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topic 10930

How to analyze acid level (HCL) in Ferric Chloride Solution IF there's other metal ions and carbon in the solution!


Dear Sir,

Thanks for those people whose gave me the titration methods last time, thanks you so much. But I got an other problem because the Ferric Chloride solution contained high percentage of other metal ions like copper and brass. Also contained carbon (like black dust), so can anyone tell me that is the titration method still work in this situation or I need to use other testing method to get a better result.

Albert Tsang
- England, U.K.


Dear Albert,

The only response I have to that question is as follows:

1. Can you say filtration? (sorry, trying to be funny) The carbon particulates you describe do not contribute to the titration reaction, and can easily be filtered out of solution using fluted, qualitative paper or microfiber filters.

2. It sounds like what you need to do is the same thing that I always do when I encounter an "unknown solution": Prepare standards.

3. Here's how I would prepare the standard which you describe:

a) Make up an ideal lab standard solution of the working bath. A standard which contains the optimum working agents.
b) Perform your accepted titration procedure upon this solution. Record your results.
c) Heat a known volume of the sample (in the lab) to the optimum working temperature.
d) Pass some "work" through the sample. This work should consist of brass and copper parts which you usually run. Keep a weighed, mass measurement of the parts you ran through.
e) Filter the sample, then run the same titration procedure again upon the second sample. Record results.
f) Establish a linear constant based upon the difference between the first standard and the second standard. These numbers will yield the math you need to your process control procedure.

Keep me in touch. I'm interested in your plight.


randy fowler
Randall Fowler - Fowler Industrial Plating, LLC
Cleveland, Tennessee, USA


I think now might be a good point to step back and say why am I doing this?

Why are you wanting to analyse the hydrochloric acid content?

If it is solution control a better answer might be to just go with the very simple answer of run a sample until it is not doing the process you want. Take samples every few loads (be sensible so you end with 5 to 10 samples for a bath life) Analyse these by a very simple titration NaOH and phenolphthalein (I hope I can still spell) and see if there is a pattern - do the results rise? do they fall?

If you see a pattern is it such that you can draw a line and say once it crosses that line it is time to dump the solution.

I expect many of the people will have reached the point where the lab say the solution is fine, the shop floor say it is not and when you look you find it is some contamination issue that is not tested for so the lab are right when they say they can not fine anything wrong with the solution and the shopfloor are right when they say they cannot get a good job out of it.

Testing like described above will give a robust answer and take into account the effects of the.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England

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