Copper plating & chrome plating titration and analysis Q&A

Hi, Komal. Please introduce yourself and try to comment in terms of the responses you've already received. Very few readers will enjoy having a stranger go on to administer this second round of a flash-card quiz to them :-)

Regards,

A. 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 A. Ammonium purpurate, more commonly known as murexide [affil links], 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 ⇦[this on eBay or Amazon or AbeBooks affil links] would be one acceptable reference. Jon Barrows, MSF, EHSSC GOAD Company Independence, Missouri

A. 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 ⇦[this on eBay or Amazon affil links] to get rid of the Fe(OH)3 before titrating. Makes the endpoint easier to see.

A. 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.

A. 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 0.1N NaOH ⇦this on eBay or Amazon [affil links] 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 [beakers on eBay or Amazon [affil links] (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.

A. Hi, Komal.

• Polyelectrolyte helps to neutralize natural repulsive charges between particles and can also help as sort of a net to get precipitates to settle.
• Lime and/or caustic soda are two primary chemicals for neutralizing acidic waste; lime is cheaper and has additional powers to help wastewater treatment but is much more difficult to reliably control than caustic soda.
• Calcium carbonate is a co-precipitant, probably unnecessary if you use lime because lime also functions as one.
• Poly aluminum chloride and alum are settling/purifying aids and in some cases improve the action of polyelectrolyte and in some cases substitute for it.
• I've never heard of amol gazol -- what book mentions it?

"Operation & Maintenance of Surface Finishing Wastewater Treatment Systems"
by Clarence Roy

on AbeBooks

or eBay or

Amazon

(affil links)

C'mon now, though, cousin! You admit that chemistry is your weak spot, and helpful readers have gently & politely told you 5 times now that in such a case you should get hold of a book on the subject lest you not even know what questions to ask with no framework. Authors spend months or years planning out their exact orders of presentation in tutorial fashion so that you can learn quickly, rather than bouncing back & forth between ideas you're not yet prepared for and stuff you've already seen a zillion times :-)

Continuing to administer this fourth round of a flash card quiz to the readers who have asked you not to isn't the best way forward :-) Chemical analysis books have already been suggested; for the waste water treatment questions I would suggest Clarence Roy's "Operation and Maintenance of Surface Finishing Wastewater Treatment Systems" ⇨
or Kenneth Cherry's "Plating Waste Treatment" (if you can find it; maybe try WorldCat.org for a library holding it)

Good luck & Regards,