Practical investigations
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Hi, I’m currently doing an investigation concerned with iron tablets. I want to carry out colorimetric analysis of ferrous ions and ferric ions separately in iron tablets. So far, to make the calibration graph for ferrous ions, I’ve decided to use ammonium iron(II) sulphate and potassium ferrocyanide. For the ferric ion calibration graph, I’ve decided to use ammonium iron(III) with potassium thiocyanate . However I’m not too sure what concentrations of the chosen chemicals to use, to make up the needed calibration graphs.
Ulex says
To do these calibration graphs you will need to make a guess as to what the answer is! For the iron(II) that’s easy because the packet is labelled – probably 200 mg of anhydrous FeSO4 per tablet. If you crush this up, mix with M sulphuric acid and make up the solution to a known volume, you will know approximately what the concentration is. (The Nuffield Chemistry Students’ Book has the details.) Make up your standard solutions using iron(II) sulphate which is as fresh as possible, remembering that it is hydrated, and make them with concentrations in a range which includes your estimated concentration.
For the iron(III) determination, you are on your own because you will have no idea what the answer is. You can be pretty sure that it will be a lot less than the iron(II). Take some of your ‘tablet’ solution and add some of your thiocyanate solution and see what sort of colour you get. Then try various, very dilute, solutions of ammonium iron(III) sulphate until you get a reasonable colour match and base your standard solutions around this concentration. Trial and error is the only way!
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Risk assessment
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updated: 25 January 2006
