NCERT Solution for Class 10 Science Chapter 1
Chemical Reactions and Equations
Intext Questions
Page No-13
Questions No-3
(i) 4Na(s) + O2(g) ® 2Na2O(s)
(ii) CuO(s) + H2(g) ® Cu(s) + H2O(l)
Identify the substances that are oxidised and the substances that are reduced in the following reactions.
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(i) Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.
(ii) Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H₂) gets oxidised to water (H₂O).
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(i) In this reaction sodium is combined with oxygen, i.e. gains oxygen and hence oxidized. Consequently oxygen is reduced.
(ii) In this reaction Hydrogen gains oxygen and forms water, hence it is oxidised. On the other hand copper loses oxygen and hence, reduced.
Analyze the oxidation and reduction that occur in the given reactions:
(i) 4Na(s)+O₂(g)→2Na₂O(s)
In this reaction:
» Oxidation: Na(s) → Na +(aq)+e −
» Reduction: O₂(g)+4e − →2O²− (aq)
(ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)
In this reaction:
» Oxidation: CuO(s) + H₂(g) → Cu(s) + H₂O(l)
» Alternatively, you can break it down into separate oxidation and reduction half-reactions:
» Oxidation: CuO(s) → Cu(s) +O²−
» Reduction: H₂ (g) +2H₂O + 4e− → 4OH −
In both reactions, the substance that loses electrons is oxidized, and the substance that gains electrons is reduced.