Chemistry C2 Part Five

Revision PowerPoint - Big ideas

Electrochemistrymaking elements using

electricity

Electrolysis and ionic compounds• In electrolysis an electric current is passed through an ionic compound, either molten or in solution. • The compound breaks down into elements.

LEO the LION says GERrrr

• Oxidation happens at the positive electrode. Negative ions lose electrons. • Reduction happens at

the negative electrode. Positive ions gain electrons.

OXIDATION AND REDUCTIONLEO the lion says GERLosing Electrons is Oxidation, Gaining Electrons is Reduction.

Electrolysis in action

• The experiment uses a direct current• The electrodes allow

electrons to enter or leave the solution• The electrolyte is the

ionic compound

ElectroplatingMetal objects are electroplated by making them the negative electrode and placing them in a solution of soluble ions. e.g. nickel plating copper

Extracting aluminium• Aluminium is extracted by electrolysis of

molten bauxite dissolved in cryolite.

Brine and the chlor-alkali industry

The electrolysis of brine (salt water) produces sodium hydroxide, chlorine and hydrogen.Sodium

hydroxide is used to manufacture• soaps and

detergents• rayon and

acetate fibres• paper• ceramics

Chlorine is used to manufacture• antiseptics

and disinfectants

• pesticides and weed-killers

• bleachand to kill bacteria in drinking water

Hydrogen is used to manufacture• margarine• ammoniaIt is used in fuel cells and in rocket fuels for space craft

Electrolysis of brineChloride ions are discharged as chlorine gas at the +ve electrode. Hydrogen ions are discharged at the –ve electrode as hydrogen gas. Sodium and hydroxide ions are left as sodium hydroxide solution.