Chemical Changes

• Reactivity: the tendency of a metal to form positive ions

  Ore: a type of rock that contains metal ions

  Species: a molecule or element within a chemical reaction/equation
• metal + oxygen → metal oxide

  metal + water → metal hydroxide + hydrogen
• • Metals higher than carbon in the reactivity series are extracted using electrolysis – very expensive

  • Metals below carbon are extracted by reduction using carbon e.g. iron oxide is reduced in a blast furnace

  o This is because carbon can displace a metal from its oxide when a metal is less reactive than carbon
• REDuction & OXidation occur at the same time – called REDOX
• • strong acids e.g. hydrochloric, nitric & sulfuric acids

  o completely ionised in aqueous solution

  ▪ all acid particles disassociate to release H+

  ions

  • weak acids e.g. ethanoic, citric & carbonic acids

  o only partially ionised in aqueous solution

  ▪ only a small proportions of acid particles disassociate to release H+

  ions

  o ionisation of a weak acid is a reversible reaction

  ▪ leads to an equilibrium of undissociated and dissociated acid

  ▪ since only a few acid particles release H+

  ions the position of equilibrium lies to the left
• electrolytes - liquids & solutions are able to conduct electricity (must be ionic compounds)

  electrodes - solids that conduct electricity & are submerged in the electrolyte
• o Aluminium oxide is extracted from bauxite ore

  o Aluminium oxide has a very high melting point, so adding cryolite reduces the melting point

  ▪ Cryolite is an aluminium based compound with a lower melting point than aluminium oxide

  • Positive Al3+ ions are attracted to the negative electrode (cathode)

  o they gain 3 electrons to form aluminium atoms which sink to the bottom of the electrolysis tank

  • Negative O2- ions are attracted to the positive electrode (anode)

  o they lose 2 electrons to form oxygen atoms which bond to form O2 molecules which are released
• Aqueous solutions:

  o At the negative electrode (cathode) – H+ ions & positive metal ions are present

  ▪ If the metal is more reactive than hydrogen – hydrogen gas is produced

  ▪ If the metal is less reactive than hydrogen – the pure metal is produced (coats the cathode)

  o At the positive electrode (anode) – OHions & negative non-metal ions are present

  ▪ If halide ions are present – the halogen gas is produced

  ▪ If halide ions aren’t present – oxygen gas is produced (OH ions discharged)