practical 1

• describe a method to produce a volumetric solution

  1. weigh the mass of solid in a weighing boat and transfer to the beaker
  2. reweigh the weighing boat and record the difference in mass
  3. add distilled water and stir with a glass rod until the solid has dissolved
  4. use a funnel to transfer the solution into a volumetric flask with washings
  5. make up to 250cm3 with distilled water so the bottom of the meniscus sits on the line
  6. stopper the flask and invert (shake)
• describe a method to determine the concentration of a solution by titration

  1. fill the (clean) burette with solution of known concentration
  2. use a (clean) pipette to measure and add 25cm3 of solution with unknown concentration to a conical flask
  3. add two to three drops of phenolphthalein
  4. titrate the solutions, slowly adding the solution from the burette and swirling the flask gently on addition
  5. add the solution dropwise around the end point
  6. record the volume of solution added to neutralise
  7. repeat until you get two concordant results and calculate a mean titre
• how could you reduce uncertainty in measuring mass?

  • use a more accurate balance
  • use a larger mass of solid
  • weighing by difference
• why do the washings need to be added?

  ensures all the solution is added (reduces loss) so that the accurate concentration is recorded
• why does the flask need to be inverted and shook?

  to mix the content to ensure a uniform solution with all contents dissolved
• how could you reduce uncertainty in titrations?

  • use pipettes and burrettes instead of measuring cylinders as they have lower apparatus uncertainty
  • increasing volume/conc of solution in flask or decreasing volume/conc of solution in burette
• how are the buretter and pipette cleaned and why is this necessary?

  they are washed with a small volume of the solution they are being used to measure, this removes any impurities so that the concentration is not affected
• why should only two to three drops of phenolphthalein be added?


  any more would make the colour change difficult to see
• why should the flask be swirled gently?


  ensures the solution is mixed so all reactants react and a precise end-point in recorded
• why should the solution be added dropwise around the end-point?


  so that a precise end point is recorded and the titration is not 'over-shot'
• what does concordant mean in terms of titre values and why is it important?

  results within 0.1cm3 of one another, this means the titration technique is consistent

  this means an accurate and confident mean titre can be calculated