Practical investigations
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I'm doing my Individual Investigation on Aspirin and I'm on stuck on the preparation of Aspirin because I don't know how to work out how many grams of 2-hydroxybenzoic acid to use. Please tell me how to work it out.
Igloo writes
From the equation for the reaction, you will see that one mole of 2-hydroxybenzoic acid forms one mole of aspirin.
You now need to decide the mass of aspirin you would like to prepare. Let's assume that you would like to make about 10g of aspirin.
Next you need to find the molar mass of each of these organic molecules.
By dividing the mass of aspirin by its molar mass, you will be able to calculate the number of moles of aspirin you wish to form.
From the information in the first paragraph you can see that the number of moles of aspirin formed must be equal to the number of moles of 2-hydroxybenzoic acid required, so if this quantity is multiplied by the molar mass of 2-hydroxybenzoic acid, you will arrive at the mass of this compound required.
Do remember that the reaction will not go to completion, and that the extraction process will involve some of the product being lost during transfer processes as well as down the sink. This means that even if 10g of aspirin was what was wanted maybe only half of this will be obtained in practice. Thus if you really want about 10g of product, carry out your calculation based on a theoretical formation of about 20g of aspirin.
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: 26 February 2007
