Ncert Exercises & Solutions

8.8 While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions, ozone and nitric acid act only as oxidants. Why ?

In sulphur dioxide (

{SO}_{2}

), the oxidation number (O.N.) of S is +4 and the range of the O.N. that S can have is from +6 to –2.
Therefore,

{SO}_{2}

can act as an oxidising as well as a reducing agent. In hydrogen peroxide (

H_{2} O_{2}

), the O.N. of O is –1 and the range of the O.N. that O can have is from 0 to –2. O can sometimes also attain the oxidation numbers +1 and +2. Hence,

H_{2} O_{2}

can act as an oxidising as well as a reducing agent.
In ozone (

O_{3}

), the O.N. of O is zero and the range of the O.N. that O can have is from 0 to –2. Therefore, the O.N. of O can only decrease in this case. Hence, O3 acts only as an oxidant.
In nitric acid (

{HNO}_{3}

), the O.N. of N is +5 and the range of the O.N. that N can have is from +5 to –3. Therefore, the O.N. of N can only decrease in this case. Hence, HNO3 acts only as an oxidant.

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