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IODINE SOLUTION

This procedure is referred to as standardisation – you are said to standardise the iodine

solution. The accurate Vitamin C standard solution is prepared by dissolving pure Vitamin C

(ascorbic acid, a white powder) in water using a volumetric flask.

In Part Two once you have confirmed the iodine solution concentration you can use it to

determine the unknown concentration of Vitamin C samples. These could include Vitamin C

tablets or fruit or, in this case, apple juice. This is the method by which the concentrations of

many species of interest in many different samples may be determined.

The apple juice container advertises how much Vitamin C is present in the drink. You should

be able to determine whether this assertion is correct.

Chemistry connections…

In 2004, two school students in New Zealand performed redox titrations on several brands

of juice and cordial to determine their Vitamin C content. In their school laboratory they

discovered that the cordial drink Ribena did not contain the advertised Vitamin C content.

The manufacturer GlaxoSmithKline ended up in court facing charges of over two million

Australian dollars because of their find.

Foundations of Chemistry Laboratory Manual VITAMIN C DETERMINATION 3F

4

In general; as long as you know the concentration of one reactant (in this case the iodine

solution) you can use it to determine the concentration of the other (in this case the Vitamin

C content of commercial sources).

Experimental

Remember: drawing a diagrammatic representation of what you will do in your experiment

can help you to visualize what you’ll need to do during the session and also to not

accidentally miss crucial steps.

Before commencing work you should watch the video, ‘Solution Preparation’. You will need

to equip yourself with headphones and wait until your colleagues are ready before asking

your demonstrator to start the video.

Reminder – each student should work individually. It is important that you work carefully in

order to gain worthwhile experience from this class.

Hazardous substances

Iodine I2 toxic, irritant

Starch (C6H10O5)n irritant