[kellie]

Hi,

I am planning on doing a titration with EDTA to find % Zn quantitatively. So far, the brass has been dissolved in concentrated nitric, boiled off, etc. Sn was filtered out, then Cu and Pb were found by electrodeposition (well PbO2, but you see what I mean). Now for the Zn, I have 'heard' there is a method of using EDTA to find an approximate end point, and subsequent concentration etc., except that I cannot seem to find the method. Also, since there may still be trace elements in solution (namely, Cu, Sn and Pb), I was wondering if anyone knew of a good masking agent I could use.. I have heard thiosulfate perhaps, but not sure if that's the actual case. Also, if you have a reference that would be preferred but not necessary. Any help is MUCH appreciated!

;-)

[lemonoman]

I know ALL about this stuff because I did the exact experiment last term.  EXACT method.  EXACT materials.  EVERYTHING is as you describe it.  Even the objective.  And I know that course is offered again this term...and I KNOW there's a girl named kellie in it.  SO before I answer your question (the best that anyone's ever answered a question because I DID IT lol) I would like to know if this is for CHEM 224 offered at the University of Waterloo.

Seriously, I will answer your question, I'm just very curious.  What would be the odds, eh?

Hope to hear a response soon!

[kellie]

Well in fact yes, this IS for chem 224L at UW. So since you know, cough it up. ;-)

Much appreciated, and IF, you, by chance, have any idea where there would be a book maybe that I can find out that what you are about to write is right, that would just be icing on the cake!

Thanks agan,
K.

[lemonoman]

ANYWAYS

The 'masking agent' everyone talks about is a special type of indicator - Xylenol orange.  When you do the EDTA determination, there's a few more steps than with other titrations...so you have to have a procedure (hence MY problem  )

Our lab co-ordinator told me to check out a book called something like Quantitative Inorganic Analysis - It's one of those books were you just look up what you want to determine and it will give a dozen procedures on way so you can id.  I forget who it's by...the name VOGEL rings a bell though.  Check it out.

P.S. Another method to determine zinc ions in solution is gravimetry...it take even MORE steps but it is the most accurate (Not worth it if you didn't get like, 9s and 10s n the other 3 metals in the brass)

[kellie]

Thanks lemonoman!


Off to DC for me!


K.

[Mitch]

Or you could just run it through an ICP.

[lemonoman]

That's actually what else they're going to do.  They have 3 samples (which theoretically will give the same concentration of zinc).  One sample goes through an AA, and two have to be determined, "by an alternate means of your choice" and when she says that, she REALLY means titrate with EDTA or do gravimetry.

There's other ways...like one that involves cyanide or something...But some idiot a while back mixed the cyanide mixture with acid...and theh had to evacuate the lab, etc.  So they don't do that anymore.

Heck, we're not even allowed to use Nitrobenzene.  EVER.  And they call this university.