Edexcel International A Level Biology

Revision Notes

1.14 Core Practical 2: Investigate the Vitamin C Content of Food & Drink

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Investigating the Vitamin C Content of Food & Drink

  • Vitamin C is found in green vegetables, fruits, and potatoes
  • It is essential for a healthy diet
  • The chemical name for vitamin C is ascorbic acid
    • Ascorbic acid is a good reducing agent and therefore it is easily oxidised
  • Methods for the detection of vitamin C involve titrating it against a solution of an oxidising agent called DCPIP
    • DCPIP is a blue dye that turns colourless in the presence of vitamin C
    • Titration is a method of chemical analysis that involves determining the quantity of a substance present by gradually adding another substance; in this case the concentration of vitamin C is determined by gradual addition of a vitamin C solution to DCPIP


  • Vitamin C solutions
  • 1% DCPIP solution
  • Distilled water
  • Range of fruit juices
  • Measuring cylinder
  • Pipette
  • Stop watch
  • Test tubes


  1. Make up a series. e.g. six, of known vitamin C concentrations
    • This can be done by serial dilution
  2. Use a measuring cylinder to measure out 1 cm3 of DCPIP solution into a test tube
  3. Add one of the vitamin C solutions, drop by drop, to the DCPIP solution using a graduated pipette or burette
  4. Shake the tube for a set period of time using a stop watch
    • It is important to keep the shaking time the same for each concentration; this is a control variable
  5. When the solution turns colourless record the volume, in number of drops, of vitamin C solution added
  6. Repeat steps 2-5 for the same concentration twice more and calculate an average
  7. Repeat steps 2-6 for each of the known concentrations
  8. Results can be plotted as a line of best fit showing the average volume of vitamin C needed to decolourise DCPIP against the concentration of vitamin C
    • This is a calibration curve and can be used to find the concentration of vitamin C in unknown samples such as fruit juices

The DCPIP test for Vitamin C

Drops of vitamin C solution of known concentration can be added to DCPIP to determine the volume required for the DCPIP to be decolourised

Risk assessment

  • DCPIP is an irritant 
    • Avoid contact with the skin 
    • Wear eye protection


  • The volume of vitamin C solution required to decolourise DCPIP should decrease as the concentration of the vitamin C solution increases
  • The results of the experiment can be plotted on a graph of volume of vitamin C needed to decolourise DCPIP against the concentration of vitamin C
    • The line of best fit for such a graph is known as a calibration curve; unknown substances can be compared to it to gain an estimate of their vitamin C concentration
  • The calibration curve produced from this experiment can be used to estimate the concentration of vitamin C in fruit juices 


A graph of volume of vitamin C needed to decolourise DCPIP against vitamin C concentration can be used as a calibration curve to estimate the vitamin C concentration of unknown substances

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Naomi H

Author: Naomi H

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.