Chemistry practicals

• Independent variable


  • The thing you change
• Dependent variable


  • The other thing that changes as a result which you measure
• Control variables


  • Things that could change but we keep them the same throughout in order to ensure the results are accurate
• Always say what piece of equipment you use for each measurement, don't just say measure the length of the object
• State the flipping obvious, if you think surely they don't want me to put that, put it down anyway as you never know what marks you might pick up
• Talk about the accuracy of measurements, how will you reduce errors and uncertainties
• Do multiple or repeat measurements or readings to calculate a mean
• Write answers in bullet point format, it helps you and the examiner keep track of how many points are being made
• Use proper English, don't start going all Tarzan like saying heat liquid with fire, more like heat the water gently on a gauze on a tripod over a Bunsen burner flame
• Making salt crystals


  1. Heat concentrated sulfuric acid in a beaker

  2. Add excess copper oxide

  3. Filter out unreacted copper oxide

  4. Gently heat the solution in an evaporating basin over a water bath to get solid crystals of copper sulfate
• Electrolysis


  1. Put solution in a beaker

  2. Use two carbon electrodes, connect to power supply

  3. Positive electrode (anode) is oxidised, negative electrode (cathode) is reduced

  4. Depends on reactivity of ions in solution
• Temperature changes


  1. Carry out reaction in insulated poly-ion cup with thermometer

  2. Add other reactant, record maximum temperature reached

  3. Repeat with increasing volumes of alkali

  4. Plot lines of best fit, where they meet tells amount of alkali needed to neutralise acid
• Rates of reaction


  1. Measure volume of gas produced over time

  2. Or measure time for reaction mixture to become cloudy
• Chromatography


  1. Spot solution on chromatography paper

  2. Hang paper in beaker of water so bottom just touches

  3. Water moves up paper by capillary action, separating components

  4. Calculate Rf values to identify components
• Water purification


  Heat water in flask, collect condensed pure water
• Neutralisation titration


  1. Measure volume of alkali in conical flask

  2. Add acid from burette slowly until indicator changes colour

  3. Use moles to calculate unknown concentration
• Flame test


  • To identify metal ions
• Precipitate tests


  • To identify non-metal ions like carbonate, halides, sulfate