Re: Tests for Fe+2 and Fe+3.....

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From: SFPhysics@aol.com
Date: Tue Feb 29 2000 - 14:52:15 PST 

From: SFPhysics@aol.com
Message-ID: <32.1d2198d.25eda79f@aol.com>
Date: Tue, 29 Feb 2000 17:52:15 EST
Subject: Re: Tests for Fe+2 and Fe+3.....

> Dear chemists,
> A student of mine is doing a science fair project on "bio-rusting". We are
> having difficulty finding a method which will detect rust in water. We
> have tried ferricyanide, ferrocyanide and KSCN with no results. Can any
> one suggest other methods or offer suggestions?
> Thank you, Yibi Smith, Dixon High School
>>

Greetings Yibi:

I am no chemist but we did look at metal ion contaminates in my "Chemistry in
the Community" classes and years ago when I taught Chemistry.

The potassium thiocyanate (KSCN) tests for the presence of Fe+3 ions which
you should find in water when Fe3O2 is in solution. The color of the complex
should range from light pink to red to almost black. This is a *very*
sensitive test and will show Fe+2 and Fe+3 with only a few parts per million.

Now, either your KSCN test solution has been contaminated or your solution
being tested is contaminated or really has *NO* iron. Take a large beaker
full of water and drop in 1 drop of ferric chloride. Put in 10 drops of
KSCN, it should show you a definite dark red reaction. If not, your KSCN is
somehow defective. Any presence of Fe ions will give you:

Fe+3 [aq] + SCN- [aq] --------> Fe(SCN)2+1 red color!

When something does not work in Chemistry, my experience is that at least one
reagent solution has been rendered useless by contamination. Teaching
Integrated Science last year at Mission taught me that those neat little
plastic chemical reagent bottles are used by students to suck up solutions in
the manner of an eye dropper. Results after that are garbage and cleaning
the plastic bottle droppers of contamination is miserable.

Remember to use controls. One solution should have a known Fe+3 content and
one should be distilled water. Controls tell you whether your experiment is
on track or not. You might even wish to make serial dilutions to give you
varied concentrations that will indicate how much iron is present by the
color intensity. Then, using your test sample and comparing it will give you
an idea of Fe+3 concentrations.

Best of luck, let us all know how you do resolving this,

Al Sefl

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