C4 Chemical Changes

• Universal Indicator

  a wide range indicator that changes colour depending on the pH.

  It gives an approximate pH value.
• pH Scale


  0 - 14
• pH Range


  • 0-6 Acids
  • 7 Neutral
  • 8-14 Alkalis
• Acids


  Form H+ ions in water
• Alkalis


  Form OH- ions in water
• Two Ways to Measure pH

  1. Universal Indicator

  2. pH Probe
• Universal Indicator


  Wide range indicator that changes colour depending on the pH, gives approximate pH value
• pH Probe


  Gives an accurate pH value
• Neutralisation Reactions


  1. Acid + Metal/Alkali -> Salt + Water

  2. Acid + Metal Carbonate -> Salt + Water + Carbon Dioxide
• The products of neutralisation reactions are neutral
• To get the formula of a salt, balance the charges of the ions so the overall charge is neutral
• Reactions of Acids


  • Acid + Metal Carbonate -> Salt + Water + Carbon Dioxide
  • Acid + Metal Oxide -> Salt + Water
  • Acid + Metal Hydroxide -> Salt + Water
• Double Salts


  Made by adding metals/soluble metal compounds to acids, the insoluble salt is filtered off and the remaining salt solution is crystallised
• Acids Used to Produce Salts


  • HCl -> Chloride
  • H2SO4 -> Sulfate
  • HNO3 -> Nitrate
• Reactivity Series


  Metals arranged in order of decreasing reactivity
• Reactivity Series

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Aluminium
  • Carbon
  • Zinc
  • Iron
  • Copper
  • Hydrogen
• Extraction of Metals


  1. Metals more reactive than carbon extracted from molten compounds by reduction using carbon

  2. Metals less reactive than carbon extracted from molten compounds by electrolysis
• Some unreactive metals like gold are found in the earth as the metal itself
• Oxidation


  Gain of oxygen
• Reduction


  Loss of oxygen
• Reactivity of metal


  Faster bubbles of hydrogen produced with more reactive metals in acid
• Electrolysis of Molten Ionic Compounds


  Positive metal ions move to cathode, negative ions move to anode, molten metal sinks to bottom
• Electrolysis of Aqueous Ionic Compounds


  Negative ions move to anode, metal produced at cathode if less reactive than hydrogen, oxygen and hydrogen produced at anode if no halide ions present, halogen produced at anode if halide ions present
• Electrolysis of molten aluminium oxide mixed with cryolite produces aluminium metal