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I am doing an investigation to determine the concentration of iron in cereal. I liked the method on your website for extraction of iron using phosphoric acid but I am unable to determine what volume and number of moles of it to use. I have also seen method of burning the cereal to an ash then adding HCl. I want to end up with Fe2+ ions as I plan to titrate with KMnO4. Which method do you think would work best? If it is the one using phosphoric acid could you advise me on what volume and number of moles of it to use?
Igloo writes ...
I think that both methods would work well. How about using the two methods and comparing your results?
One potential problem with the “burning to ash” method is that there might be some oxidation of Fe2+ to Fe3+ so there would need to be a preliminary reduction back to Fe2+ using acid and granulated zinc. In fact, I would recommend that this granulated zinc reduction is used for all your determinations, so as to ensure that all the extracted iron is in the Fe2+ state prior to carrying out the manganate(VII) titration.
As for the phosphoric acid, the quantity used does not need to be accurately measured out. So I suggest using about 250 cm3 of a solution of 5% phosphoric acid (which contains 50 g of the acid per litre of solution) per 100 g of cereal.
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Risk assessment
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updated: 07 January 2010
