Question

Identify the substances oxidised and the substances reduced in the following reactions:
(i) 4Na(s) + O₂(g) -----> 2Na₂O(s)
(ii) CuO(s) + H₂(g) ------> Cu(s) + H₂O(I)

Answer 1

(i) In this reaction, sodium (Na) is changed into sodium oxide (Na₂O). This is the addition of oxygen to sodittm. Since addition of oxygen is called oxidation, therefore, the substance sodium (Na) is oxidised. 

Oxygen (O₂) is changed into Na₂O. Here, the addition of metal to oxygen takes place. So, the substance reduced is oxygen.
(ii) Here, copper oxide is reduced to copper metal whereas hydrogen is oxidised to water.