Practical investigations
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In the React website it states that it is possible to do a direct titration of aspirin using 0.10 M sodium hydroxide by crushing the aspirin and dissolving it in a known amount of ethanol. What I am asking is what procedure do you go through to gain results? Thanks for your help
Igloo writes ...
I would use a mixture of ethanol and water, rather than ethanol alone, and don’t forget that the titration should be carried out rapidly, and preferably in an ice-bath, to minimise rupture of the ester linkage by hydrolysis.
The titration reading together with the concentration (0.10 M) enables you to find the number of moles of sodium hydroxide used.
This is equal to the number of moles of aspirin present, since they react in a 1:1 molar ratio (confirm this by constructing an equation)
Knowing the volume of aspirin solution pipetted into the flask you can scale up to find the volume originally present in the volumetric flask.
This can be converted to a mass in grams, via the molar mass of aspirin, and a comparison can then be made with the mass of aspirin originally used.
You will need to think carefully about the limitations of this method (hint: will impurities such as salicylic acid interfere?)
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: 27 March 2007
