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"Titration for Sulphuric Acid in Anodizing Bath"

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Current question:

Ed. note: Please!
No abstract questions.
Huh?

November 28, 2021

Q. Dear sir,

Many thanks for easiest method of sulphuric acid titration for anodizing. So please give regular updates regarding this type of method.

Best regards,

Sandeep Dedania
Engineer - Rajkot India
^


December 24, 2021

A. Hi Sandeep
I've posted the exact titration and calculations here before, and can't recall them away from my desk, but look around the site history and you will surely find them [Ed note: here's that link]. The biggest issue is knowing how to separate straight acid-base without the dissolved aluminum (And other hydroxide forming compounds) interference. You will always need to do 2 titrations to tease them out. If you get this message before you figure it out, reply and I will send better instructions when I'm at my lab.
Cheers.

Rachel Mackintosh
Lab Rat and some other things - Greenfield
^




Closely related Q&A's, oldest first:

2000

Q. When one is sulfuric acid anodizing, say, at the concentration of 165 gr/liter, does that mean for every liter if solution, there is 165 grams of sulfuric acid? Or does that mean that the 165 grams of acid is added to one liter of water? I'm a little confused over this issue.

Thank you,

Marc Green
Marc Green
anodizer - Boise, Idaho
^


simultaneous 2000

A. The former is correct, 'grams per liter' mean grams per liter of total solution, NOT grams PLUS a liter.

For those chemists in the crowd, remember the problems you had when first introduced to Molar vs. Molal? For the uninitiated, Molar is moles per liter, Molal is moles plus a liter. And we're not talking about groundhogs!

bill vins
Bill Vins
microwave & cable assemblies - Mesa (what a place-a), Arizona

^


2000

A. Marc,

To answer your question, it means 165 g contained within the volume of 1 liter, not added to 1 liter.

For instance if you wanted to make a 1 liter solution of 165g/L sulfuric acid and the acid you had on hand had a specific gravity of 1.84 g/mL (the usual "concentrated" sulfuric) you would do the following:

Using an appropriate container accurately marked to show 1 Liter add about half the water needed, then very slowly and carefully add the acid (89.7mL = 165g). When that cooled down then the rest of the water would be added to adjust the level to the 1 Liter mark.

Paul Stransky
- Putnam, Connecticut
^



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



2000

Q. I've really enjoyed the feedback from this site, I've found all of your answers very informative. Now I have another titration question. Do you guys have an opinion as to which Sulfuric acid titration is the best (for a standard anodizing tank)? I think I've tried 3-4 of them, and had varying (slight) results. I prefer using a potential titration, as I've found that the colormetric titrations vary, as each individuals perception of colors is different.

I was also wondering if any of you had used a piece of equipment that is supposed to be able to calculate the exact square footage of work being place in the anodizing tank, and adjusts the amperage accordingly. As we are a job shop, we run numerous shapes and sizes of parts at the same time, and calculating the surface area can be cumbersome, and inaccurate...so we just end up anodizing by voltage, which I know isn't the correct way to do things. We do spend the time to calculate surface area for our hard anodizing..but the decorative work has always been a pain to figure out.

Once again, thank you for all your input.

Marc Green
Marc Green
anodizer - Boise, Idaho
^


2000

A. A titration with a very good probe and meter will be the easiest to replicate. If you are testing for aluminum, then you are adding fluoride in an excess, which is hard on a conventional glass bulb probe and very hard on an analytical one. There are high quality probes made that will stand up to short term fluoride. Most are solid. They are not as cheap as low end probes, and are about on a par with high quality ones.

Titration with indicators is not all that bad if all of the operators are trained by the same person and not allowed to do the test until certified by the trainer. Consider taking a picture of the endpoint with a macro (close up) lens, having several prints made and issuing one to each person with a couple in reserve.I have never heard of a practicable and affordable way to estimate area. By keeping a log of the calculated area by part number, you should have about 90% of your parts as a known.

