C4: Chemical changes

• Metals by reactivity


  • Most reactive
  • Less reactive
• Metals


  • Things above carbon in reactivity series need electrolysis to be extracted
  • Things below carbon can be extracted by reduction
• Unreactive metals


  • Generally found in earth as pure, unreacted ores
  • Everything else is generally found as metal oxides
• Metal more reactive than hydrogen


  Hydrogen gas produced in electrolysis
• Metal less reactive than hydrogen


  Something else produced in electrolysis
• Magnesium chloride + calcium

  Calcium chloride + magnesium
• Magnesium chloride + aluminium


  No reaction
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Anode


  Positive electrode
• Cathode


  Negative electrode
• Balancing half-equations


  1. Balance elements

  2. Make charge neutral by adding electrons
• Reactions of acids with metals

  • Acid + metal = salt + hydrogen
  • Acid + metal oxide = salt + water
  • Acid + metal hydroxide = salt + water
  • Acid + metal carbonate = salt + water + carbon dioxide
• Making copper sulfate


  1. Heat sulfuric acid

  2. Stir in copper oxide until in excess

  3. Filter to remove excess copper oxide

  4. Evaporate to leave copper sulfate crystals
• pH scale


  1 = acidic, 7 = neutral, 14 = alkaline
• Acidity


  Caused by hydrogen ions
• Alkalinity


  Caused by hydroxide ions
• Acid-base titration


  1. Pipette alkali into flask

  2. Add acid from burette until colour change

  3. Repeat to get accurate volume
• Titration indicators


  • Phenolphthalein - pink in alkali, colourless in acid
  • Methyl orange - yellow in alkali, red in acid
• Titration calculations


  1. Calculate moles of acid used

  2. Use moles of acid to find moles of alkali

  3. Use moles and volume to calculate alkali concentration
• Strong acids


  Fully dissociate into ions (e.g. HCl, HNO3, H2SO4)
• Weak acids


  Only partially dissociate into ions
• Conductivity


  Requires molten or dissolved state for ions to move freely
• Aluminium electrolysis


  1. Positive anode - oxygen gas evolved

  2. Negative cathode - molten aluminium collected
• Common electrolysis setups


  • Sodium chloride - H2, Cl2, NaOH
  • Sodium sulfate - H2, O2
  • Copper chloride - Cu, Cl2
  • Copper sulfate - Cu, O2
• Electrolysis


  • Positive electrode - oxidation
  • Negative electrode - reduction
  • Test for gases - hydrogen (squeaky pop), oxygen (relights glowing splint), chlorine (bleaches litmus)