Chem Topic 4

• What is the reactivity series?

  potassium

  sodium

  calcium

  magnesium

  aluminium

  carbon

  zinc

  iron

  tin

  lead

  hydrogen

  copper

  silver

  gold

  platinum
• What happens as you go up the reactivity series?

  Elements become more reactive
• What is a displacement reaction?

  When a more reactive metal displaces a less reactive metal from a compound.
• What happens when group 1 metals react with hydrogen?

  Group 1 metals are more reactive, so they displace it to produce hydrogen gas and a metal hydroxide
• How can we use displacement reactions to obtain metals from ores?

  We displace the metal from their ore with a more reactive, less valuable metal or carbon. This happens in a blast furnace: iron oxide is reduced to produce iron
• What is oxidisation?

  Loss of electrons
• What is reduction?

  Gain of electrons
• What happens when an acid reacts with an alkali?


  When an acid (pH<7) reacts with an alkali (pH>7), a salt and water (pH=7, neutral) are produced (if reacted completely)
• What is the word equation for this?

  Acid + Alkali -> Salt + Water
• What different types of acid form what types of salt?

  Sulphuric acid: metal sulphate salt

  Nitric acid: metal nitrate salt

  Hydrochloric acid: metal chloride salt
• What happens when salt is left in a solution?

  It means we have a mixture of dissociated ions, Na+, Cl-, H+ and OH-
• How can we obtain crystals of dissolved salts?

  By heating gently it means the water evaporates leaving only the salt behind
• Why do acids have a pH of <7 & why do alkali's have a pH of >7?


  Acids have pH of <7 due to H+ ions, whereas alkali has pH>7 due to OH- ions
• What pH is water?


  Neutral pH of 7 as it always has an equal number of both
• What happens when a change of 1pH occurs?


  A 10x change in concentration of H+ ions or OH- ions
• What do universal indicators do & what are some examples of it?

  Gives you an indication of pH by changing colour

  E.g. Methyl orange, Phenolphthalein
• What do strong acids do?


  Completely ionises when in solution (e.g. hydrochloric, sulphuric, nitric)
• What do weak acids do?


  Partially ionises (ethanoic, carbon, citric)
• What is electrolysis?


  Passing an electrical current through a substance to cause oxidisation and reduction at two electrodes: Anode (+) & Cathode (-)
• When can we only use electrolysis?

  When ions are free to move, so for ionic compounds this can only happen when molten or in solution
• What happens in electrolysis of molten compounds?

  A molten version of the ionic compound is poured into a beaker containing the anode and cathode connected to a cell, this provides the electrical current. The anion is attracted to the anode and the cation is attracted to the cathode.
• Why is cryolite used in the electrolysis of aluminium oxide?

  Lowers the melting point making the electrolysis process cheaper
• Why are the electrodes made from graphite?

  Graphite is conductive and inert meaning they do not react with the electrolyte
• What happens during the electrolysis of a solution?

  For a solution such as sodium hydroxide, the halide ion (Cl-) is oxidised at the anode and the H+ ion is reduced at the cathode.
• Why can solution be able to conduct electricity?

  For a solution that contains an element such as sodium, it can conduct electricity due to the dissolved ions being able to move freely in the mixture and carry on an electric current