Redox

• Redox reaction


  A reaction in which both oxidation and reduction takes place simultaneously in the same reaction
• Oxidation


  Gains oxygen, loses hydrogen, loses electrons, increases in its oxidation state
• Reduction


  Loses oxygen, gains hydrogen, gains electrons, decreases in its oxidation state
• Identifying oxidation and reduction in a reaction

  1. Ensure the chemical equation for the reaction is balanced

  2. The substance that has been oxidised/reduced is the reactant in the reaction

  3. Compare the gain/loss of oxygen/hydrogen on both sides of the reaction to check which reactant has been oxidised/reduced
• Oxidation and reduction examples

  • Heating copper(II) oxide in the presence of hydrogen gas
  • Heating zinc oxide in the presence of carbon monoxide
  • Heating ammonia with oxygen
  • Hydrogen sulfide gas and chlorine gas are mixed to form sulfur and hydrogen chloride
  • Magnesium reacts with chlorine to form magnesium chloride
  • Copper reacts in silver nitrate solution to form copper(II) nitrate and silver
• Oxidation state


  The charge of an atom of an element would have if it existed as an ion in a compound (even if it is covalently bonded)
• Calculating oxidation state of atoms in a reaction

  Write the balanced chemical equation

  2. Determine the oxidation state of all atoms/ions in the reaction
• Oxidation state

  The state of oxidation of an element in a compound, indicated by a number
• Oxidising agent


  A substance that causes another substance to be oxidised, while itself is being reduced
• Reducing agent


  A substance that causes another substance to be reduced, while itself is being oxidised
• Common oxidising agents

  • Oxygen (O2)
  • Acidified Potassium manganate (VII) (KMnO4)
  • Hydrogen peroxide (H2O2)
  • Potassium dichromate (VI)
• Common reducing agents

  • Carbon (C)
  • Carbon monoxide (CO)
  • Potassium iodide (KI)
  • Sulfur dioxide(SO2)
• Identifying oxidising and reducing agents in a reaction

  1. Reaction 1: Cl2(g) + H2S (g) → 2HCl(g) + S(s)

  2. Oxidising agent: Chlorine

  3. Reducing agent: Hydrogen sulfide

  4. Reaction 2: Zn(s) + CuSO4 (aq) → ZnSO4 (aq)+ Cu (s)

  5. Oxidising agent: Copper(II) sulfate

  6. Reducing agent: Zinc
• Testing for an oxidising agent


  1. Use potassium iodide (KI) solution

  2. Observation: Colourless solution turns brown

  3. Explanation: Iodide ions (I-) oxidised to iodine (I2)
• Testing for a reducing agent


  1. Use acidified potassium manganate (VII) (KMnO4) solution

  2. Observation: Purple solution becomes colourless

  3. Explanation: MnO4- (oxidation state +7) reduced to Mn2+
• Reduction involves gaining electrons, while oxidation involves losing electrons.