Practical investigations
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I need a step-by-step calculation to find the amount NaOH and 2-ethanoylhydroxbenzoic acid to use in an acid - base titration for aspirin before carrying out the experiment, as I am confused as to how to do this.
I am carrying out a back titration and am using a commercial aspirin tablet. I am also carrying out a back titration between pure 2-ethanoylhydroxybenzoic acid and NaOH.
Igloo writes
(1) Assume that the aspirin tablet is 100% pure 2-ethanoylhydroxybenzoic acid. Then you can be certain that all the 2-ethanoylhydroxybenzoic acid actually present will be hydrolysed by the alkali.
(2) Weigh the tablet and then divide by the molar mass of 2-ethanoylhydroxybenzoic acid to find the moles present.
(3) To ensure that an excess of NaOH is being used, multiply the number of moles in (2) by about 3.
(4) Knowing the concentration of NaOH which you are using find out what volume contains the number of moles calculated in (3)
(5) Add this volume to your crushed tablet and heat gently.
(6) Follow the experimental procedure described in the tutorial on aspirin which you will find on React.
(7) You can adopt exactly the same procedure for an identical mass of pure 2-ethanoylhydroxybenzoic acid
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: 08 November 2007
