C5: Chemical Changes


C5.1: The Reactivity Series

  • the metals can be placed in order of reactivity by their reactions with water and dilute acid
    • potassium
    • sodium
    • lithium
    • calcium
    • magnesium
    • aluminium
    • zinc
    • iron
    • tin
    • lead
    • copper
    • silver
    • gold
  • hydrogen gas is given off if metals react with water or dilute acids.
  • the gas pops with a lit splint
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C5.2: Displacement Reactions

  • a more reactive metal will displace a less reactive metal from its aqueous solution
  • the non-metals hydrogen and carbon can be given positions in the reactivity series on the basis of displacement reactions
  • oxidation is the loss of electrons
  • reduction is the gain of electrons
  • Oxidation Is Loss, Reduction Is Gain
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C5.3: Extracting Metals

  • a metal ore contains enough of the metal to make it economic to extract. ores are mined and may need to be concentrated before the metal is extracted and purified
  • gold and other unreactive metals can be found in their native state
  • the reactivity series helps decide the best way to extract a metal from its ore
  • the oxides of metals below carbon can be reduced by carbon to give the metal element
  • metals more reactive than carbon must be extracted by electrolysis
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C5.4: Salts from Metals

  • a salt is a compoud formed when the hydrogen in an acid is wholly or partially replaced by metal or ammonium ions
  • salts can be made by reacting a suitable metal with an acid
  • the metal must be above hydrogen in the reactivity series, but not dangerously reactive
  • the reaction between a metal and an acid produces hydrogen gas and a salt
  • a sample of the salt made can be crystallised by evaporating the water
  • the reaction between a metal and an acid is a redox reaction
  • the metal atoms lose electrons (oxidation) and the hydrogen ions gain electrons (reduction)
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C5.5: Salts from Insoluble Bases

  • when an acid reacts with a base, a neutralisation occurs
  • the reaction between an acid and a base produces a salt and water
  • the sum of the charges on the ions equal 0
  • this enables you to work out the formula of salts (knowing the charges present)
  • a pure, dry sample of the salt made in an acid-base reation can be crystallised out of solution by evaporating off most of the water and drying with filter paper when needed.
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C5.6: Making More Salts

  • an indicator is needed when a soluble salt is prepared by reacting an alkali and an acid
  • the experiment can be repeated without the indicator to make a salt, then a pure, dry sample of its crystals
  • a carbonate reacts with an acid to produce a salt, water and carbon dioxide gas
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C5.7: Neutralisation and the pH Scale

  • acids are substances that produce H+(aq) ions when they are added to water
  • bases are substances which will neutralise acids
  • an alkali is a soluble hydroxide and alkalis produce OH-(aq) ions when added to water
  • the pH scale shows how acidic or alkaline a solution is
  • solutions with a pH less than 7 are acids, above 7 are alkaline and a pH of 7 is neutral
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C5.8: Strong and Weak Acids

  • aqueous solutions of weak acids such as carboxylic acids have a higher pH value than solutions of strong acids with the same concentration
  • as the pH decreases by 1 unit, the hydrogen ion concentration increases by a factor of 10
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