Chemical Changes

• Reactivity series


  Metals vary in their reactivity as some donate their electrons more readily than others
• Reactivity series


  • Hydrogen
  • Carbon
  • Most common metals
• More reactive metal


  Displaces a less reactive metal from a compound
• Alkali metals


  React with water, displacing hydrogen
• Extracting metals from ores

  1. Any metal less reactive than carbon can be displaced by it

  2. This is called smelting

  3. The oxide has been reduced, oxygen is lost
• Oxidation and reduction


  Oxidation is loss of electrons, reduction is gain of electrons
• Metals more reactive than hydrogen


  Can displace it from an acid
• Acids and alkalis


  • Acids have pH less than 7, alkalis have pH greater than 7
  • They react to produce a salt and water, neutralizing each other
• Dissolving substances


  • Ions partially dissociate, including water into H+ and O- ions
  • Solid crystals can be obtained by evaporating the water
• pH scale


  • Logarithmic scale base 10, not linear
  • Lower pH means higher concentration of H+ ions
• Strong and weak acids

  Strong acids dissociate completely, weak acids only partially dissociate
• Titration


  1. Measure volume of alkali

  2. Add acid of unknown concentration slowly until neutralization occurs

  3. Calculate acid concentration from volumes and moles
• Electrolysis


  • Melting ionic compounds allows ions to move and conduct electricity
  • Positive metal ions (cations) move to negative electrode (cathode) and are reduced
  • Negative ions (anions) move to positive electrode (anode) and are oxidized
• Electrolysis examples


  • Aluminium oxide
  • Sodium chloride solution
• Aluminium oxide is mixed with cryolite to reduce its melting point, making it cheaper to extract aluminium
• Metals by reactivity


  • Most reactive
  • Less reactive
• Metals


  • Things above carbon in reactivity series need electrolysis to be extracted
  • Things below carbon can be extracted by reduction
• Unreactive metals


  • Generally found in earth as pure, unreacted ores
  • Everything else generally found as metal oxides
• Metal more reactive than hydrogen


  Hydrogen gas produced in electrolysis
• Metal less reactive than hydrogen


  Something else produced in electrolysis
• Magnesium chloride + Calcium

  Calcium chloride + Magnesium
• Magnesium chloride + Aluminium


  No reaction
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Anode


  Positive electrode
• Cathode


  Negative electrode
• Balancing half-equations


  1. Balance elements

  2. Make charge neutral by adding electrons
• Reactions of acids with metals

  • Acid + Metal = Salt + Hydrogen
  • Acid + Metal Oxide = Salt + Water
  • Acid + Metal Hydroxide = Salt + Water
  • Acid + Metal Carbonate = Salt + Water + Carbon Dioxide
• Making copper sulfate


  1. Heat sulfuric acid

  2. Stir in copper oxide until in excess

  3. Filter to remove excess copper oxide

  4. Evaporate to leave copper sulfate crystals
• pH scale


  1 = Acidic, 7 = Neutral, 14 = Alkaline
• Acidity


  Caused by hydrogen ions
• Alkalinity


  Caused by hydroxide ions
• Acid-base titration


  1. Pipette alkali into flask

  2. Add acid from burette drop by drop

  3. Stop when indicator changes colour

  4. Repeat to get accurate result
• Indicators


  • Methyl orange (yellow to red)
  • Phenolphthalein (colourless to pink)
• Titration calculations


  1. Calculate moles of acid used

  2. Use moles of acid to find moles of alkali

  3. Use moles and volume to calculate alkali concentration
• Strong acids


  Fully dissociate into ions (HCl, HNO3, H2SO4, HBr, HI, HClO3)
• Weak acids


  Partially dissociate into ions
• Strong acid concentration


  Many hydrogen and hydroxide ions, few water molecules
• Weak acid concentration


  Few hydrogen and hydroxide ions, many acid molecules and water molecules
• Electrolysis


  Requires molten or dissolved ionic compounds