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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: JEA on September 21, 2008, 03:19:24 PM

Title: Why does adding acid in a Gravimetric Analysis of Fe2O3 matter?
Post by: JEA on September 21, 2008, 03:19:24 PM

I could really use some advice...I went back to school to take an Analytical Chemistry class after being out of school for many years (its been a REALLY long time since I had organic or general chem).

In our analytical chemistry lab our professor asked the following question:

Why is it necessary to add HCl to dissolve the FeNH₄(SO₄)₂.12H₂O?  She says it a chemical reaction question and to think what iron compound might be formed when the pH is not very acidic.

We were forming Fe₂O₃ from FeNH₄(SO₄)₂.12H₂O.  To accomplish this precipitation, we added the HCl, then the HNO₃, then heated it to get the Fe₂O₃. 

I am just lost on what type of iron compound might be formed under neutral or basic conditions and do not have basic or organic chem text to look in.  Can someone point me in the right direction....does it have something to do with Iron 2+?? 

I appreciate any direction or advice.  Thanks!

Title: Re: Why does adding acid in a Gravimetric Analysis of Fe2O3 matter?
Post by: Borek on September 21, 2008, 03:42:03 PM

If you aim at Fe₂O₃ it doesn't matter much, but think in terms of hydroxides solubility.