Gracja Kowalska          2IB



Ascorbic acid is commonly known as the vitamin C. The compound has a five-membraned unsaturated lactone ring with two hydroxyl groups attached to the doubly bonded carbons. Vitamin C  is required for the formation of intercellular material.  It is present in most of the fruits and vegetables. Deficiency of vitamin C leads to scurvy in human.  

Vitamin C is powerful reducing agent which can reduce DCPIP (2,6-dichlorophenolindophenol) and changes the colour of DCPIP solution from blue to almost colourless. The more vitamin C, the more DCPIP can be decolourized.

Research question:

What is the ascorbic acid content in fruit and vegetable fruits?


  • Independent

 type of the solution (the juice)- each trial was carried out by using different solutions intended to decolourise DCPIP solution. All solutions were prepared either by squeezing the juice out of fruits and vegetables or by filtering the juice from the carton. Obtained juices were clear and transparent.

  • Dependent

volume of the solution (needed for decolourisation) -certain volume of DCPIP is decolourised by a certain volume of ascorbic acid. Each sample of solution has different concentration of vitamin C therefore the volumes of solution needed for decolourisation of 1 cm3 of DCPIP would differ.

  • Controlled
  1. Concentration of DCPIP- the solution of DCPIP was prepared in larger amounts and the same sample was used in each trial. No changes were made to the content of the solution.
  2. Volume of DCPIP used- in each trial one constant volume of DCPIP was used so as to obtain reasonable final values. The established volume of DCPIP was 1 cm3 and it was controlled by using the same pipette (1cm3 ±0.05) to measure needed volume of DCPIP.
  3. Type of equipment- each measurement was carried out using the same apparatus. Example: the DCPIP solution was measured using only one same pipette throughout the experiment
  4. State of the decolourisation- as the experiment bases visual aspects, one sample of decolourised DCPIP was used as the basic one and later on each test tube (containing DCPIP and certain amount of juice) was compared with the basic one. The state (the colour) of decolourisation was supposed to be the same in both samples.
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  • 5 test tubes (20cm3 each ±0.5cm3)
  • 2 pipettes (10cm3 ±0.5)
  • Pipette (1cm3 ±0.05)
  • DCPIP solution
  • Ascorbic acid solution (concentration 0.1%, 500cm3 ±1)
  • Bottle of distilled water
  • 8 filters
  • Fruit press
  • dropper


  1. Label the test tubes, then slowly pipette 1 cm3 of DCPIP into each test tube.
  2. Take 5 cm3 of 0.1% ascorbic acid using the pipette.
  3. Add the o.1% ascorbic acid drop by drop into the first test tube, gently shake the tube after each drop is added. As soon as the DCPIP becomes decolourised, ...

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