Chemistry

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  • Created by: AOconnor
  • Created on: 14-05-18 19:42
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  • Chemistry
    • Electrolysis
      • Decomposition of aqueous/molten ionic compounds using electricity
        • Molten compounds (lead bromide)
          • Process
            • Melt lead bromide
              • Positively charged lead ions go to cathode and form pure lead
              • Negatively charged bromide ions go to anode and form bromine
          • Half equations
            • Anode
              • 2Br(-)  ---> Br2 + 2e(-)
            • Cathode
              • Pb(2+) + 2e(-) ---> Pb
        • Aqueous solutions
          • Aqueous means dissolved in water
          • Water molecules break down to form OH- and H+
          • Anode
            • If halide ions are present, the halogen is produced
              • Halide ions = fluoride, chloride, bromide and iodide
            • If no halide ions present, oxygen is produced
              • Halide ions = fluoride, chloride, bromide and iodide
          • Cathode
            • Least reactive element is formed out of hydrogen and metal
        • Extracting metals (aluminium from aluminium oxide)
          • Extracts metals more reactive than carbon
            • Requires lots of energy and can be expensive
            • Aluminium can be obtained via electrolysis of aluminium oxide
              • Mixed with cryolite which lowers melting point so less energy needed (cheaper)
              • Aluminium formed at cathode
                • Al(3+) + 3e(-) ---> Al
              • Oxygen gas forms at anode
                • Anode is carbon, so reaction occurs and carbon dioxide is formed
                • 2O(2-) ---> O2 + 4e-
      • Ionic compound must be in liquid form so ions can move freely and carry charge
      • Electrodes are made from solids that can conduct electricity but are inert
      • Substance being broken down is the electrolyte
      • Anode is positive and cathode is negative
    • Reactivity of metals
      • Oxidation is gaining oxygen
      • Reduction is losing oxygen
        • Metal oxides can be reduced by removing oxygen
          • Lead oxide is reduced by heating with carbon to form lead and carbon dioxide
      • Metals react with acids to produce salts and hydrogen
        • Doing thee reaction can help place elements on reactivity series
      • Method used to extract metals depends on its reactivity
        • Most metals are found as metal oxides in earths crust
        • Metals less reactive than carbon can be extracted by heating with carbon
    • Alkalis
      • Hydroxide ions make solutions alkaline
      • 8-14
      • Strong alkalis fully disassociate in water
        • All OH- ions are released
      • Alkalis are soluble bases
    • Acids
      • hydrogen ions make solutions acidic
      • 1-6
      • Strong acids fully ionise in water
        • All hydrogen ions are released
        • Strong acids have a higher concentration of H+ ions
      • Neutralisation
        • Acids are neutralised by soluble bases
          • When they react the OH- ions and H+ ions react to form water
            • Solution reaming is neutral (pH = 7)
            • A salt is produced when the hydrogen ion in the metal is replaced by a metal ion
        • Acid + metal hydroxide ---> salt +water
        • Acid + Metal oxide ---> salt + water
        • Acid + metal carbonate ---> salt + water + carbon dioxide
    • Salts
      • Soluble salts are made by reacting acids with insoluble bases
        • Practical
          • Add metal oxide/carbonate to warm solution of acid until no more will react
            • Filter excess metal oxide/carbonate to leave solution of salt
              • Warm solution so water evaporates and crystals form

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