1. REDOX A guide for National 4 and 5 students KNOCKHARDY PUBLISHING

2. INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at National 4 and National 5 Chemistry. It is based on the requirements of the SQA specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of chemistry topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING REDOX

3. CONTENTS Definitions of oxidation and reduction Redox reactions Balancing ionic half equations Combining half equations to form a redox equation REDOX

4. Before you start it would be helpful to… Recall the layout of the periodic table Be able to balance simple equations REDOX

5. OXIDATION GAIN OF OXYGEN 2Mg + O 2 ——> 2MgO magnesium has been oxidised as it has gained oxygen REMOVAL (LOSS) OF HYDROGEN C 2 H 5 OH ——> CH 3 CHO + H 2 ethanol has been oxidised as it has ‘lost’ hydrogen OXIDATION & REDUCTION - Definitions

6. REDUCTION GAIN OF HYDROGEN C 2 H 4 + H 2 ——> C 2 H 6 ethene has been reduced as it has gained hydrogen REMOVAL (LOSS) OF OXYGEN CuO + H 2 ——> Cu + H 2 O copper(II) oxide has been reduced as it has ‘lost’ oxygen However as chemistry became more sophisticated, it was realised that another definition was required

7. ... OXIDATION Removal (loss) of electrons‘OIL’ species will get less negative or more positive REDUCTION Gain of electrons‘RIG’ species will become more negative or less positive REDOX When reduction and oxidation take place OXIDATION AND REDUCTION IN TERMS OF ELECTRONS Oxidation and reduction are not only defined as changes in O and H OXIDATION & REDUCTION - Definitions

8. ... OXIDATION Removal (loss) of electrons‘OIL’ species will get less negative or more positive REDUCTION Gain of electrons‘RIG’ species will become more negative or less positive REDOX When reduction and oxidation take place OXIDATION AND REDUCTION IN TERMS OF ELECTRONS Oxidation and reduction are not only defined as changes in O and H OXIDATION & REDUCTION - Definitions OIL - Oxidation Is the Loss of electrons RIG - Reduction Is the Gain of electrons

9. REDOXWhen reduction and oxidation take place OXIDATION Removal (loss) of electrons ‘OIL’ species will get less negative or more positive REDUCTIONGain of electrons ‘RIG’ species will become more negative or less positive REDOX REACTIONS OXIDATION AND REDUCTION IN TERMS OF ELECTRONS Oxidation and reduction are not only defined as changes in O and H

10. REDOXWhen reduction and oxidation take place OXIDATION Removal (loss) of electrons ‘OIL’ species will get less negative or more positive REDUCTIONGain of electrons ‘RIG’ species will become more negative or less positive REDUCTION in O.S. Species has been REDUCED e.g. Cl is reduced to Cl¯ (0 to -1) INCREASE in O.S. Species has been OXIDISED e.g. Na is oxidised to Na + (0 to +1) REDOX REACTIONS OXIDATION AND REDUCTION IN TERMS OF ELECTRONS Oxidation and reduction are not only defined as changes in O and H

11. REDUCTION in O.S. INCREASE in O.S. Species has been REDUCED Species has been OXIDISED REDOX REACTIONS OXIDATION AND REDUCTION IN TERMS OF ELECTRONS Q. State if the changes involve oxidation (O) or reduction (R) Fe 2+  Fe 3+ + e - I 2 + 2e -  2I - Mg  Mg 2+ + 2e - 2Cl -  Cl 2 + 2e - Al 3+ + 3e -  Al 3+

12. REDOX REACTIONS REDUCTION in O.S. INCREASE in O.S. Species has been REDUCED Species has been OXIDISED OXIDATION AND REDUCTION IN TERMS OF ELECTRONS Q. State if the changes involve oxidation (O) or reduction (R) or neither (N) Fe 2+  Fe 3+ + e - O I 2 + 2e -  2I - R Mg  Mg 2+ + 2e - O 2Cl -  Cl 2 + 2e - O Al 3+ + 3e -  AlR

13. REDOX REACTIONS Any reaction which involves reduction must also involve oxidation because these processes do not happen alone The name given to reactions involving both reduction and oxidation is redox reactions 2 Na 2 Na + + 2 e - Cl 2 + 2 e - 2 Cl - oxidation reduction redox 2 Na + Cl 2 2 Na + Cl - At National 5 level you will come across REDOX in the topics extraction of metals from their ores and electrochemical cells

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15. WELL DONE! Try some past paper questions

16. REDOX THE END © 2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING