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Electrolyte titration questions for copper and chrome plating

June 9, 2010

1) Why Methyl orange indicator is used in the titration to find conc. of H2SO4 in copper plating electrolyte ?
2) Why Ammonium bifluoride is used in the titration to find cons. of chromic Acid in Chrome plating electrolyte ?
3) Why potassium iodide is used in the titration to find cons. of chromic Acid in Chrome plating electrolyte ?
4) Why starch is used in the titration to find cons. of chromic Acid in Chrome plating electrolyte?
5) Why H2SO4 is used in the titration to find cons. of chromic Acid in Chrome plating electrolyte?

KOMAL KUMAR
plating shop employee - Rudrapur, Uttarakhand, India

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You really need a good book on the subject. Methyl orange is used because or the pH that it changes color is low enough that you will not precipitate metal ions. Phenolphthalein is the normal high school chemistry indicator, but at that high a pH, you will precipitate most of the metals in the sample solution and will have a terrible answer. The fluoride will tie up any aluminum in the solution. Starch is used as you near the end point because it is a good color change. It is a very difficult endpoint that few can do without the starch. It is visual endpoint is massively complicated if there are other trash metals in the solution if you do not use the starch. Follow the instructions. They were developed by talented people. James Watts - Navarre, Florida 1) The methyl orange color change occurs at a convenient pH for the determination. There are others you could use that change color at a similar pH, but methyl orange is the one that is typically selected 2) Ammonium bifluoride masks the dissolved iron in the solution and keeps it from interfering with the titration. 3) The determination is based on a class of titrations called iodometry. In this case, chromic acid reacts with excess iodide to produce an anione called triodide. The triodide is then titrated with the thiosulfate. 4) The starch indicator makes the endpoint easier in all iodometric titrations. 5) Acid is also consumed in the reaction from iodide to tri-odide. It just needs to be in significant excess. The best book explaining the details of the analysis of chrome plating is by by Terrance Irvine, The Chemical Analysis of Electroplating Solutions. I wish that I still had my copy. I'm sure it is out of print, but you can probably find it used. Jon Barrows, MSF, EHSSC GOAD Company Independence, Missouri

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June 11, 2010

1) why ammonium solution, ammonium purpurate and EDTA are used to find the consentration of CuSO4 in copper plating electrolyte?

Komal Kumar
- Rudrapur, Uttarakhand, India

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June 14, 2010

Hi, Komal. Please try to introduce yourself and reply in terms of the responses you've received. Few readers enjoy being flash-card quizzed by a stranger :-)

Regards,

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

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July 2, 2010

I'm so thankful to Mr. James Watts & Mr. Jon Barrows
to provide the answers of my questions actually I work for plating shop but chemistry is not my strong subject.
please provide the answer of my previous question.

Komal Kumar
- Rudrapur, Uttarakhand, India

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Ammonia is used for complexing the copper ion so you have less interference from ions like iron. EDTA is a better complexer, so it will pull the copper from the ammonia complex. It also is a terrible end point to find if you do not have an indicator. The indicator that you mention also has a couple of trade names as well as a very specific chemical name. As in my first post, you need to get a book on chemical analyzes of plating solutions. A college chemistry book would not hurt also. James Watts - Navarre, Florida Ammonium purpurate, more commonly known as murexide, is just an indicator that is common for complexometric titrations involving EDTA. The indicator, when bonded to the free metal ion in your solution, will be purple. When you titrate, the EDTA forms a more favorable complex with the metal ion and displaces the indicator from its complex. When all of the indicator has been displaced by the EDTA, you visually see the color change as a disappearance of purple. If it is important for you to understand these basic mechanisms of your titrations, then I would suggest you get a used textbook in quantitative chemical analysis in addition to the book that I have already mentioned. Older editions of textbooks can be found for very little money. Daniel C. Harris, 4th or 5th edition would be one acceptable reference. Jon Barrows, MSF, EHSSC GOAD Company Independence, Missouri

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July 20, 2010

I generally use PAN as an indicator in EDTA titrations of copper solutions. Nice, sharp endpoint.

It is helpful to, after the addition of the ammonia, to filter through Whatman #4 to get rid of the Fe(OH)3 before titrating. Makes the endpoint easier to see.

Dave Wichern
Consultant - The Bronx, New York

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July 30, 2010

I'm again thankful to Mr. James Watts & Mr. Jon Barrows
to provide the answers of my questions.

I have two more Questions Related with Nickel electrolyte titration.

1)why potassium chromate solution and silver nitrate solution are used to find the cons. of NiCl2 in Nickel plating electrolyte?

2)why mannitol powder, bromocresol purple and NaOH are used to find the cons. of Boric Acid in Nickel plating electrolyte?

Thanks in advance

Komal Kumar
- Rudrapur, Uttarakhand, India

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August 3, 2010

Komal-
You really need to get some of those reference books...
1) Silver reacts with chloride ion to form an insoluble silver chloride which is a white precipitate that is seen as cloudiness. The silver also reacts with chromate to precipitate a red-orange silver chromate, but the reaction with chloride is thermodynamically favored which causes the chromate reaction to be put on hold until there is no more chloride left in the solution. So, once you see the permanent darker color in the precipitate begin to form, you know that your titration is complete.
2)Boric acid is a weak acid which means that it doesn't dissociate very well into acidic hydrogen cations and a borate anion. In order to perform an acid-base titration between boric acid and NaOH, we need to have acidic hydrogen ions. Mannitol is just the thing that gives that to us. It reacts with the boric acid to fully free up one of the three hydrogens in boric acid. We then titrate that free ion with NaOH. Bromocresol blue is just a color indicator that changes when the pH is high enough to signal that the reaction between the H+ and the OH- is complete. Good luck.

Jon Barrows, MSF, EHSSC
GOAD Company

Independence, Missouri

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August 5, 2010

A side note to what Jon said. Make a solution of boric acid in DI water and let it set overnight. Very slowly titrate a sample of this with a 0.1 NaOH solution with a pH meter. on the graph you will see 3 fairly distinct inflection points in the curve where each H comes off. In titrating the boric acid in the nickel solution, most of us go too fast and would drop out some of the nickel which would give a very false analysis. As Jon said, the manitol frees up the first H ion and it can be titrated reasonably rapidly. As you should have noticed, care must be taken to exactly duplicate an analysis. Ie, do not rush it. I used a tiny spin bar in a small beaker(25 mls) at a fairly high speed and a slow drip of the hydroxide. The great part about this analysis is that it does not have to be ultra accurate. Close is good enough.

James Watts
- Navarre, Florida

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September 21, 2010

Hi,
I have a question related Effluent treatment.
Why below given chemicals are used in effluent treatment and how work individually?
1) polyelectrolyte
2) lime
3) calcium carbonate
4) poly aluminium chloride
5) alum
6) caustic soda
7) amol gazol

thanks

Komal Kumar
- Rudrapur, Uttarakhand, India

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September 21, 2010

Hi, Komal.

C'mon now, cousin. You say that chemistry is your weak spot, and people have gently told you five times now that in that case you need to get hold of some books on the subject rather than expecting a daily personal tutoring :-)

I would suggest Clarence Roy's "Operation and Maintenance of Surface Finishing Wastewater Treatment Systems" [affil. link to book on Amazon] or Hartinger's "Handbook of Effluent Treatment & Recycling for the Metal Finishing Industry" [affil. link to book on Amazon]. Good luck.

Regards,

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