Electrolysis of brine

—> during this, NaOH, H2 and CI2 all produced

—> NaOH = used in food processing and removing pollutants during paper manufacturing

—> H2 = using in production of HCI and as a fuel

—> CI2 = is a disinfectant and is also used in making plastics

—> when the NaCI is dissolved in water which ions are present?

• Na, CI- , H2, O+

—> CI2 is produced at the anode end

—> which atom/molecule is going to be discharged on the cathode?

• hydrogen

—> why?

• H+ = H2
• CI- = CI2
• Na+ & OH- = NaOH-

—> what is left behind?

• sodium

—> the gases are kept separate - prevent explosion due to heat/light.

—> chlorine can react with NaOH to make sodium chloride and sodium hypochlorate (bleach)

—> specialised cells are needed if the desired products are chlorine and sodium hydroxide

1. A diaphragm
2. A membrane cell

—> contains a diaphragm in the centre (porous mixture of asbestos and polymers)

—> brine added to one side and NaOH removed on the other

—> level of liquid on one side is more than the other - to prevent the brine from flowing back and mixing with the chlorine produced.

—> membrane is made from a polymer that only allows positive ions to pass through it.

—> Na ions pass through it but CI can’t

—> NaOH forms on the right hand side, preventing the NaCI from mixing with in

—> in both methods the CI2 will mix with any O2 produced at the anode, but can be purified by liquefying under pressure

—> under pressure, the oxygen will stay a gas

—> all atoms involved are present as ions in solution

—> H+ turns into H gas

• 2H+ (aq) + 2e- -> H2 (g)

—> CI- turns into CI gas

• 2CI- (aq) -> CI2 (g) + 2e-

—> Na+ and OH- form sodium hydroxide

• Na+ (aq) + OH- (aq) -> NaOH (aq)