Test for Vitamin C - titration

Place the fruit juice you are examining in the burette and ensure the meniscus of the fruit juice is on a measurement line (e.g. 100ml).

Measure out a known quantity of DCPIP into a conical flask and stand this under the burette on a white tile (this is so that you can see any colour change easily).

First carry out a rough titration - gently swirl the conical flask while you add fruit juice to it from the burette. As soon as you see the colour change (blue-purple to pink to clear), turn off the tap on the burette and note down the volume of fruit juice you added.

Now repeat the experiment, but this time as you get near the end point (the volume you added last time) slow the burette flow down until you are adding the juice drop at a time.

As with all experiment, repeat your readings to check for anomalies and remember you should never include the rough reading at the start in your calculations.

Here are two suggestions of what you could do with this data:

1. If you know the concentration of the DCPIP (the school technicians should be able to tell you), you can work backwards using the titration calculation to find out the concentration of vitamin C in the juice.

2. If comparing different juices, you could look at the volume of juice you had to add to make the DCPIP change colour. For example, if it takes twice as much orange juice as cranberry juice to change the colour of DCPIP, then the sample of orange juice you had has half the amount of vitamin C as the sample of cranberry juice you had.