Experiment 7 The Gravimetric Determination of Iron in a Commercial Unknown

Experiment 7 The Gravimetric Determination of Iron in a Commercial Unknown 

Obtain a sample from your instructor. Record the unknown number and dry as discussed in Experiment 6 and in Section 3.7. Also, obtain and prepare two porcelain crucibles and lids, as done 

Add 5 mL of distilled water and 10 mL of concentrated HC1 to each beaker, and place stirring rods in the beakers and watch glasses on them. 

Place the beakers on a hot plate in a good fume hood and bring to boiling. Allow to boil about 2 min to ensure complete dissolution. 

When the samples are completely dissolved, remove them from the hot plate and, while they are still in the fume hood, add 100 mL of water. Then remove from the hood and add 2 mL of concentrated HN03. (Be sure not to lose any yellow solution that might be adhering to the watch glass.) The purpose of the nitric acid is to ensure that all of the iron is present as Fe3+ and not Fe2+. 

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