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  1. 1. Electrolysis the passage of a direct electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at electrodes and separation of materials. 08/03/14
  2. 2. Requirements of electrolysis 08/03/14 An electrolyte - It is a substance containing free ions which are the carriers of electric current in the electrolyte A direct current (DC) supply - It provides the electrical energy necessary to create or discharge the ions in the electrolyte. Electrical current is carried by electrons in the external circuit.
  3. 3. Requirements of electrolysis 08/03/14 Two electrodes - Electrode is an electrical conductor which provides the physical interface between the electrical circuit providing the energy and the electrolyte.
  4. 4. Requirements of electrolysis 08/03/14 The following figure shows the electrolyte, battery ( power supply) and electrodes ( cathode and anode ) required for electrolysis.
  5. 5. Electrolysis If you melt or dissolve an ionic compound (such as NaCl or CuCl2), then the ions become free to move around – and carry electrical current. Molecule of solid copper chloride CuCl2 (s) Molecule of solid copper chloride after being dissolved chloride ion Copper ion CuCl2 (aq) 08/03/14
  6. 6. Electrolysis Electrolysis is used to separate a metal from its compound. = chloride ion = copper ion 08/03/14
  7. 7. Purifying Copper Impure copper Solution containing copper ions + + Cu + Cu + Cu At the anode: Cu(s) Cu2+(aq) + 2e- 2+ --- 08/03/14 Pure copper 2+ 2+ At the cathode: Cu2+(aq) + 2e- Cu(s)
  8. 8. Electrolysis equations 08/03/14 We need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride): At the negative electrode the positive ions GAIN electrons to become neutral copper ATOMS. The half equation is: Cu2+ + 2e- Cu At the positive electrode the negative ions LOSE electrons to become neutral chlorine MOLECULES. The half equation is: 2 Cl- - 2e- Cl2
  9. 9. 08/03/14 Oxidation and Reduction in Electrolysis At the positive electrode the negative ions LOSE electrons –This is called Oxidation. The half equation is: At the negative electrode the positive ions GAIN electrons – this is called Reduction. The half equation is: 2Cl- - 2e- Cu2+ + 2e- Cl2 Cu
  10. 10. Electrolysis of brine 08/03/14 Sodium chloride (salt) is made of an alkali metal and a halogen. When it’s dissolved we call the solution “brine”, and we can electrolyse it to produce 3 things… Chlorine gas (Cl2) – used to kill bacteria and to make acids, bleach and plastics Hydrogen gas (H2) – used to manufacture ammonia and margarine Sodium chloride (brine) NaCl(aq) Positive electrode Negative electrode Sodium hydroxide (NaOH(aq)). Used to make soap, paper and ceramics
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