Electrolysis

• Setup


  Electrolysis typically takes place in an electrolytic cell, which consists of two electrodes (usually made of inert materials like graphite or platinum) immersed in an electrolyte (a liquid or molten substance that conducts electricity)
• Electrodes


  The electrodes are connected to a direct current (DC) power supply. The electrode connected to the positive terminal of the power supply is called the anode, and the electrode connected to the negative terminal is called the cathode.
• Electrolysis


  The passage of a direct electric current through an ionic solution
• Electrolyte


  Solution containing ions
• Anode


  Positive electrode
• Cathode


  Negative electrode
• Cation


  Positively charged ion
• Anion


  Negatively charged ion
• Oxidation


  Loss of electrons
• Reduction

  Gain of electrons
• Electrolysis of molten NaCl

  1. Positive anode

  2. Negative cathode

  3. Na+ at cathode

  4. Cl- at anode

  5. Cl2 produced at anode

  6. Na produced at cathode
• Opposites attract in electrolysis of molten NaCl
• Electrolysis of aqueous NaCl

  1. Positive anode

  2. Negative cathode

  3. Cl- at anode

  4. Na+ at cathode

  5. Cl2 produced at anode

  6. H2 produced at cathode
• At the cathode, the least reactive element is produced. (There are only 4 metals less reactive than hydrogen. These are Cu, Ag, Au, Pt)
• At the anode, a halogen is produced otherwise oxygen is produced
• Anions that can go to the anode

  • OH- and Cl-
• Cl- is the anion that will go to the anode
• Electrolysis of aqueous NaCl - anode

  1. Cl2 produced

  2. 2Cl- -> Cl2 + 2e-
• Electrolysis of aqueous NaCl - anode (if oxygen is produced)

  1. O2 produced

  2. 4OH- -> O2 + 2H2O + 4e-
• Cations that can go to the cathode

  • Na+ and H+
• H+ is the cation that will go to the cathode
• Electrolysis of aqueous NaCl - cathode

  1. H2 produced

  2. 2H+ + 2e- -> H2
• Electroplating


  In electroplating the anode becomes part of the reaction taking place
• Electroplating - anode


  Ag -> Ag+ + e-
• Cations travel to the cathode because they are attracted to the negative electrode
• Electroplating - cathode


  Ag+ + e- -> Ag