James Watts
- Navarre, Florida
^


2000

Q. Thanks for replying, James..I am testing for aluminum content, as well as sulfuric concentration..but am not using fluoride..I'm just using 1N NaOH to a pH of 3.6 (for sulfuric concentration) and then carrying the titration to a pH of 8.5 for the Al content (subtracting, and multiplying by 1.8)

I do use methyl orange, and phenophatlien for indicators, just to know when I'm getting close to my desired endpoints. I believe we are using a quality meter, its an Accumet..and it was a spendy sucker, so I'm assuming its a good one, its quite consistent. I am curious about using fluoride, if you had a minute to detail that method for me, I'd appreciate it.

Thanks,

Marc Green
Marc Green
anodizer - Boise, Idaho
^


2000

A. The way I always did this analysis was to titrate a 2.00 ml portion of sample to a phenolpthalein endpoint, both alone, and with a 5 ml portion of 10% potassium fluoride added. A blank titration also needs to be run on a mixture containing just the potassium fluoride. This volume is subtracted from the volume used in the second titration above. Values for total acid, "free" sulfuric acid, and aluminum can then be calculated. It's important to be consistent in the rate of addition of the titrant, and endpoint recognition. My rule of thumb was always to titrate slowly to a pink endpoint that persists for at least 30 seconds.

I have also done a titration for just aluminum using a more elaborate procedure when a more accurate result was needed. An excess of EDTA standard solution is added to a diluted portion of sample, the pH lowered to less than 2 with HCl, and the mixture boiled for 5 minutes. Then, ammonia is added to a pH of about 9, PAN indicator added, and the excess EDTA titrated away with a standard copper solution. This procedure is tricky but can yield very good results with a little practice.

dave wichern
Dave Wichern
Consultant - The Bronx, New York
^



2001

Q. What % of water is in sulfuric acid when the specific gravity is 1.25?

Joan Kress
- Patchogue, New York
^


November 2021

A. Hi Joan. It's 1/3 acid 2/3 water, but you can easily Google "specific gravity vs. sulfuric acid concentration" and have the answer for every specific gravity rather than just this one.

But because you have posted on a thread about sulfuric acid in anodizing solutions, and in case you are referring to an anodizing bath, it's important to warn you that dissolved aluminum will render this approach meaningless after initial make-up.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



2004

Q. Hi there

I am student and am also attempting to do a similar analysis on the amount of aluminum and sulphuric acid in water from an anodising bath.

Could you please tell me what the Potassium Fluoride does in this titration, and how these calculations are actually done?

Cheers

Erin Fong
- New Plymouth, New Zealand
^



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



2006

Q. Hello finishing.com world. As you may already know, I've been working on my small Type II anodizing business for nearly two years now. I'm finally anodizing like crazy and having a ball doing it! We're mostly doing custom work (multi-color stuff) and things are going well and this is mostly in part to you folks who have aided me so much throughout this entire journey. It is you people I thank!

As my business has been completely funded out of my own personal bank account (with some help from my brother's custom machine shop), I still haven't been able to get together the funds to purchase the textbooks I've been so desperately wanting (The Surface Treatment and Finishing of Aluminum and Its Alloys). As a result, most of my questions have been answered here at finishing.com or other smaller "do-it-yourself" forums. Today is no different from any other day I drop by...I have a question.

I am having a difficult time finding the procedure for titrating my electrolyte tank. Obviously I want/need to be able to check the acid and aluminum levels. I may have come across something and have been playing with it with some decent results. Below is my method of titration, apparatus and calculations utilized. Does this look anything like the right method to all you pros? Any and all help is greatly appreciated!


Apparatus & Reagents Required
0-50 ml buret
400 ml beaker
250 ml graduated cylinder
pH Meter
NaOH 1.0N (sodium hydroxide)


Procedure
1. Fill buret with NaOH 1.0N (sodium hydroxide)
2. Measure 200 ml of DI water with graduated cylinder and pour measured amount into 400ml beaker.
3. Pipette 5 ml of electrolyte solution into beaker.
4. Insert pH meter into beaker.
5. Slowly add NaOH from buret into beaker until a pH reading of 3.6 is reached. (Constant stirring required)
6. Record reading on buret as Value A.
7. Slowly add NaOH from buret into beaker until a pH reading of 8.5 is reached. (Constant stirring required)
8. Record reading on buret as Value B.

