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The Periodic Table

The Alkali Metals  - Electrolysis of Sodium Chloride in Water (continued).

Questions.
1)  Where have the hydrogen H⁺ ions and hydroxide OH^- ions come from?
2)  Why don't the sodium Na⁺ ions and hydroxide ions
get discharged at the electrodes?

Answers.
1)  The ionisation of water produces hydrogen ions and hydroxide ions.
Although hydrogen ions are only present in small amounts
the reversible ionisation means that they are immediately replaced
when they are discharged at the cathode as hydrogen gas.
The water never runs out of hydrogen ions and hydroxide ions.

2)  Each electrode attracts two different ions.
The (-)cathode attracts both sodium Na⁺ ions and hydrogen H⁺ ions.
Only one type of ion at a time can be discharged at the electrode.
The ion discharged first is the one which is lower in the reactivity series.
Hydrogen is discharged leaving sodium Na⁺ ions in solution.

The (+)anode attracts both chloride Cl^- ions and hydroxide OH^- ions.
Chlorine is discharged leaving hydroxide OH^- ions in solution.
The solution therefore becomes sodium hydroxide_(aq).
Sodium hydroxide is used in the manufacture of paper, soap and ceramics.

See also the uses of hydrogen and the uses of chlorine.

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