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Umm Al Quwain

Presentation On Redox Reaction (Part 1)

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Published in: Chemistry | Science
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This PPT is suitable for the IGCSE and O Level Chemistry students. It only provides theoretical background of the topic. The worksheets and topical questions will be discussed during the tutoring sessions

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  1. Redox Reactions Chemistry (IGCSE / O-Level)
  2. What will you learn in this lesson? • Defining redox reactions • Identifying redox reactions in terms of gain and loss of oxygen • Identifying redox reactions in terms of gain and loss of electrons • Redox reactions during electrolysis
  3. Combustion, Reduction and Oxidation Combustion: A chemical reaction in which a substance reacts with oxygen and it's an exothermic reaction methane + oxygen —e carbon doxide + water CH4(g) + 202(g) coa(g) + 2H20(g) + oxWu carbon dioxide -+ water CoHi200 + 602 6C02 + In combustion reactions, oxides are formed but not all reactions produce a great amount of energy. For e.g., when air is passed over heated copper, the surface becomes coated with black copper (Il) oxide copper oxygen copper(ll) oxide 2Cu 2CuO
  4. Combustion, Reduction and Oxidation (contd.) Cuo can be converted back to Cu, when hydrogen gas is passed over heated material copper(ll) oxide hydrogen copper + water During this reaction, copper(ll) oxide is losing oxygen. Cuo is going through reduction process. The hydrogen is gaining oxygen; hydrogen is being oxidized. + Cu + H20
  5. Combustion, Reduction and Oxidation (contd.) It is important that you notice the words we use in describing these reactions: if a substance gains oxygen during a reaction, it is oxidised if a substance Loses oxygen during a reaction, It is reduced. Notice that the two processes of oxidation and reductions take place together during the same reaction. A reaction involving both reduction and oxidation is called redox reaction zinc oxide + cart'" zinc + carbon monoxide ZnO + C Zn + CO
  6. Combustion, Reduction and Oxidation (contd.) Reduction helps in extracting metals from metallic oxide ores found in the earth's crust. Extraction of iron(lll) oxide involves two reduction reactions carbon dioxide + carbon carbon monoxide iron(lll) oxide carbon monoxide iron + carbon dioxide Carbon monoxide removes oxygen from iron(lll) oxide. It is an example of reducing agent
  7. Combustion, Reduction and Oxidation (contd.) Reducing Agent: A substance that reduces another substance during a redox reaction and is itself oxidised during the reaction. Hydrogen, carbon and carbon monoxide are common reducing agents Oxidising Agent (or Oxidants): A substance that oxidices another substance during a redox reaction and is itself reduced during the reaction. Oxygen (or air), hydrogen peroxide, potassium permanganate(Vll) and potassium dichromate(Vl) are common reducing agents
  8. Combustion, Reduction and Oxidation (contd.) Reducing agent itself is oxidised (gain oxygen) and reduces (remove oxygen) the other compound Oxidising agent itself is reduced (remove oxygen) and oxidises the other compound Some chemical reactions are listed below, A B C D E 1 2 3 hexane + oxygen carbon cioxide + water magnesium + oxygen —4 mamesium oxide calcium carbonate cüium oxide + carbon dioxide magnesium + copper(ll) oxide magnesium oxide + copper hydrochloric + sodium hydroxide sodium chloride + water Which of these reactions involve oxidation and reduction? Which of these reactions usually involve burning? What type of reaction has happened to the copper(ll) oxide in equation D?
  9. Electron Gain and Loss in Redox Reactions -F amer(ll) oxide +02 2cuo • the copper atoms in the tnetal have become copper ions (Cu2+) in copper(IT) oxide • molecLiles in the gas have split and become oxide ions (02-) in the blatk solid copper(ll) oxide. Copper is clearly oxidised. The atom that gain electrons is reduced. So, in this reaction oxygen is reduced. This method is used to find the redox reaction that does not involve oxygen A nev, broader definition af oxidation and reduction can now be put forward. • oxidation the toss of electrons • reduction is the gain of electrons.
  10. Electron Gain and Loss in Redox Reactions (contd.) OILRIG Oxidation Is the Loss of electrons Reduction Is the Gain of electrons A memory aid for remembering one definition of oxidation and reduction.
  11. Electron Gain and Loss in Redox Reactions (contd.) Displacement reactions: The reactions in which more reactive metal displaces the less reactive metal from its salt solution. Zn(s) + CuS04(aq) ZnS04(aq) + Cu(s) Displacement reactions can now be seen as redox reaction without transfer of oxygen reduction A reaction between zinc and copper Zn(s) + Cu2+(aq) oxidation + Cu(s)
  12. Electron Gain and Loss in Redox Reactions (contd.) Chlorine is a good reducing agent. It displaces iodine from the potassium iodide solution. The ionic equation will be: Cli(aq) + + k(aq) The half equations represent the gain and loss of electrons C12Cg) + 2€ redUction an oxh%tion Chlorine displaces iodine in potassium iodide
  13. Redox during Electrolysis and in Fuel Cells Electrolysis can be seen as a process in which oxidation and reduction are physically separated. In electrolysis of concentrated sodium chloride, hydrogen is formed at cathode (negative electrode) and chlorine is formed at anode (positive electrode) At the cathode : 2H+(aq) + 2e— H2(g) a reduction At the anode : 2 C12(g) + 2e— an oxidation During electrolysis: • the axidatton of non-metal Ions always takes place at the anode • the reduction of metal or hydrogen ions always takes place at the cathode.
  14. Redox during Electrolysis and in Fuel Cells (contd.) Electrolytic decomposition during electrolysis is done by redox at the same time 'OIL RIG' memory aid can be expanded to 'AN OIL RIG CAT' A controlled and highly exothermic oxidation reaction of hydrogen occurs Balloon with hydrogen. b: Hydrogen .xplogively when ignited. in hydrogen-oxygen fuel cells
  15. 4 5 6 Redox during Electrolysis and in Fuel Cells (contd.) Define the following terms, one example of each. a an oxidising agent b a reducing agent Complete the following is the gain af electrons; __is the loss of electrons. During a redox reaction the oxidising agent electrons; the oxidlstng agent is itself during the reaction, Redox means reduction and oxidation. It can be defined by loss and gain of oxygen or by loss and gain of electrons. a Which definiåon is usefuP b Is it possible to have oxidation without reduction in a chemical reaction? Explain your answer.

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