Calculations
g/l H2SO4 (sulfuric acid) = Value A x 9.8
g/l Aluminum = (Value B - Value A) x 1.8

Or allow me to rephrase the question :

What is required, what is the process and what are the calculations for titrating the electrolyte in a type II anodizing line?

Thanks!
- Dan

daniel degueldre
Daniel DeGueldre
anodizing shop entrepreneur - Ste. Anne, Manitoba, Canada
^


2006

A. Hi Daniel,
The free sulfuric acid determination is correct.
Endpoint 'B' is usually at pH 10.0 (pH 8.5 corresponds to a phenolphthalein endpoint; the difference in mls is very small).
Aluminum content is [Al] = (B - A) x 1.35, g/L

Ken Vlach [dec]
- Goleta, California

contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

^


simultaneous 2006

A. The way I always did it was as described in the "Metal Finishing Guidebook and Directory." Briefly:

Combine about 100 ml water, 5.0 ml electrolyte, and a few drops phenolpthalein indicator solution. Now, titrate with 1.0 n NaOH to a pink endpoint that persists for at least 30 seconds (important!) and record the ml. titrated.

Now, repeat the above procedure, but also add 10 ml 10% potassium fluoride solution. A precipitate will form on this addition - that's AlF3. What you're doing is preventing the titration from "seeing" the acidity from the dissolved Al. Again, titrate as above, and record the ml. titrated.

Al (oz/gal) = (vol in first titration - vol in second titration) x 0.24

Total Acid (oz/gal)= vol in first titration x 1.308
Free Acid (oz/gal)= vol in second titration x 1.308

Your procedure may work as well - I can see why. But I always did it as above and never had any problems.

Good luck!

dave wichern
Dave Wichern
Consultant - The Bronx, New York
^


2006

thumbs up sign Thank you Ken. You have been a tremendous aid!

- Dan

daniel degueldre
Daniel DeGueldre
anodizing shop entrepreneur - Ste. Anne, Manitoba, Canada
^


2006

A. I had to dig out one of my reference books for this, Volumetric Analysis of Metal Finishing Solutions [affil. link to book on Amazon], by Andrew McFadyen (Finishing Publications, Ltd., Stevenage, UK, 1998). McFadyen gives the following:

To a 250 ml flask pipette a 2 ml sample and add about 100 ml DI water. Add 1g KF and 1ml thymol blue indicator and dissolve. Titrate with 1.0N NaOH to a permanent blue endpoint, record mls NaOH used as A. g/l free sulfuric acid = 24.5 x A.

Repeat the above, but do NOT add the KF; record the volume of NaOH used as B. g/l Al = (B - A) x 4.5

The purpose of the KF is that it binds up the Al which will interfere with the sulfuric acid determination.

This ain't to say your way is incorrect; it's probably okay. The theory is that you are determining free and total sulfuric acid, and the difference is due to the Al.

James Totter
James Totter, CEF
- Tallahassee, Florida
^


2006

thumbs up signThank you for the help all. Very much appreciated!

- Dan

daniel degueldre
Daniel DeGueldre
anodizing shop entrepreneur - Ste. Anne, Manitoba, Canada
^



2007

Q. Hi everyone
Thanks for this wonderful site
I want to determine the Al2O3 and SiO2 percentage in a mineral containing SiO2, Fe2O3, Al2O3.K2O, Na2O
I have no apparatus in my lab and I need volumetric analysis not gravimetric.
Please if you can support me with calculation I will be thankful.

Adam [last name deleted for privacy by Editor]
- Cairo Egypt
^


thumbs up sign Hi Adam. Anyone is welcome to answer you, but this site focuses on metal finishing not mineralogy, and you posted on a thread about analysis for sulfuric acid in anodizing so, apologies, but it's unlikely that qualified people will see your question :-(

Luck & Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



May 18, 2009

Q. Hi All,
I am finding difficulty in detecting the end point in EDTA back titration for alumina, please guide me.

THANKS,
LEENA

LEENA PANCHAL
CHEMIST - INDIA
^


November 2021

A. Hi Leena. Well, Dave did warn you above that it's tricky and requires practice :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^

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