vitamin C

• IV

  • type of fruit juice
• DV

  • volume of juice required to decolourise 1cm3 of DCPIP
• CV

  • Temperature – measure temperature with thermometer. Carry out in same place
  • Concentration of DCPIP – 1% solution used each time
  • Volume of DCPIP – 1cm³ of DCPIP solution used each time
  • Shake each tube same number of times (e.g. 3 times)
  • Same end point colour –  until the blue colour of DCPIP just about disappears
• equipment

  • 1% DCPIP solution
  • 1% vitamin C solution
  • Range of fruit juices
  • Test tubes (Version 2)
  • Pipette accurate to 1cm³
• control

  Use a 1% vitamin C solution to decolourise 1cm³ of 1% DCPIP solution
• method

  1. Pipette 1cm³ of 1% blue DCPIP into a test tube.
  2. Use an accurate pipette to add 1-3 drops of the first fruit juice to the same test tube and then shake the mixture 3 times. Continue to add drops and shake the contents of the test tube until the blue colour of the DCPIP disappears. Note down the volume of fruit juice that was used up.
  3. Repeat this procedure for the other fruit juices available. Repeats can be carried out 2 times to get mean results.
• results/calculations


  Results can be recorded in a table as well as a bar chart. Mean values should be calculated from the repeats to produce a more accurate result. 
• conclusion


   We would expect to see that different volumes of the different fruit juices are required to decolourise the DCPIP. This is due to the varying levels of vitamin C in the different fruit juices. You should see that as the vitamin C content increases, the volume required to decolourise the DCPIP decreases; a negative correlation.
• evaluation points

  • Difficulty in controlling temperature (random error) – use a thermometer beforehand
  • Difficulty in controlling temperature (random error) – use a thermometer beforehand
  • Misjudgement of end point (random error) – stop adding fruit juice once blue just about disappears