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topic 42958

Looking for a titration method for ferric chloride

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April 19, 2021

Q. I use FeCl3 solution to etch steel and a second batch of solution to etch copper. I want to analyse for free Fe and Cu respectively to decide the life of the solution. When to refresh? What is most economic method to analyse solution of FeCl3? I maintain Baumé but the presence of Fe can misguide Baumé

Kaushik Magiawala
- Chhatral Gandhinagar
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April 2021

A. Hi Kaushik. While awaiting responses, you may wish to read the earlier entries on this thread. You may also find Barlow Campano's article "Kleingarn Regenerated Spent Acid at Increasing Ferrous & Ferric Chloride Content" in our on-line reference library interesting.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
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Previous closely related Q&A's starting in:


Q. My ferric chloride etching solution consists of the following proportions:
290 grams- ferric chloride (technical grade Fe c13-6H2O)
290 milliliters- hydrochloric acid (HCl muriatic 35.6% specific gravity 1.18)
570 milliliters- water

I work in the aerospace industry and am currently changing my ferric chloride solution when it fails to etch my parts to a Kodak paper gray scale within a specified amount of time. I am looking for a simple method of testing the concentration of ferric chloride within this bath. Testing the acid concentration will not help because I use this solution to etch stainless steel. I have a titration method for two acid baths (nitric and muriatic diluted with alcohol)using 0.5N NaOH and phenolphthalein and titrating to a pink endpoint.

I would appreciate any help for finding a simple titration method.

Thank You,

Blake Hall
manufacturing - Falconer, New York
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A. Phenolpthalein is not a good indicator for your acid titration because of the high pH of 9 (plus or minus). At an alkaline pH, you are getting a false reading as metals start to precipitate out as hydroxides, using part of your titrant. I think that you can see the endpoint of methyl red ,pH of about 5. Methyl orange would probably be tough to see in a ferric chloride solution.

James Watts
- Navarre, Florida
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A. Hmmm. It's a tough problem because the acidity doesn't change, just the solution metal loading.

You could try this: take a suitably sized sample (trial and error testing would be necessary to determine this) and dilute it up to 100 ml with water, then add aq. NH3 to pH 11 or so. Filter out precipitated metal hydroxides to get a solution that should only contain the nickel. I'm assuming you're processing a stainless steel with nickel in it - most do.

Now, add some murexide indicator, and titrate with 0.1 M EDTA to a violet endpoint. This, after a simple arithmetical calculation, will give you the nickel loading, which should be correlatable to your etch test.

Or, wait a few days. Someone who actually does this type of work themselves may have a method all worked out. In that case, you should listen to them.

dave wichern
Dave Wichern
Consultant - The Bronx, New York
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A. I'm not going to look up the fudge factors, etc., but if you do an acid/base titration for HCl and a total chloride titration (titrate w/AgNO3, chromate indicator), you could then subtract out the chloride from HCl. What's left comes from the ferric chloride.

Were I in your shoes, though, I'd just use an ORP controller.

James Totter
James Totter, CEF
- Tallahassee, Florida
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June 13, 2013

A. Reduce your ferric chloride (Fe3+) down to ferrous chloride (Fe2+) using tin chloride (SnCl2). Keep adding the tin chloride until the solution turns clear. Then precipitate out the excess tin chloride with mercury chloride (HgCl). Be careful because mercury can be toxic. Add the mercury chloride to the solution until it doesn't dissolve anymore. Let this solution settle out until you have a clear liquid on top, and precipitate at the bottom.

For the titration, siphon off a known quantity of the clear liquid and titrate with potassium permanganate (KMnO4). Measure the ORP as you titrate - you should start out around 400-500 with Fe2+, and add KMnO4 until you hit 900 mV or so (Fe3+). Use the quantity of KMnO4 it took to hit 900 mV ORP as your titration quantity, and multiply the # moles of this additive by 5 to figure out how many moles of iron was in your original solution

Nate Delfino
- Boston, Massachusetts
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January 5, 2011

Q. Blake,
I don't have a response to your question, but I am interested in the FeCl3 etch solution you reference. I have some stainless steel parts that require temper etch inspection, and an etch solution very similar to the one you reference has been suggested. I would like to discuss this process.

Ed Durham
propeller systems - Columbus, Georgia, USA
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