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Analysing results from the vitamin C experiment

In the previous step we performed an experiment that measured the amount of vitamin C in fruit or vegetable juice. Now that we have some data from the experiment, we need to analyse it to work out what it means.

From our calibration experiment in the previous step it is possible to work out the amount of vitamin C that is detected per drop of iodine solution. Once you have calibrated the number of drops of iodine that relate to each milligram of vitamin C, then you can work out the number of milligrams of vitamin C in a known quantity of your juice. For example, once you have measured the number drops of iodine to see a stable colour in a set volume of juice, you can work out how much vitamin C is in that volume. To do this you take your known amount of vitamin C per drop of iodine solution and multiply it by the number of drops of iodine required to see a stable colour in the juice.

It is then possible to scale up your answer to volumes that are more standardised, such as the litre. For example, if your answer was something like 5.3 mg of vitamin C in every 50 mL then we can say that there are (1000/50) x 5.3 mg per litre of juice. In this case the unknown has 106 mg vitamin C per litre of juice.

If you have measured out the calibration solution and your unknown in the same pot but you do not know the exact volume of the pot we can do the calculation slightly differently. Let us say, for example the concentration of vitamin C in your known sample was 1000 mg per litre. Let us also assume that 120 drops of iodine were needed to produce a stable colour in one measure of the calibration solution but only 8 drops were required for the unknown. We work out the concentration of the unknown by multiplying the ratio or the number of drops by the concentration of the calibration solution (8/120) x 1000 mg. In this case the unknown has 66 mg of vitamin C per litre of juice.

Having reviewed this experiment and the way to analyse the data, feel free to post comments and discuss your results.

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This article is from the free online course:

Biochemistry: the Molecules of Life

UEA (University of East Anglia)