Practical: Vitamin C Content

• chemical name for vitamin c is ascorbic acid

  • it is a good reducing agent and therefore easily oxidised
• DCPIP is a redox indicator dye that turns from blue to colourless when it is reduced and accepts electrons

  • vitamin c is an antioxidant and therefore DCPIP is decolourised in the presence of vitamin c
  • this can be used to measure the vitamin c content of fruit juice
• IV: type of fruit juice

  DV: volume of juice (cm³) required to decolourise 1cm³ of DCPIP
• control temp

  • maintains consistent reaction rates
• control concentration of DCPIP

  • keeps reaction rates uniform
• volume of DCPIP

  • establishes consistent starting conditions
• control shaking consistency:

  • ensures uniform mixing for all samples
• same endpoint colour

  • provides a standardised endpoint for comparisons
• method

  1. pipette 1cm³ of 1% blue DCPIP into a conical flask
  2. fill up a burette with the first type of fruit juice to be used and take a note of the start value
  3. use the burette to slowly add fruit juice to DCPIP dropwise. swirl contents of conical flask with one hand whilst controlling the tap w the other
• method pt 2

  4. close the tap as soon as the DCPIP loses its blue colour and note the end value

  5. work out how much volume of the fruit juice was needed to decolourise the DCPIP

  6. repeat this procedure for the other fruit juices available. do repeats of the same juice to obtain mean results
• conclusion: volume of vitamin c solution required to decolourise DCPIP should decrease as the concentration of the vitamin c solution increases