Practical investigations
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I have to find a way to determine the fruit (from my selection) which has the highest vitamin C content. I need a method that will work consistently and will display similar results throughout many tests. I also need a method which is low risk. Is there a way to find the vitamin C content without using something that could be harmful? The fruits that I think I will be using are orange, lemon, lime, pineapple, apple, banana, kiwifruit, mango, tomato, avocado. Please help.
Igloo writes ...
Of all the methods available I would recommend the one involving an iodine titration. The usual technique is to use DCPIP, but solutions of this reagent tend to deteriorate over a day or so, and need to be constantly standardised.
Make a solution of iodine in aqueous potassium iodide of a suitable concentration (about 0.1 mol dm-3) and also a solution of sodium thiosulphate accurately made up to about double this concentration, i.e. 0.200 mol dm-3. Carry out several titrations, and use the known concentration of the aqueous sodium thiosulphate to calculate the precise concentration of the aqueous iodine (one mole of iodine is reduced by two moles of sodium thiosulphate). Keep the solution of iodine in a cool place and preferably stored in a brown Winchester bottle.
Use this iodine solution to titrate samples of your fruit juices.
Refer to our vitamin C tutorial on the REACT website at
http://www.chemistry-react.org/go/Tutorial/Tutorial_22827.html
to get more practical information via our numerous FAQs on this particular type of investigation.
Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 17 August 2007
