Which one of the following reactions occur at the anode, in the Castner process of extracting sodium metal ?

Which one of the following reactions occur at the anode, in the Castner process of extracting sodium metal ?
  1. $\mathrm{H}_2 \longrightarrow 2 \mathrm{H}^{+}+2 e^{-}$
  2. $2 \mathrm{Cl}^{-} \longrightarrow \mathrm{Cl}_2+2 e^{-}$
  3. $4 \mathrm{OH}^{-} \longrightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2+4 e^{-}$
  4. $\mathrm{Na}^{+}+e^{-} \longrightarrow \mathrm{Na}$

Solution

In Castner process the process of extracting sodium metal can be written as, $4 \mathrm{NaOH} \longrightarrow 4 \mathrm{Na}^{+}+4 \mathrm{OH}^{-}$ Its oxidation reaction which occurs at anode is $4 \mathrm{OH}^{-} \longrightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2+4 e^{-}$

Asked in: AP EAMCET 2003

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