Electricity and Chemistry

• Decomposition of an electrolyte with the help of electric current

• Electrolyte:

  • Aq. solution of ionic substance or molten ionic salt

  • Conducts electricity due to the presence of mobile ions

• Electrodes:

  • Rods which help current enter the electrolyte

  • Inert electrodes: do not take part in the reaction

  • Reactive electrodes: take part in the reaction

Principle#

Examples#

Electroplating#

• Coating one metallic object with another metal using electrolysis

• For electroplating, you need:

  • Anode made of metal you want to electroplate object with

  • Ions of same metal as anode in solution

  • Object to be plated at cathode

• Used to:

  • Make things look better

  • Prevent corrosion

Uses#

Refining Metals#

• This is purifying impure metals

• Rules:

  • Cathode: thin strip of pure metal

  • Anode: impure metal

  • Electrolyte: Aqueous Salt Solution of metal

• Example:

• Reaction at Anode: Cu -- 2e Cu^2+^ (mass decreases)

• Reaction at Cathode: Cu^2+^ + 2e Cu (mass increases)

Basics#

• Electrolysis is a way to decompose compounds, using electricity.

• Reduction of positive cations happens at the cathode

• Oxidation of negative anions happens at the anode

• For example:

  • At the anode: 2Cl^-^ → Cl~2~ + 2e^-^

  • At the cathode: 2H^+^ + 2e^-^ → H~2~

Extraction of Aluminium#

• The main ore of aluminium is bauxite -- high m.p.

• Aluminium (III) oxide (alumina) is dissolved in molten cryolite (Na~3~AlF~6~) -- this mixture has a lower m.p. (industrially preferred)

• During electrolysis aluminium is produced at the carbon cathode and oxygen at the carbon anode.

• Due to the high temp. the oxygen reacts with the graphite anode to form CO~2~ and so anode had to be periodically replaced

Electrolysis of Brine#

• Brine is concentrated NaCl solution

• Ions present: Na^+^, H^+^, Cl^-^ and OH^-^