C4 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 in aqueous solutions
• Alkalis


  Produce hydroxide ions in aqueous solutions
• Bases


  Compounds that neutralise acids
• Alkalis


  Soluble bases - produce hydroxide ions in aqueous solutions
• pH scale


  Measure of acidity/alkalinity of a solution; neutral solution has pH 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


  Solution of low concentration
• 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


  Passing of an electric current through ionic substances that are molten or in solution to break them down into elements
• Electrolyte


  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