Required Practicals

• Measuring Temperature:

  • For a temperature change to be accurately measured, heat loss/gain must be minimised.
  • Polystyrene cup used to insulate solution and stirrer used to evenly distribute thermal energy.
  • Bottom of thermometer must be in the reaction mixture.
• Measuring Vol. of Liquid:

  • For analysis/titrations, a dropping pipette cannot be used as volume in each drip varies.
  • Volumetric pipette - 25cm^3 to a high precision.
  • Burettes/volumetric pipettes must be read vertically and at eye level to eliminate parallax error.
  • % error can be reduced by increasing the volume of the titre.
• Measuring Mass:

  • Weighing by difference = most accurate
  • When making a standard solution, use distilled water to wash the weighing boat.
• How can you reduce the uncertainty in a mass measurement?

  1. Use a balance with a greater resolution.
  2. Use a larger mass.
• What is the calculation for percentage uncertainty?

  (absolute uncertainty / calculated value) * 100
• What is a control variable?

  A variable that is kept constant throughout the experiment.
• Why do you use the minimum amount of hot water when dissolving a substance?

  It ensures that the hot solution will be saturated.
• Why do you allow a solution to cool to room temperature before filtering crystals off?

  If filtered at a high temperature, the yield will be lower because the solution will have a higher solubility.
• Why are crystals compressed in a funnel?

  It allows air to pass through (better drying).
• Why is a small amount of cold water poured through crystals?

  To wash away soluble impurities.
• Reagents for NO2 -> NH2:

  Sn / HCl