c4 - chemical changes

• Oxidation

  Is

  Loss of electrons

  Reduction

  Is

  Gain of electrons
• metals can be extracted form their ore by reduction, if the metal is below carbon in the reactivity series
• in electrolysis, magnesium is dissolved in molten cryolite to form a molten magnesium oxide
• weak acids disassociate partially
• strong acids disassociate fully
• disassociation : when acids are put in water, they release H+ ions
• acid + metal = salt + hydrogen
• acid + base = salt + water
• acid + alkali = salt + water
• a reaction between an acid and alkali is neutralisation
• ph value depends on the concentration of H+ ions in a solution and how much it disassociates
• solutions - if the metal is less reactive the hydrogen, then the metal is produced
• metals are extracted at the negative electrode
• non-metals are extracted at the positive elctrode
• electrolysis in molten salts:

  positive ions give an electron to the negative electrode

  negative ions take an electron from the positive electrode
• electrolysis of aqueous solutions :

  if the solution contains a halide, the halogen is formed, else oxygen is formed
• copper leaves behind a brown residue
• hydrogen produced bubbles
• chlorine bleaches blue litmus
• aqueous solutions - if a metal is less reactive than hydrogen, the metal is formed, else hydrogen is formed