Question

Black colour of copper oxide changes to bluish green if reacted with dilute hydrochloric acid. Why?

Answer 1

Dear Student,

Actually, Copper (II) oxide is soluble in HCl and makes Cu2+ and OH- ion. So, the reaction proceeds as:

CuO + 2HCl $\to$ CuCl₂ + H2O

The colour of copper oxide turns green because the cupric chloride solution absorbs red light and reflects green colour.

Regards