Electrolysis

• Electrolysis 


  Diagram

  
• Electrolysis

  Splitting using electricity

  Conversion of ions into atoms by loss/gain of electrons
• Cell


  source of electrical energy
• Electrode


  Material connected to the positive and negative side of a cell

  Positive Anode Negative is Cathode
• Electrolyte


  A solution /molten substance which allows ions to move through it
• Anion


  Negative ions attracted to anode
• Cations

  Positive ions attracted to cathode
• Molten Lead Bromine - PbBr2


  Cathode: Pb2+ + 2e- - Pb (each Pb2+ ion gains 2 electrons to form lead atoms)

  Anode: 2Br- - Br2 + 2e- (each Br- ion loses 1 electron to form Br atoms: 2 Br atoms bond covalently - bromine molecule Br2)

  Overall: PbBr2 - Pb + Br2

  Lead Bromine - Lead + Bromine
• Aluminium oxide

  Overall: 2Al2O3 - 4Al + 302

  Cathode: Al3+ + 3e- - Al

  Anode: 2O2- - 02 + 4e-

  Aluminium oxide - Aluminium + oxygen

  Molten aluminium collects at bottom

  Solution of aluminium oxide in molten cryolite

  Steel tank lined with refractory bricks
• Aluminium Oxide


  Diagram

  
• Aluminium oxide

  Carbon anodes are replaced regularly as they react with the oxygen produced and burn to form CO2

  Molten cryolite reduces melting points - lowers operating temperature and less Co2 emissions and a lower melting point

  Cathode - each Al3+ ion gains 3 electrons to form Al atoms

  Anode - each O2- ion loses 2 electrons to form O2 atoms
• Electrolysis of water

  H2O(l) - H+(aq)+OH-(aq) - hydrogen and hydroxide

  Cathode: 2H+ + 2e- - H2

  Anode: 4OH- - 2H2O + O2 + 4e-

  Overall: 2H2O - 2H2 + O2

  In electrolysis of aqueous solutions, there are H and OH- atoms

  Cathode: If metal H+ ions are present, metal ions will stay in solution if more reactive than hydrogen - H2 gas made,if metal is less reactive, metal will form, Cu is less reactive than H2 so will always give Cu metal at cathode

  Anode - if OH- / halide ions are present (Br-,I-,Cl-) halogen molecules are formed (Br2,I2,Cl2), if no halide ions - O2 forms
• Electroplating


  Coating of metal using different metals via electrolysis

  To improve appearance

  To stop corrosion if metal is unreactive

  Anode - corrodes

  Cathode - solid coats metal
• RP

  1-Pour 50cm3 of solution in beaker

  2- Add lid and attach electrodes (not touching), attach crocodile clips to rod and connect said rod to red and black dc terminals of low voltage power supply - 4V

  
• Copper chloride half equations

  Cathode: Cu2+ + 2e- - Cu

  Anode: 2Cl- - Cl2 + 2e-
• Copper sulfate half equations

  Cathode: Cu2+ + 2e- - Cu

  Anode: 4OH- - 2H2O + O2 + 4e-
• Sodium chloride half equations

  Cathode: 2H+ + 2e- - H2

  Anode: 2Cl- - 2e- + Cl2
• Sodium sulfate half equations

  Cathode: 2H+ + 2e- - H2

  Anode: 4OH- - 2H20 + O2 + 4e-