Topic 4 - Chemical Changes

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  • Created on: 03-11-18 19:21
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  • Topic 4 - Chemical Changes
    • Acids & Bases
      • pH Scale = measure of how acidic or alkaline a solution is
      • Acid = substance that forms aqueous solutions with pH of less than 7 - form H+ ions
      • Base = substance with pH greater than 7
      • Alkali = base that dissolves in water to form solution with pH greater than 7 - form OH- ions in water
      • Neutralisation - acid + base GIVES salt + water
    • Strong Acids & Weak Acids
      • Strong Acid = ionise completely in water & all acid particles dissociate to release H+ ions
      • Weak Acid = don't fully ionise in solution & only small proportion of acid particles dissociate to release H+ ions
      • Ionisation of weak acid = reversible reaction = sets up equilibrium (position of this = left) between undissociated & dissociated acid
      • If concentration of H+ ions is higher, rate of reaction = faster so strong acids = more reactive than weak acids of same concentration
      • pH = measure of concentration of H+ ions in solution
      • Acid strength = tells what proportion of acid molecules ionise in water  WHERE AS Concentration = measures how much acid is in certain volume of water
    • Reactions of Acids
      • Metal Oxides & Metal Hydroxides = Bases
        • Acid + Metal Oxide GIVES Salt + Water
        • Acid + Metal Hydroxide GIVES Salt + Water
      • Acid + Metal Carbonate GIVES Salt + Water + Carbon Dioxide
    • Reactivity Series
      • How well a metal reacts
      • The higher up the reactivity series a metal is, the more easily they form positive ions (by losing electrons)
        • Higher a metal is in the reactivity series, the more easily it reacts with water or acid
      • acid + metal GIVES salt + hydrogen
      • metal + water GIVES metal hydroxide + hydrogen
      • More reactive the metal, the faster the reaction will go
      • Investigate reactivity of metals by measure temp change of reaction with acid or water over set time period
        • If use same mass & surface area of metal each time - more reactive the metal, the greater temp change should be
    • Separating Metals from Metal Oxides
      • Metals often have to be separated from their oxides
      • Reduction Reaction
      • Formation of Metal Ore: Oxidation = Gain of Oxygen
      • Extraction of Metal: Reduction = Loss of Oxygen
      • Some metals = Extracted by Reduction with Carbon
      • Metals HIGHER THAN CARBON in Reactivity Series = extracted using electrolysis
        • Metals BELOW CARBON = extracted by Reduction using Carbon
    • Redox Reactions
      • If electrons = transferred
      • OILRIG
      • Displacement Reactions are Redox Reactions
        • Rule - A more reactive metal will DISPLACE a less reactive metal from its COMPOUND
        • Metal ion = gains electrons and is reduced - metal atom = loses electrons and is oxidised


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