Practical investigations
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I am investigating the iron content of broccoli for my advanced higher chemistry project. I know that the vegetables must be boiled in sulphuric acid, but I have no idea how much acid to use or for how long to boil the broccoli. I feel that if I do not know these basic facts my results will be inaccurate.
Igloo says
Using sulphuric acid of a concentration greater than about 0.5 mol dm-3 is to be avoided for safety reasons, especially as you will be boiling the broccoli and there is a danger of splashing or spillage. As for the volume, use enough to cover the pieces of broccoli, and remember that you will eventually want to transfer the cooled sulphuric acid together with the iron sulphate it now contains into a volumetric flask or some other suitable container of known volume. Make sure that this liquid fits into the chosen container, so that you can eventually make up to the mark with more of the sulphuric acid. You are bound to have enough sulphuric acid present to enable a meaningful manganate(VII) titration to be carried out subsequently, so the quantity you have used will not be used in your calculations.
As for how long to boil the broccoli, you can only find this out for yourself by trial and error. Choose a reasonable time, say 10 minutes, carry out your titration, and then repeat the procedure using, for example, 15 minutes. If your titration reading is greater than before, increase the boiling time until readings remain constant.
Always carry out a risk analysis before starting any practical work, and check with your teacher.
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: 04 March 2005
