Question

Name the processes from which chlorine is obtained as a by-product. What will happen if an aqueous solution of NaCl is subjected to electrolysis?

Answer 1

In the electrolysis of molten NaCl, Cl₂ is obtained at the anode as a by product.

`NaCl_(("melt")) -> Na_(  ("melt"))^+ + Cl_(    ("melt"))^(-)`

At cathode: `Na_(   ("melt"))^+ e^(-) -> Na_((s))`

At anode : `Cl_(  ("melt"))^+ -> Cl_((g)) + e^(-)`

`2Cl_((g)) -> Cl_(2(g))`

The overall reaction is as follows:

If an aqueous solution of NaCl is electrolyzed, Cl₂ will be obtained at the anode but at the cathode, H₂will be obtained (instead of Na). This is because the standard reduction potential of Na (E°= − 2.71 V) is more negative than that of H₂O (E° = − 0.83 V). Hence, H₂O will get preference to get reduced at the cathode and as a result, H₂ is evolved.

`NaCl_( (aq)) -> Na_( (aq))^+ + Cl_((aq))^-`

At cathod: `2H_2O_((l)) + 2e^(-) -> H_(2(g)) + 2OH_((aq))^-`

At anode : `Cl_(("melt"))^(-) -> Cl_((g)) + e^(-)`

`2Cl_((g)) -> Cl_(2(g))`