Question

On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue-green. Write the new compound formed.

Answer 1

Hint: Try to understand the use of hydrochloric acid in the above reaction. Find the oxidation state of copper in copper oxide to know if it can be oxidized or not. Hydrochloric acid acts as a chlorinating agent. It replaces oxygen with chlorine. However, you need to determine if the oxidation state of copper remains the same or it changes to find the correct compound.

Complete step-by-step answer:
Hydrochloric acid also called muriatic acid is a colorless, inorganic chemical substance having the formula HCl. Hydrochloric acid has a unique characteristic pungent smell.
It is classified as a strong acid and can easily attack the skin over a wide range, due to complete dissociation of the acid in water.
Hydrochloric acid is the simplest chlorine-based acid substance containing water. It is basically a solution of hydrogen chloride gas and water, and a variety of other chemical ions, like hydronium and chloride ions.
It is a naturally-occurring component of the gastric acid produced in the digestive systems of almost all animal species including humans.
In the above reaction, hydrochloric acid acts as a chlorinating agent and substitutes oxygen with chlorine in copper oxide. Copper exists in its maximum oxidation state and hence cannot be further oxidized. The reaction is given below:
$\text{2HCl + CuO}\to \text{ CuC}{{\text{l}}_{\text{2}}}\text{ + }{{\text{H}}_{\text{2}}}\text{O}$

The compound formed when hydrochloric acid reacts with copper oxide is copper(II) chloride.

Note: Hydrochloric acid is an important chemical used in various industries. For example:
- Production of polyvinyl chloride
- Descaling agent for domestic use
- Food additive for producing gelatin
- Processing of leather