Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.

Asked by Pragya Singh | 11 months ago |  62

##### Solution :-

The redox reaction is as given below:

$$Cl_{ 2 (s)} + SO_{ 2(aq)} \; + H_{ 2 }O_{(l)} \;$$

$$\rightarrow Cl^{ – }_{(aq)} + SO^{ 2- }_{ 4 (aq) }$$

The oxidation half reaction:

$$SO_{ 2 \;(aq)} \;\rightarrow \; SO^{ 2- }_{ 4 \; (aq) }$$

Add 2 electrons to balance the oxidation no. :

$$SO_{ 2 \;(aq)} \;\rightarrow \; SO^{ 2- }_{ 4 \; (aq) } \; + \; 2 \; e^{ – }$$

Add $$4 \; H^{ + }$$ ions to balance the charge:

$$SO_{ 2 \;(aq)} \;\rightarrow \; SO^{ 2- }_{ 4 \; (aq) } \; + \;4 \; H^{ + }_{ (aq) } \;+ \; 2 \; e^{ – }$$

Add $$2 H_{ 2 }O$$ to balance O atoms and $$H^{ + }$$ ions:

$$SO_{ 2 (aq)} + 2 H_{ 2 }O\rightarrow SO^{ 2- }_{ 4 (aq) }$$

$$+ 4 H^{ + }_{ (aq) } + 2 e^{ – }– —(1)$$

The reduction half reaction:

$$Cl_{2\;(s)} \; \rightarrow Cl^{-}_{(aq)}$$

Balance Cl atoms:

$$Cl_{ 2 \; (s) } \; \rightarrow \; 2 \; Cl^{ – }_{ (aq) }$$

Add 2 electrons to balance the oxidation no. :

$$Cl_{ 2 \; (s) } \; + \; 2 \; e^{ – } \rightarrow \; 2 \; Cl^{ – }_{ (aq) }——— (2)$$

Add equation (1) and (2) to get the balanced chemical equation:

$$Cl_{ 2 \; (s) }\; + \; SO_{ 2 \;(aq)} \; + \; 2 \; H_{ 2 }O_{ (l) } \;$$

$$\rightarrow \; 2 \; Cl^{ – }_{ (aq) } \; + \; SO^{ 2- }_{ 4 \; (aq) } \; + \; 4 \; H^{ + }_{ (aq) }$$

Answered by Pragya Singh | 11 months ago

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