Which fruit contains the most vitamin C?
Name ………………………………
Vitamin C has the chemical name ascorbic acid. This compound dissolves in water, so we can
take vitamin C into our bodies easily in a drink. In this experiment you can find out which fruit juice
is best to drink to get lots of vitamin C.
Testing for vitamin C
We can react vitamin C, or ascorbic acid, with iodine:
iodine
+
ascorbic acid

dehydroascorbic acid
+
iodide ions
+
hydrogen ions
I2
+
C6H8O6

C6H6O6
+
2I-
+
2H+
Iodine has a brown colour when in solution and iodide ions are colourless in solution.
To make the iodine colour easier to see, starch is added – this makes a blue-black coloured
complex. We can use this reaction to compare the amounts of vitamin C in different juices.
To do this, we will make an iodine solution and add juice drop by drop until all the iodine has
reacted.
 A juice with lots of ascorbic acid (vitamin C) needs a small number of drops to react with all the
iodine.
 A juice with small amounts of ascorbic acid (vitamin C) needs a lot of drops to react with all the
iodine.
What you need
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Water
Test-tubes
Test-tube rack
Plastic pipettes, one for each juice
10 x 10 cm piece of white card as background
Iodine solution
Starch solution
Eye protection
Fruit juices to test.
What you do
Put 1 cm3 of starch solution in a test-tube.
Add 5 cm3 of water. Shake the tube gently.
Add 1 drop of iodine solution. A blue-black colour will appear.
Hold the white card behind the test-tube.
Keep the white card in place - add the juice drop by drop. COUNT THE DROPS.
Stop after every five drops to shake the tube.
Keep adding juice until the blue-black colour has gone.
To check the colour has gone, write down the number of drops, then add 1-5 more. Shake the
tube again. If the colour changes, add the extra drops to the number you wrote down. Repeat
this process until there is no further change.
9. Keep the first test-tube so you can compare with others.
10. Test all juices in the same way.
1.
2.
3.
4.
5.
6.
7.
8.
Results table
Fruit juice
Number of drops needed to react with
all the iodine
Questions
1. Which juice has the most vitamin C of the ones you tested?
2. Which has the most in the whole class?
3. Why is it important to add the juice drop-by-drop?
4. How do your results compare with the information on the juice packaging?
5. What factors might affect the amount of vitamin C in the juices?