Chemical Changes

• Acid


  Produces hydrogen ions (H+) in aqueous solutions, pH range 0-6
• Alkali


  Produces hydroxide ions (OH-) in aqueous solutions, pH range 8-14
• Crystallisation


  A separation technique used to produce solid crystals from a solution by evaporating the solvent
• Displacement


  A chemical reaction in which a more reactive element displaces a less reactive element from its compound
• Electrolysis


  The splitting up of an ionic compound using electricity, causing chemical reactions at the electrodes and the decomposition of the materials
• Electrolyte


  A solution containing free ions from the molten or dissolved ionic substance, where the ions are free to move to carry charge
• Extraction


  Techniques used to separate a desired substance when it is mixed with others
• Filtration


  A separation technique used to separate solids from liquids
• Negative electrode (cathode)


  The electrode where hydrogen is produced if the metal in the electrolyte is more reactive than hydrogen, where positively charged ions gain electrons and so the reactions are reductions
• Neutralisation


  The reaction when an acid and a base react to form water and a salt
• Oxidation


  A reaction involving the gain of oxygen, oxidation is the loss of electrons
• pH scale


  The scale from 0 to 14 that measures the acidity or alkalinity of a solution, can be measured using universal indicator or a pH probe
• Positive electrode (anode)


  The electrode where oxygen is produced unless the solution contains halide ions then the halogen is produced, where negatively charged ions lose electrons and so the reactions are oxidations
• Reduction


  A reaction involving the loss of oxygen, reduction is the gain of electrons
• Reduction with carbon


  Metals less reactive than carbon can be extracted from their oxides by reduction with carbon
• Strong acid


  A strong acid is completely ionised in aqueous solution, examples are hydrochloric, nitric and sulfuric acids
• Reactivity series


  Metals are arranged in order of their reactivity, can be used to predict products from reactions
• Universal indicator


  A mixture of dyes that changes colour gradually over a range of pH and is used in testing for acids and alkalis
• Weak acid


  A weak acid is only partially ionised in aqueous solution, examples are ethanoic, citric and carbonic acids