Question

3. Identify the following substances :

(ii) A dilute acid B which does not normally give hydrogen when reacted with metals but does give a gas when it reacts with copper.

Answer 1

Step 1: Nitric acid :${\mathrm{HNO}}_3$

Nitric acid does not usually react with metals but it gives Nitrogen dioxide ${\mathrm{NO}}_2$ when it reacts with copper metal. The following reaction is observed:

$$\begin{gathered} 4{\mathrm{HNO}}_3\left(\mathrm{l}\right)+\mathrm{Cu}\left(\mathrm{s}\right)\to \mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{s}\right)+2{\mathrm{NO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Nitric}\mathrm{acid}\mathrm{Copper}\mathrm{nitrate}\mathrm{Nitrogen}\mathrm{Dioxide} \end{gathered}$$

Step 2: Chemical inference:

1. Nitric oxide does not react with metals vigorously due to its oxidizing nature.
2. But with copper, it reacts to evolve Nitrogen dioxide gas, and copper nitrate is formed.

Final Answer: Hence, the answer is Nitric Acid.