Practical investigations
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I am doing my A2 investigation on analysing aspirin. I’m a bit confused about the colorimetry part. Do I convert a whole tablet of aspirin to salicylic acid or is it a certain amount? I am confused on the calculations of what concentrations I should use for the calibration curve.
Igloo writes ...
In the case of a commercial tablet, providing that it is from a freshly purchased bottle, you can assume that the tablet is almost entirely acetylsalicylic acid (pure aspirin) together with inert filler material. Since the coloured complex you want to study is the one formed between salicylic acid and iron(III) ions, you are going to have to completely hydrolyse your tablet first. Then, having used colorimetry to find out the number of moles of salicylic acid, this can then be assumed to be equal to the original number of moles of pure aspirin hydrolysed. Having converted this quantity to a mass, you can then determine the percentage of aspirin in the tablet, providing this was weighed initially.
As for further practical details, you will find numerous FAQs on the construction of the calibration curve, and indeed on other aspects of the colorimetry procedure, in our tutorial 'Aspirin Investigations' to be found under 'Practical Investigations' on the Re:act Homepage.
Always carry out a risk assesment 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: 28 November 2007
