Question

In the reactions gives below, identify the species undergoing oxidation and reduction: 

(i) H₂S(g) + Cl₂(g) → 2HCl(g) + S(s) 

(ii) 3Fe₃O₄(s) + 8Al(s) → 9Fe(s) + 4Al₂O₃(s) 

(iii) 2Na(s) + H₂(g) → 2NaH(s)

Answer 1

(i) H₂S(g) + Cl₂ → 2HCl(g) + S(s)

In this reaction, H₂S is oxidised because a more electronegative element i.e. chlorine is added to hydrogen (or a more electropositive element, hydrogen has been removed from S). Chlorine is reduced due to addition of hydrogen to it.

So, H₂S undergoes oxidation and Cl₂ undergoes reduction in this reaction.

(ii) 3Fe₃O₄(s) + 8 Al(s) → 9Fe(s) + 4Al₂O₃(s)

In this reaction aluminium is oxidation because oxygen is added to it. Ferrous ferric oxide (Fe₃O₄) is reduced because oxygen has been removed from it.

So, Al undergoes oxidation and Fe₃O₄ undergoes reduction in this reaction.

(iii) \(2\overset{o}{Na}(s)+\overset{o}{H_2}(g)\rightarrow2\overset{+1}{N}a\overset{-}{H}(s)\)

In this reaction, sodium is oxidised because oxidation number increases and H₂ is reduced because oxidation number decreases.

So, Na undergoes oxidation and H₂ undergoes reduction in this reaction.