In an experiment, copper powder forms black CuO when heated in air. When H2 is passed over it on heating, reddish-brown copper is obtained again. Which is the correct explanation of these changes?
Answer and explanation
Correct answer: Copper is oxidised in the first step and CuO is reduced in the second step.
During the first step, copper combines with oxygen from air: 2Cu + O₂ → 2CuO. Addition of oxygen is oxidation, so copper is oxidised and the product becomes black CuO. In the second step, hydrogen reacts with CuO and removes its oxygen: CuO + H₂ → Cu + H₂O. Removal of oxygen is reduction, so option A correctly describes both changes; the other options ignore hydrogen’s role or misidentify the reaction.
Frequently asked questions
What is the correct answer to this question?
Copper is oxidised in the first step and CuO is reduced in the second step.
Why is this the correct answer?
During the first step, copper combines with oxygen from air: 2Cu + O₂ → 2CuO. Addition of oxygen is oxidation, so copper is oxidised and the product becomes black CuO. In the second step, hydrogen reacts with CuO and removes its oxygen: CuO + H₂ → Cu + H₂O. Removal of oxygen is reduction, so option A correctly describes both changes; the other options ignore hydrogen’s role or misidentify the reaction.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Chemical Reactions and Equations.
