Practical investigations
Read our general notes on Risk Assessment
I have been doing an investigation to find the amount of aspirin present in a standard 300 mg aspirin tablet. I used standardised 0.1 M NaOH in my burette and an aspirin solution made up of crushed aspirin, ethanol and distilled water and an indicator of phenolpthalein. However, when I titrated equivalence was reached after less than a mL had passed through the burette! When I did my calculations, I came up with an amount of 9 mg and I am quite sure there is no error in my calculations.
Any advice would be greatly appreciated.
ThankYou
Igloo writes ...
Commercial aspirin tablets contain aspirin itself (which is of course an acid) as well as trace amounts of salicylic acid (formed by slow hydrolysis of the aspirin). Such a low titration reading can mean one or more of the following:
1. You are using NaOH of even greater concentration than 0.1 M by mistake. If you are titrating all the solution from one aspirin tablet at once, then it should require about 17 ml of 0.1 M NaOH for neutralisation. Are you sure you haven't been given 1.0 M NaOH?
2. You are not using aspirin at all, but “soluble aspirin” instead. This is the sodium salt of aspirin, so it is already neutralised.
3. If you were using “soluble aspirin” in the first place, then a low titration reading simply means that there is very little aspirin itself in the tablet, which is what I would expect. The low reading could be due to this amount of aspirin, or the salicylic acid referred to at the beginning.
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.
back to Practical investigations
Rate this page or react
Share your views on this page, 0 ratings so far
updated: 11 June 2007
