Chemical Changes

• Electrolysis


  The process of splitting ionic compounds into elements using an electric current
• Electrolysis


  1. Splitting

  2. Electricity

  3. Break down ionic compounds into elements
• Electrolysis


  • A chemical technique where an electric current is used
  • Ionic compounds must be molten or dissolved in water (solution)
• Why electrolysis is used

  • Extracting metals made from one type of atom
  • Making chlorine gas
  • Making hydrogen gas
  • Making soaps
• Electrolyte


  A liquid or solution that conducts electricity and contains ions that carry electrical charge
• Solids vs molten/solution


  • In solids, ions are in fixed positions so cannot move and cannot carry electrical charge
  • In molten/solution, ions are free to move/mobile and can carry electrical charge
• Oxidation


  The process where a negative ion (anion) loses electrons to turn into an element
• Reduction


  The process where a positive ion (cation) gains electrons to turn into an element
• Electrolysis of molten ionic compounds

  1. Solid ionic compounds are melted

  2. This requires large amounts of energy

  3. The ions are free to move and can carry electrical charge
• Half equations


  Used to show how many electrons an ion loses or gains during oxidation or reduction
• Half equations at the cathode

  • Mg + 2e → Mg
  • Na+ + e → Na
  • Al3+ + 3e → Al
  • 2H+ + 2e → H2
• Half equations at the anode

  • 2Cl- → Cl2 + 2e
  • 2Br- → Br2 + 2e
  • 2I- → I2 + 2e
• Uses of aluminium


  • Food and drink cans
  • Aeroplanes
  • Cooking foil
  • Car bodies
  • Overhead cables
• Properties of aluminium


  • Low density makes it lightweight
  • Strong yet durable
  • Resistant to corrosion
• Extraction of aluminium


  1. Mining the bauxite ore

  2. Extracting aluminium oxide from the bauxite

  3. Making an electrolyte by mixing aluminium oxide with cryolite to lower the melting point
• Electrolysis of molten aluminium oxide

  1. At the negative electrode, Al3+ cations are reduced to form Al atoms

  2. At the positive electrode, O2- anions are oxidised to form O2 gas
• The carbon anode burns away and needs to be replaced regularly as it reacts with the oxygen gas produced
• Reactivity series


  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Aluminium
  • Carbon
  • Zinc
  • Iron
  • Tin
  • Lead
  • Hydrogen
  • Copper
  • Silver
  • Gold
  • Platinum
• What happens in oxidation reactions?

  A substance often gains oxygen
• What occurs in reduction reactions?

  A substance often loses oxygen
• How do oxidation and reduction relate to each other?

  They always occur together
• What do metals form when they react with oxygen?

  Metal oxides
• What is produced when magnesium burns in air?

  Magnesium oxide
• What happens to magnesium in the reaction with oxygen?

  Magnesium gains oxygen and is oxidised
• What can metal oxides undergo to be reduced?

  Removing oxygen
• What happens to lead(IV) oxide when heated with carbon?

  It loses oxygen and is reduced
• What occurs to carbon in the reaction with lead(IV) oxide?

  Carbon gains oxygen and is oxidised
• What happens to metal atoms during reactions?

  They lose electrons to form positive ions
• How is the reactivity of metals determined?

  By how easily they lose electrons
• What do metals produce when they react with acids?

  Metal salts and hydrogen
• Which metals are very reactive with water?

  Lithium, sodium, and potassium
• Why is it unsafe to react lithium, sodium, and potassium with dilute acids?

  They react too vigorously
• Which metals are fairly reactive?

  Calcium, magnesium, zinc, and iron
• Where are very unreactive metals placed in the reactivity series?

  At the bottom
• What does the reactivity series include for comparison?

  Carbon and hydrogen
• What is a displacement reaction?

  • A more reactive metal displaces a less reactive metal
  • Example: Magnesium displaces copper from copper sulfate
• What determines the method of extraction for metals?

  How reactive the metal is
• How do unreactive metals exist at the Earth's surface?

  As elements
• How are metals less reactive than carbon extracted?

  By heating with carbon
• What happens to iron oxide when heated with carbon?

  It loses oxygen and is reduced