chemical changes (C5 and C6)

• equation for metal and oxygen:

  Metal + oxygen → metal oxide
• equation for metals and acid:

  Metal + acid → metal salt + hydrogen
• equation for metal oxides/hydroxides and acid:

  Metal oxide + acid → metal salt + water
• equation for metal carbonates and acid:

  Metal carbonate + acid → metal salt + carbon dioxide + water
• the ph scale is a measure of the acidity or alkalinity of a solution
• if the ph is 7 the solution is neutral
• if the ph is less than 7 it is acidic
• if the ph is more than 7 the solution is alkaline
• As the H+ ion concentration of the solution increases by a factor of 10, the pH value decreases by 1 unit.
• strong acids ionise completely in a solution
• weak acids only weakly ionise in a solution
• Making a soluble salt:

  1. keep adding the metal compound until small amount remains unreacted in the beaker
  2. filter the mixture to remove any unreacted solid
  3. the soluble salt is present in the solution. Gently heat the solution to evaporate the water
  4. stop heating the mixture when crystals start to appear. Allow the water to evaporate slowly and the soluble salt will start to crystallise. Leave the crystals to dry.
• displacement is when a more reactive metal takes the place of a less reactive metal in a compound
• reduction is when oxygen is lost from a compound
• oxidation is when oxygen is gained by an element or molecule
• oxidation is the loss of electrons
• reduction is the gain of electrons
• electrolysis is the breakdown of a substance containing ions by electricity
• electrolyte is a liquid that conducts electricity when it is in contact with an electrode
• at the cathode positive ions are attracted to the negative electrode and gain electrons to produce elements
• at the anode negative ions are attracted to the positive electrode and lose electrons to produce elements
• aluminium oxide is dissolved in molten cryolite and this reduces the energy cost for the reaction as cryolite has a lower melting point than aluminium oxide
• oxygen is produces at the positive electrode during electrolysis of aluminium oxide
• the positive electrode needs replacing regularly during the electrolysis of aluminium oxide because the electrode is made from carbon which reacts with oxygen being formed at the electrode to create carbon dioxide. The carbon dioxide escapes as a gas and the electrode gradually decreases in size 
• during the electrolysis of the aluminium oxide aluminium is produced
• during the electrolysis of an aqueous solution at the negative electrode if the metal is more reactive than hydrogen then hydrogen is produced, if it is less reactive than hydrogen then the metal is produced
• during electrolysis of an aqueous solution at the positive electrode Oxygen and water are produced unless the solution contains halide ions in which case the halogen would be produced
• gold and some other unreactive metals can be found in their native state
• the reaction between a metal and an acid produces hydrogen gas as well as a salt
• the reaction between a metal and an acid is an example of a redox reaction, the metal atoms lose electrons and are oxidised
• when an acid reacts with a base, a neutralisation reaction occurs
• a pure, dry sample of the salt made in an acid-base reaction can be crystallised out of solution by evaporating off most of the water and drying with filter paper
• Metals can ordered by their reactivity by comparing their reactions with water, acid or oxygen
• Some metals are more reactive than other because they lose their outer shell electrons more easily
• A spectator ion is an ion that is unchanged in a reaction
• Salt is a compounds formed when a metal ion takes the place of a hydrogen ion in an acid
• In the process of electrolysis, an electric currentis passed through an electrolyte.
• An electrolyte is a liquid or solution that contains ions and so can conduct electricity. This causes the ions to move to the electrodes, where they form pure elements
• cathode (negative electrode)
• anode (positive electrode)