Chapter 1 (redox)

• Redox reactions

  Chemical reactions involving oxidation and reduction occurring simultaneously
• Aspects to understand Redox reactions

  • Losing or gaining oxygen
  • Losing or gaining hydrogen
  • Changing of oxidation number
  • Transferring of electron
• Redox in terms of Oxygen transfer

  1. Oxidation is gain of oxygen

  2. Reduction is loss of oxygen
• Redox in terms of Oxygen transfer


  • In the extraction of iron from its ore: Fe2O3 + 3CO → 2Fe + 3CO2
• Substance gaining oxygen


  • Said to be oxidised (undergoes oxidation)
• Substance losing oxygen

  • Said to be reduced (undergoes reduction)
• Oxidising Agents and Reducing agent

  1. The substance that causes oxidation is called oxidising agent

  2. The substance that causes reduction is called reducing agent

  3. Oxidising agents give oxygen to another substance

  4. Reducing agents remove oxygen from another substance
• Redox in terms of Hydrogen transfer

  1. Oxidation is loss of hydrogen

  2. Reduction is gain of hydrogen
• Redox in terms of Hydrogen transfer

  • Ammonia can be oxidised to form nitrogen gas: 2NH3(g) + 3Br2 → N2(g) + 6HBr(g)
• Substance losing hydrogen

  • Said to be oxidised (undergoes oxidation)
• Substance gaining hydrogen

  • Said to be reduced (undergoes reduction)
• Oxidising Agents and Reduction agent

  1. The substance that causes oxidation is called oxidising agent

  2. The substance that causes reduction is called reducing agent

  3. Oxidising agents give oxygen to another substance or remove hydrogen from it
• Oxidising agent


  Substance that causes oxidation (oxidises something else)
• Reducing agent

  Substance that causes reduction (reduces something else)
• Oxidising agents give oxygen to another substance or remove hydrogen from it
• Reducing agents remove oxygen from another substance or give hydrogen to it
• Oxidising agent

  • potassium permanganate (KMnO4), Hydrogen peroxide (H2O2), chlorine water (Cl2), concentrated nitric acid
• Reducing agent

  • active metals such as sodium, magnesium, sulphur dioxide (SO2), hydrogen sulphide (H2S)
• REDOX in terms of Electron transfer

  1. Oxidation occurs when a reactant loses electron

  2. Reduction occurs when a reactant gains electron
• In the reaction, Magnesium metal loses 2 electrons to form magnesium ions
• In the reaction, Copper gains 2 electrons to form copper metal
• Gain of oxygen
• Gain of hydrogen
• Loss of hydrogen
• Ionic equation

  1. Joins the 2 half equations

  2. Cancel both side electrons
• Oxidising agent: CuO
• Reducing agent: Mg
• Oxidation occurs when a reactant loses an electron
• Reduction occurs when a reactant gains an electron
• In this reaction, sodium atom loses 1 electron to form a sodium ion
• In this reaction, each molecule of chlorine accepts 2 electrons to form 2 chloride ions
• Marginal utility

  The additional utility (satisfaction) gained from the consumption of an additional product
• If you add up marginal utility for each unit, you get total utility
• 1. 2Fe2+ → 2Fe3+ + 2e- is an oxidation reaction
• 1. Mg → Mg2+ + 2e- is an oxidation reaction
• 1. Cl2 + 2e- → 2Cl- is a reduction reaction
• 1. O2 + 4e- → 2O2- is a reduction reaction
• Oxidation state shows the total number of electrons which have been removed from an element (positive oxidation state) or added to an element (negative oxidation state) to get to its present state
• All elemental state has an oxidation number of 0
• Potassium in elemental state has an oxidation number of 0, but when it loses an electron, it becomes K+ with an oxidation state of +1