• 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
  • Note that titration is a?method of chemical analysis?that involves determining the quantity of a substance present by gradually adding another substance

Apparatus

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

Method

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 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

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

Results

• 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
• This 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