Why the blue color of copper sulfate solution in water changes to yellow when treated with concentrated hydrochloric acid?

The blue color of copper sulfate (CuSO4) solution is due to the presence of copper ions (Cu²⁺) in the solution. These copper ions absorb certain wavelengths of light and reflect others, resulting in the blue color that we observe. However, when copper sulfate solution is treated with concentrated hydrochloric acid (HCl), a chemical reaction occurs that leads to the formation of a different compound, which is yellow in color.

The reaction that takes place is as follows:

Copper sulfate (CuSO4) + Hydrochloric acid (HCl) → Copper chloride (CuCl2) + Sulfuric acid (H2SO4)

In this reaction, copper ions from copper sulfate react with chloride ions from hydrochloric acid to form copper chloride. Copper chloride is a yellowish compound, and its presence in the solution causes the color change from blue to yellow.

It's important to note that this color change is a result of the formation of a different chemical compound with different properties. The change in color is an indicator of the change in the chemical composition of the solution due to the reaction between copper sulfate and hydrochloric acid.