Question

Why brown colour copper powder on heating in air turns into black coloured substance?

Answer 1

When the copper is heated in the presence of Oxygen then it will result in the formation of copper oxide that is black in colour and basic in nature.

The basic chemical equation that is followed in the formation will be:

2Cu + O2 when heated will give 2CuO

However, if the hydrogen is passed through then it will turn brown.

Answer 2

Actual color of copper is brown.

Since, if heating this brown copper in air turns black in color this is because of formation of copper oxide.

This can be explained as copper reacts with oxygen present in air to form copper oxide, which is actually black in color.