`CN^(ɵ)` is oxidised by a strong oxidising agent to `NO_3^(ɵ)` and `CO_2` or `CO_3^(2-)` depending upon the acidity of the reaction mixture. `HNO_3` a strong oxidising agent is reduced by a moderate reducing agent to NO. Write the balanced equation of `HNO_3` with KCN.
`CH^(ɵ)toCO_2+NO_3^(ɵ)`
`NO_3^(ɵ)NO`
If this reaction is carried out, what safety precautions are required?

Explanation

`(overset(-4)(C)overset(+3)(N))^(-2)orCN^(ɵ)toCO_2+NO_3^(ɵ)`
`C^(4-)+2H_2OtoCO_4+8e^(-)+4H^(o+)`
`underline(underset(x=3)(N^(3+))+3H_2Otounderset(x=5)(NO_3^(ɵ))+2e^(-)+6H^(o+))`
`underline(CN^(ɵ)+5H_2OtoCO_2+10^(o+)+NO_3^(ɵ)+10e^(-))` …. (i)
Reduction of `NO_3^(ɵ)` to `NO`:
`4H^(o+)+3e^(-)+undersetunderset(x=5)(x-6=-1)(NO_3^(o+))toundersetunderset(x=2)(x-2=0)(NO)+2H_2O+2H_2O` ....(ii)
Multiply equation (i) by 3 and equation (ii) by 10 and add them to get the final redox equation:
`underline(3CN^(ɵ)+10H^(o+)+7NO_3^(o+)to3CO_2+10NO+5H_2O)`
Acid `(H^(o+))` and `CN^(ɵ)` ion react to give `HCN`, a poisonous and deadly gas, unless the oxidising properties of the acid cause the oxidation of `CN^(ɵ)` before the HCN can escape.