CHEMICAL CHANGES

• Oxidation


  When a substance gains oxygen
• Reduction


  When a substance loses oxygen
• Reactivity series of metals

  • Shows the metals in order of their reactivity
  • Metals above H2 in reactivity series react with acid to produce H2. The more reactive the metal is, the quicker and more violent reaction with acid occurs.
  • Metals below H2 don't react with acids.
  • Not all metals above H2 react with water - mostly Group I and II metals. Aluminium is the borderline case.
• Displacement reaction


  A reaction where a more reactive metal displaces a less reactive metal from a compound
• Unreactive metals are found in their natural state in Earth
• Extracting metals less reactive than carbon


  Reduction with carbon. Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure metal.
• Extracting metals more reactive than carbon

  By electrolysis
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Reaction between metals and acids


  Metal + acid → salt + hydrogen
• Type of reaction between metals and acids


  Redox reaction, also a displacement reaction
• Metals above hydrogen in the reactivity series will react with acid
• Neutralisation reaction


  Base + acid → salt + water
• Reaction between metal carbonate and acid


  Metal carbonate + acid → salt + water + carbon dioxide
• Reaction between metal oxides and acids


  Metal oxide + acid → a salt + water
• Redox reaction


  A reaction where both oxidation and reduction occurs
• When magnesium reacts with hydrochloric acid, magnesium has been oxidised (Mg to Mg2+) and the hydrogen in HCl has been reduced (H+ to H2)
• Forming a soluble salt


  React the excess acid with some insoluble chemical (e.g. metal oxide)

  1. Filter off the leftovers
  2. Crystallise the product
• Acids produce hydrogen ions, alkalis produce hydroxide ions in aqueous solutions
• Bases, acids and alkalis


  Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions
• pH scale


  The measure of acidity/alkalinity of a solution; neutral solution has a pH of 7
• Neutralisation reaction (ionic form)

  H+ + OH− → H2O
• Strong acid


  Completely ionised in aqueous solution
• Weak acid


  Only partially ionised in aqueous solution
• As concentration of H+ increases


  pH decreases
• pH of 7


  Measure of acidity/alkalinity of a solution; neutral solution
• Neutralisation reaction


  H+ + OH− → H2O
• Concentrated acid


  Has more moles of acid per unit volume than dilute
• Dilute acid


  Solutions of low concentrations
• Concentration is not the same as strength of an acid
• As pH is decreased by one unit


  Hydrogen ion concentration increases by a factor of 10
• Electrolysis


  The passing of an electric current through ionic substances that are molten or in solution to break them down into elements; ions are discharged (they lose/gain electrons) at electrodes to produce these
• Electrolyte


  The liquid/solution which conducts electricity
• Cathode


  Negative electrode
• Anode


  Positive electrode
• Electrolysis


  1. Reduction occurs at the cathode

  2. Oxidation occurs at the anode
• In aqueous electrolysis, the less reactive element discharges at the cathode. Hydrogen is produced unless there is a less reactive metal, in which case the said metal is produced. Oxygen is produced at the anode unless the solution contains halide ions, in which case halogen molecules are produced.
• Aluminium manufacturing


  1. Electrolysis of aluminium oxide and cryolite

  2. Lots of energy needed which makes it expensive
• Aluminium extraction


  1. Al3+ + 3 e− → Al (cathode)

  2. 2 O2− → O2 + 4 e− (anode)

  3. Oxygen reacts with C of the anode producing CO2
• Cryolite

  Lowers the melting point of aluminium oxide, reducing energy costs