Q1 / 120 · VITEEE 2015 · Chemistry
When copper is treated with a certain concentration of nitric acid, nitric oxide and nitrogen dioxide are liberated in equal volumes according to the equation,
$x \mathrm{Cu}+y \mathrm{HNO}_{3} \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{NO}$ $\quad+\mathrm{NO}_{2}+\mathrm{H}_{2} \mathrm{O}$
The coefficients of $x$ and $y$ are respectively
- A2 and 3
- Correct answerB2 and 6
- C1 and 3
- D3 and 8
Solution
Balanced equations are
$3 \mathrm{Cu}+8 \mathrm{HNO}_{3} \longrightarrow 3 \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}+2 \mathrm{NO}+4 \mathrm{H}_{2} \mathrm{O}$ ...(i)
$\mathrm{Cu}+4 \mathrm{HNO}_{3} \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}+2 \mathrm{NO}_{2}+2 \mathrm{H}_{2} \mathrm{O}$ ...(ii)
Here $\mathrm{NO}$ and $\mathrm{NO}_{2}$ are evolved in equal volumes, hence, on adding Eqs. (i) and (ii)
$\begin{aligned}
4 \mathrm{Cu}+12 \mathrm{HNO}_{3} & \longrightarrow 4 \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2} \\
&+2 \mathrm{NO}+2 \mathrm{NO}_{2}+6 \mathrm{H}_{2} \mathrm{O}
\end{aligned}$
or $2 \mathrm{Cu}+6 \mathrm{HNO}_{3}$
$\longrightarrow 2 \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{NO}+\mathrm{NO}_{2}+3 \mathrm{H}_{2} \mathrm{O}$
Hence, coefficients $x$ and $y$ of $C u$ and $\mathrm{HNO}_{3}$ are 2 and 6 respectively.
Hence, the correct answer is option: 'B'.