Chemical changes

• Acids and alkalis are on the opposite ends of the pH scale
• Acids and alkalis combine to form water, which is neutral
• Acids


  Substances that form hydrogen (H+) ions when they dissolve in water
• Alkalis


  Substances that form hydroxide (OH-) ions when they dissolve in water
• Alkali


  A type of base
• pH scale


  Used to measure how acidic or alkaline a substance is
• Oxidation


  The gaining of oxygen in a reaction
• Reduction


  The loss of oxygen in a reaction
• OIL RIG


  Oxidation Is Loss, Reduction Is Gain
• Oxidation and reduction reactions are important types of reactions in chemistry
• Oxidation reaction


  Involves gaining oxygen
• Oxidation reactions


  Can also involve losing electrons
• Oxidation reaction example


  • Calcium + oxygen → calcium oxide
  • 2Ca + O2 → 2CaO
• Reduction reaction


  Involves losing oxygen
• Reduction reactions


  Can also involve gaining electrons
• Reduction reaction example


  • Iron oxide + carbon monoxide → iron + carbon dioxide
  • Fe2O3 + 3CO → 2Fe + 3CO2
• Displacement reaction


  A more reactive metal can remove a less reactive metal from a compound
• Displacement order


  A metal can only displace another metal from a compound if it is located above it in the reactivity series
• Displacement reaction example


  • Calcium + copper sulfate → calcium sulfate + copper
  • Ca(s) + CuSO4(aq) → CaSO4(aq) + Cu(s)
• Platinum is less reactive than copper and cannot displace copper from a copper sulfate solution
• Displacement reaction (halogens)


  More reactive substances can displace less reactive substances from compounds
• Displacement reaction example (halogens)

  • Sodium bromide + chlorine → sodium chloride + bromine
  • 2NaBr + Cl2 → 2NaCl + Br2
• Bromide ions (Br-)


  Are oxidised (electrons are lost)
• Bromide ions oxidation example

  • 2Br- → Br2 + 2e-
• Chlorine (Cl2)


  Is reduced (electrons are gained)
• Chlorine reduction example


  • Cl2 + 2e- → 2Cl-
• Spectator ions


  Ions that are unchanged in the reaction
• Sodium ions are spectator ions
• Potassium, sodium and lithium all react quickly with cold water to produce a metal hydroxide and hydrogen gas
• Potassium


  The most reactive metal that reacts very quickly with water
• The hydrogen produced from potassium ignites instantly and the metal sets alight, sparking and burning with a lilac flame
• Sodium


  Fizzes rapidly and melts to form a ball that moves around on the water surface
• Lithium


  Fizzes steadily and floats, becoming smaller until it eventually disappears
• Most metals react with dilute acids to give a salt and hydrogen gas
• Metals that react with dilute acids

  • Magnesium
  • Aluminium
  • Zinc
  • Iron
  • Lead
• Iron and lead react slowly with dilute acids
• Metals that don't react with dilute acids

  • Copper
  • Silver
  • Gold
  • Platinum
• Most metals are only found as compounds because they have reacted with other elements in the past
• Metals that are less reactive than carbon can be extracted from their oxides by reducing with carbon
• Carbon is used because it is cheap and abundant