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OXIDATION AND REDUCTION

OXIDATION AND REDUCTION. IGCSE Chemistry 620. Gaining of oxygen is called oxidation. Carbon + Oxygen  Carbon dioxide Carbon is oxidised to carbon dioxide. Methane burns in oxygen. CH 4 + 2O 2  CO 2 + 2H 2 O Methane is oxidised to carbon dioxide and water. Rusting of iron

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OXIDATION AND REDUCTION

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  1. OXIDATION AND REDUCTION IGCSE Chemistry 620

  2. Gaining of oxygen is called oxidation. • Carbon + Oxygen  Carbon dioxide • Carbon is oxidised to carbon dioxide. • Methane burns in oxygen. • CH4+ 2O2 CO2+ 2H2O • Methane is oxidised to carbon dioxide and water. • Rusting of iron • 4Fe + 3O2 2Fe2O3 • Iron is oxidised to Iron (III) oxide (rust) • During respiration, glucose is oxidised to CO2and H2O • C6H12O6+ 6O2 6CO2+ 6H2O OXYGEN

  3. Removal of oxygen is called reduction. • When Iron is extracted from haematite, Iron oxide is reduced to Iron. • Fe2O3+ 3CO  2Fe + 3CO2 • CO helps in the reduction of Iron oxide. So CO is called the reducing agent. • When Hydrogen gas is passed over hot copper (II)oxide, Hydrogen reduces copper oxide to copper. Hydrogen is the reducing agent. • CuO + H2 Cu + H2O Oxygen

  4. Oxidation: Loss of electron. • Reduction: Gain of electron. • Na - e  Na+Sodium is oxidised • Cl + e  Cl-Chlorine is reduced • In the above reaction, chlorine helps sodium for oxidation. So chlorine is the oxidising agent. • In the above reaction, Sodium helps chlorine for reduction. So sodium is the reducing agent. • Don’t forget oxidising agent always undergoes reduction and reducing agent always undergoes oxidation Electron transfer

  5. 2Mg + O2 2MgO • 2 Mg + O2  2 [Mg2+][O2-] • In the above reaction which undergoes oxidation and which undergoes reduction? • What is the oxidising agent and what is the reducing agent? • Magnesium looses 2 electrons to form Mg2+ • So magnesium is oxidised. Oxygen is the oxidising agent. • Oxygen gains 2 electrons to formO2-. • So oxygen is reduced. Magnesium is the reducing agent.

  6. Zn + Cu2+ Zn2++ Cu • Zn looses electrons to form Zn2+(oxidation) • Cu2+gains electrons to form Cu (reduction) • Zinc is the reducing agent. • Cu2+is the oxidising agent. • Find the oxidising agent, reducing agent, oxidation and reduction the following reaction: • Cl2(g) + 2Fe2+(aq) → 2Cl-(aq) + 2Fe3+(aq) • Answer: • Chlorine is reduced (electron gained) • Fe2+is oxidised (electron lost) • Chlorine is the oxidising agent (undergoes reduction) • Fe2+is the reducing agent (undergoes oxidation)

  7. Example • 2I-(aq)+ 2Fe3+(aq) → I2(s) + 2Fe2+(aq) • I-undergoes oxidation (reducing agent) • Fe3+undergoes reduction (oxidising agent) • Electroplaing of Silver • Anode: • Ag – e  Ag+(oxidation) • Cathode: • Ag++ e  Ag (reduction)

  8. All atoms and molecules have oxidation number 0 • Ions have oxidation number equals the charge on the ion. • Hydrogen has oxidation number +1 • Oxygen has oxidation number -2 • Halogens have oxidation number -1 • Alkali metals have oxidation number +1 Oxidation number

  9. Chlorine in Cl2 • Carbon in CO2 • Nitrogen in NH3 • Sulphur in H2SO4 • Nitrogen in HNO3 • Iron in FeCl3 • Copper in CuCl2 • Manganese in MnO4- • Chromium in Cr2O72- 0 +4 -3 +6 +5 +3 +2 +7 +6 What is the oxidation number of:

  10. Increase in oxidation number is oxidation • Decrease in oxidation number is reduction • Examples: • Which one undergoes oxidation(reducing agent) • Which one undergoes reduction(oxidising agent) • 1. N2+ 3H2 2NH3 • Nitrogen Oxidation No decreases from 0 to -3 (reduction) • Hydrogen Ox No increases from 0 to +1(oxidation) • 2. Ca+ Cl2 CaCl2 • Oxidation No of Ca increases from 0 to +2 (oxidation) • Oxidation No of Cl decreases from 0 to -1 (reduction)

  11. 3. 2FeCl2+ Cl2 2FeCl3 • Oxidation No of Fe increases from +2 to +3 (oxidation) • Oxidation No of Cl decreases from 0 to -1 (reduction) • 4. 4P + 5 O2 2P2O5 • Oxidation No of P increases from 0 to +5 (oxidation) • ON of O decreases from 0 to -2 (reduction) • 5. HCl+ NaOHNaCl + H2O • Oxidation or reduction does not takes place any. So it is not a redox reaction • A reaction where oxidation and reduction takes place at the same time is called redox reactions. • Neutralisation is not a redox reaction.

  12. 2FeCl2 + Cl2 2FeCl3 • FeCl2 is oxidised (reducing agent) • Cl2 is reduced (oxidising agent) • N2 + 3H2 3NH3 • Nitrogen is reduced (oxidising agent) • Hydrogen is oxidised (reducing agent) • HCl + NaOHNaCl + H2O • No oxidation or reduction • Ca + CuCl2 CaCl2 + Cu • Ca is oxidised (reducing agent) • Cu2+ is reduced (oxidising agent) • Cl2 + 2KBr  2KCl + Br2 • Cl2 is reduced (oxidising agent) • Br- is oxidised (reducing agent)

  13. THE END

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