5.29 describe the manufacture of sodium hydroxide and chlorine by the electrolysis of concentrated sodium chloride solution (brine) in a diaphragm cell

Positive electrode (anode):
Chloride ions lose electrons to form chlorine molecules

2Cl^- à Cl₂ + 2e^-

Negative electrode (cathode):

Water molecules gain electrons to form hydroxide ions and hydrogen molecules

2H₂O + 2e^- à 2OH^- + H₂

Overall equation:

2NaCl + 2H­₂O à 2NaOH + H₂ + Cl₂

The diaphragm keeps the sodium hydroxide and chlorine apart to stop them forming bleach.