Question

A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black color product. Identify M and black colored product and also explain the reaction of M with oxygen.

Answer 1

Reaction of Copper with Acid:

• Copper $\left(\mathrm{Cu}\right)$ lies below hydrogen in the reactivity series. Thus it will not react with Sulfuric acid or Hydrochloric acid and hence there will be no evolution of Hydrogen$\left({\mathrm{H}}_2\right)$ gas.
• $\underset{\mathrm{Copper}}{\mathrm{Cu}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \mathrm{No}\mathrm{reaction}$

Reaction of Copper with Oxygen:

• The reaction of Copper$\left(\mathrm{Cu}\right)$ with oxygen$\left({\mathrm{O}}_2\right)$ produces a black-colored copper oxide $\left(\mathrm{CuO}\right)$.
• The chemical reaction can be depicted as:

$2\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{CuO}\left(\mathrm{s}\right)$

• It is an example of a combination reaction.

Hence, M is Copper and the black-colored product is Copper oxide.