Chemical changes

• Electrolysis 


  The breaking out of a substance using electricity. Used if an element is more reactive than carbon.
• Electrolyte


  The solution which is being broken down during electrolysis. Must be molten (melted) or aqueous to allow ions (charged Particles) to move. Solid will not conduct.
• Aqueous


  Dissolved in water (contains H+ and OH- ions)
• Oxidation


  The loss of electrons or gaining of oxygen
• reduction 


  The gain of electrons or loss of oxygen
• Anode


  The positive electrode
• Cathode


  The negative electrode
• Anion


  Ion that goes to anode ( - negative ion )
• Cation


  Ion that goes to cathode ( + positive ion )
• rules of electrolysis - substance given off

  Negative electrode : least reactive of hydrogen or metal ( hydrogen unless copper, silver or gold present)
• Rules of electrolysis - substance given off

  positive Electrode : group 7 halogen if halide present, oxygen from OH- if not
• Cryolite 


  Lowers melting point of aluminium oxide so reduces energy needed for electrolysis to form aluminium
• Acids


  Contain H+ ions, pH <7 (0-6.9)
• Alkalis 


  Contains OH- ions, pH > 7 (max 14)
• Neutral 


  pH = 7
• Neutralisation


  Reaction between acid and alkali (or base) which produces a salt and water (neutral solution )
• Half equation


  H+ (aq) + OH- (aq) —> H2O (L lower case )
• Indicator 


  changes colour in acids or alkalis e.g. universal indicator , litmus paper
• Crystallisation 


  Separation of salt from solution. Evaporate water partially to concentrate solution. Leave to cool to form crystals.
• Hydrochloric acid —> ____ chloride
• Sulphuric acid —> ____ sulphate
• Nitric acid —> ____ nitrate
• pH of substances 


  0-6.9 = acids

  7.1-14 = alkali

  
• Exothermic reaction 


  Releases energy to the surroundings. Feels hot
• Endothermic reaction 


  Takes in energy from the surroundings. Feels cold
• Chemical reaction 


  Occurs when particles collide with sufficient energy
• Activation energy


  Minimum amount of energy needed for reaction to occur
• Strong/weak acid - HT 


  Strong hydrogen ions fully dissociate e.g. metric, hydrochloric and sulphuric acids / weak hydrogen ions only partially dissociate e.g. ethanoic, citric and carbonic acids
• Concentration - HT


  Amount of solute dissolved in a given volume (dilute/concentrated). Measured in g/dm3 or mol/dm3