Question

when the powder of a metal is heated ina china dish it turns black but wen hydrogen is passed over it ,it regains its colour :-

a) what type of chemical reaction takes place in each of the two given steps

b)write balanced chamical equation for both reaction and name the metal whose powder is used.

Answer 1

a ) when copper (Cu) metal is heated in air, it reacts with the oxygen of air to form a black coloured compound, copper oxide.
Reaction can be written as -
2Cu + O₂$\stackrel{heat}{\to }$ 2CuO
​Here, in this reaction, copper is oxidised to copper oxide while oxygen is reduced to copper oxide. Thus, oxygen is the oxidising agent whereas copper is the reducing agent.
​
b) When hydrogen gas is passed over heated copper oxide, then black copper oxide is reduced and brown copper metal is formed.
CuO + H_​2 $\to$ Cu + H₂O
In this reaction, copper oxide is reduced to copper metal while hydrogen is oxidised to water.

These both reactions are oxidation and reduction reaction.