Question

During electrolysis of brine $H^{+}$ ions get discharged in preference to sodium ions. Give reason.

Answer 1

Because hydrogen is less reactive than sodium.

Brine is a concentrated salt solution, meaning that it is a liquid with lots of free ions in it. We have the ions from the salt, $N{a}^{+}$ and $C{l}^{-}$ and the ions from the water that the salt is dissolved in, $H^{+}$ and $O{H}^{-}$.

The positive ions (Hydrogen and sodium in this case) are attracted to the negative electrode (the cathode) due to having opposite charges. However, there is a rule at the negative electrode that the least reactive metal will be discharged (turned into atoms). Because hydrogen is less reactive than sodium, the hydrogen is discharged as $H$ atoms that then bind to form $H_2$ molecules.