electrolysis

• Electrolysis is the process by which ionic substances are broken down into simpler substances using electricity.
• During electrolysis, metals and gases may form at the electrodes.
• For electrolysis to work, the ions must be free to move. Ions are free to move when an ionic substance is dissolved in water or when melted (molten).
• If electricity is passed through molten lead (II) bromide, the lead bromide is broken down to form lead and bromine.
• The positive electrode, called the anode, will attract negatively charged non-metal ions.
• The negative electrode, called the cathode, will attract positively charged metal ions.
• The non-metal ions lose electrons to the anode (this is called oxidation) and are discharged as non-metal atoms which often combine to form molecules.

  e.g. 2Br- -> Br2 + 2e-
• The metal ions gain electrons from the cathode (this is called reduction) and are discharged as metal atoms.

  e.g. Pb(2+) + 2e- -> 2Pb
• Electrolyte labelling

  A) anode

  B) (positive)

  C) cathode

  D) negative

  E) reduction

  F) electron gain

  G) oxidation

  H) electron loss

  
• The electrodes are often made from graphite (carbon)
• The liquid that conducts electricity is called the electrolyte.
• When oxygen is not present, oxidation and reduction can be defined in terms of loss or gain of electrons
• Reduction - Gain of electrons
• Oxidation - Loss of electrons
• In electrolysis, the positive ion loses electrons at the cathode so it is reduced
• At the anode, the negative ion gains electrons to become neutral again so it is oxidised