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Ferric chloride testing

I saw some posts from 4 years ago on this subject but was wondering what the thinking is now. I need to know how to analyze for ferric chloride and hydrochloric acid % in our etchant. I'm looking for a simple titration if possible. The workers do a baumé everyday and check that. The problem is that they use the ferric for a certain number of boards and then change the solution. But if they run several thicker boards the ferric wears out sooner and they don't realize it until it gets rejected at QC and has to be remade. They would like to have the solution analyzed on a daily basis to check for depletion. Any help is greatly appreciated.

Barb Myers
Plating shop - Colorado Springs, Colorado, USA
2005

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Without knowing the composition of the solution you are analyzing, it is impossible to give a precise method. It is possible to measure Fe(III) with standard EDTA (Nitric acid interferes). You would adjust the pH of the sample solution with glycine, warm it and employ 5-Sulfosalicylic acid as the indicator. The color change is from red to pure yellow.
Determining the acid content may be a little more complicated. If there are no interferents, you should be able to do a total acidity titration using a standard base and phenolphthalein ⇦this on eBay & Amazon [affil links] indicator. Correct for the Fe(III) (1 mole = 3 moles acid) to find the HCl. I suggest you find the text by Schwarzenbach and Flaska for more information. I think the title is "Compexiometric Titrations"

Billie Joe Page
- Cleveland Heights, Ohio
2005

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2005

A method that maybe can work for you :
First analyze iron. If you have nitric acid do this :
1- Pipet 1 mL to an erlenmeyer, add 10 mL d.i. water
2- Heat to dryness on an hot plate
3- Let cool a bit and add 5 mL concentrated HCl to dissolve
solid and add 30 mL d.i. water
4- add some KI and titrate liberated iodine with
1N sodium thiosulphate ⇦this on eBay or Amazon [affil links] with starch just before the end
point
1 mL Na2S2O3 1N = 0.05585 g Fe

For chloride, you can determine it by precipitation with silver nitrate ⇦this on eBay or Amazon [affil links] . Substract chloride linked to iron (3:1)

I'm wondering too if Mohr's method do the job as :
1- 1 mL sol'n + 50 mL d.i. water
2- neutralize with ammonium hydroxide
3- 1 mL indicator (4.2% K2CrO4 + 0.7% K2Cr2O7 in d.i.water)
4- Titrate with silver nitrate 1N to red-brown end point.
Substract chloride linked to iron (3:1)

Charles Tessier
- Bromont, QC, Canada

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Hi

Can you please help me.
I need to find out how to test the Fe- Content and the HCI content in the acid pickling bath of our galvanizing plant.

Maritza Engelbrecht
Quality Controller - Steelpoort, Limpopo, South Africa
May 11, 2011