Practical investigations
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I have read the information but I am using aspirin tablets that will therefore have fillers/coatings etc on them so I will not know the total mass of acid present to start with. The only way I have thought of is to do colorimetry on both an unhydrolysed and hydrolysed sample to be able to measure the salicylic acid and then the total aspirin and salicylic acid and then use that data to analyse my aspirin tablets.
I know the mass of salicylic acid in a tablet should be minimal/zero but would it be accurate or fair to assume it was all aspirin and not salicylic acid that was there in the first place. This would make things much easier!!
Igloo writes
You are completely correct in thinking that there are effectively three unknowns in your analysis – the quantities of pure aspirin, salicylic acid and fillers/coatings, so a simple titration or back titration is not going to give you enough information.
Your plan to carry out titrations with unhydrolysed and hydrolysed samples will however give you the answer you are trying to find, and yes, although we often assume that the mass of salicylic acid in a “fresh” commercial tablet is likely to be insignificant, you certainly cannot assume that this is the case if you want to carry out a really accurate determination.
I’m sorry not to be able to give you the “easy” answer. However, the phrasing of your question implies that you know what to do in the circumstances, so I wish you good luck!
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: 14 October 2007
