CHEMICALS AND THE CHEMICALS AND THE EARTHEARTH

Electrolysis of brine (salty Electrolysis of brine (salty water)water)

Lesson objectivesLesson objectives

• To predict what will happen during To predict what will happen during the electrolysis of brinethe electrolysis of brine

• To see what happens during the To see what happens during the electrolysis of brineelectrolysis of brine

• To explain what happens during the To explain what happens during the electrolysis of brineelectrolysis of brine

• To know some of the uses of the To know some of the uses of the products of the electrolysis of brineproducts of the electrolysis of brine

Electrolysis of brineElectrolysis of brine

• When NaCl When NaCl dissolves in water, dissolves in water, it’s ions become it’s ions become free to move. free to move. So the So the solution can be solution can be electrolysed.electrolysed.

• In water some of In water some of the molecules of the molecules of water will naturally water will naturally split apart.split apart.

Electrolysis of brineElectrolysis of brine

• The NaCl will split into NaThe NaCl will split into Na++ ions and Cl ions and Cl-- ions.ions.

• Water splits into HWater splits into H++ ions and OH ions and OH- - (hydroxyl) (hydroxyl) ions.ions.

• So what do we think will happen during So what do we think will happen during electrolysis?electrolysis?

• Remember – Na is VERY reactive, it is Remember – Na is VERY reactive, it is much more likely to exist as an ion than much more likely to exist as an ion than hydrogen.hydrogen.

Now let’s see what Now let’s see what actually happensactually happens

Electrolysis of brineElectrolysis of brine

• The HThe H++ and Cl and Cl-- ions are discharged at ions are discharged at the electrodes.the electrodes.

Electrolysis of brineElectrolysis of brine

• HydrogenHydrogen comes off at the cathode comes off at the cathode ( - )( - )

• 2H2H++(aq)(aq) + 2e + 2e-- H H2(g)2(g)

• Hydrogen isHydrogen is …… …… oxidised or oxidised or reduced?reduced?

Electrolysis of brineElectrolysis of brine

• ChlorineChlorine comes off at the anode comes off at the anode ( + )( + )

• 2Cl2Cl(aq)(aq) - 2e - 2e-- Cl Cl2(g)2(g)

• Chlorine is ……Chlorine is …… oxidised or reduced?oxidised or reduced?

Electrolysis of brineElectrolysis of brine

• The NaThe Na++ and OH and OH- - ions stay in solution.ions stay in solution.

• They join together to form They join together to form sodium sodium hydroxidehydroxide..

• This is a very important alkaliThis is a very important alkali

Uses of the products of the Uses of the products of the electrolysis of brineelectrolysis of brine

HydrogenHydrogen

• Used to make Used to make margarinemargarine (helps to (helps to make the oils in the make the oils in the margarine spread on margarine spread on your bread)your bread)

• Used as a fuel Used as a fuel (already important in (already important in space rockets, but space rockets, but may be the fuel of may be the fuel of cars after the oil cars after the oil age)age)

Sodium hydroxideSodium hydroxide

• Detergents and Detergents and soapsoap

• PaperPaper

Sodium hydroxideSodium hydroxide

• Purifying bauxite to Purifying bauxite to extract aluminiumextract aluminium

• Rayon and acetate Rayon and acetate fibresfibres

ChlorineChlorine

• BleachBleach

• Killing bacteria in Killing bacteria in waterwater

ChlorineChlorine

• Solvents Solvents (used in (used in dry cleaning)dry cleaning)

• Hydrochloric acid Hydrochloric acid (HCl)(HCl)