $10mL=O2$

Original mix was $35mL,H2$ and $10mL,O2$, that's a $\frac{7}{2}$ ratio

Case -2

Let us assume the excess is $O_2$.

$15mL$ of $O_2$ left over

Of the other $30mL$:

$20mL=H2$ and $10mL=O2$

Original mix was $20ml$ $H_2$ and $25mL$ $O_2$, that's a $\frac{4}{5}$ ratio