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Author: Subject: Identification of Lead Acetate
quicksilver
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[*] posted on 2-8-2010 at 14:04
Identification of Lead Acetate


I came into possession of several bottles of unmarked chemicals. I'm having difficulty identifying Lead Acetate. Does anyone know a test for it's determination?

I frequently ask for chemicals that are going to be disposed of. Often I get some wonderful items but the other day I found some bottles that were unmarked. This is typical with free chemicals from various sources as unmarked containers often get destroyed. I determined what most of them were but this is a shame. It's white non-crystalline powder:I am fairly sure it's lead acetate but I do not remember what test I could use. I don't have access to a mp machine or other quality equipment until after Summer. In fact if there is a test for acetates in general, that would be very valuable to me.
Does anyone have a non-destructive simple test? Some things are VERY valuable today (silver salts) & getting unmarked chemicals can often be a gold mine.

In fact I have often simply worked with Merck's manual & a melting point machine or a simple reaction but a list of tests for acetates, sulfate, nitrates, chromate, & oxides would be a nice thing to study & keep. If anyone has a textbook with an exercise in it with identification processes I would appreciate the link. Because to me, with the little "gifts" I get on occasion; it would be really worth it.

Thanks.



[Edited on 2-8-2010 by quicksilver]




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[*] posted on 2-8-2010 at 14:11


Precipitate lead as PbCO<sub>3</sub>. My high school book says that acetates smell slightly of acetic acid, don't know if you'd do that with a lead salt though. Also, according to Wiki it tastes "sweetish". :)

Acidification would yield acetic acid, wouldn't it?
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quicksilver
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[*] posted on 2-8-2010 at 14:20


You're right it should (sugar of lead). I don't know if I want to taste anything I don't know: but I think you've got something with the "vinegar" smell from acidification. Good shot!



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[*] posted on 2-8-2010 at 15:41


Quote: Originally posted by quicksilver  
I came into possession of several bottles of unmarked chemicals. I'm having difficulty identifying Lead Acetate. Does anyone know a test for it's determination?


You get a discount for this as you will be doing the test
backward!

My ever useful copy of Authenrieth's Laboratory Manual for
the Detection of Poisons and Powerful Drugs, 1928.

Sez a delicate test for carbon disulpide is to add a few drops of
lead acetate solution... it will cause neither a precipitate or
color. Add excess of potassium hydroxide solution and boil.
A black precipitate (PbS) will appear.

Anyone else old enough to remember when you could
smell the chemistry building on campus 2-miles away
as every Chem 2 lab had a Kipp generator putting out
hydrogen sulphide which students bubbled through their
unknowns precipitating brown-black-yellow-white
mud depending upon the elements present?
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[*] posted on 2-8-2010 at 16:45


GpI QA test for Pb+2 is to add a chloride, like HCl. If Pb+2 is present you will get a white ppt. You can also use K2CrO4. This should yield a yellow ppt.

Consult a QA book for appropriate concentrations, etc, for the tests.

Edit: I made some aqueous lead acetate and saturated some filter paper strips with it. I use this as a sensitive test for H2S - it turns the paper black.

[Edited on 3-8-2010 by Magpie]

[Edited on 3-8-2010 by Magpie]
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aonomus
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[*] posted on 2-8-2010 at 20:05


If it is a metal salt and is water soluble, you can use qualitative identification to try to find out what it is.

Acidify with excess HCl, white ppt might indicate Pb(II), centrifuge and take that precipitate with K2CrO4, yellow confirms lead

From the supernatant, you can bubble H2S through it, or add thioacetamide with boiling to try to generate the sulfide. Resultant precipitates could indicate Pb(II) as well (but also a whole slew of other cations).

Having positive results for both tests would be indicative of either Hg(II) or Pb(II).

See also: http://www.williams.edu/chemistry/epeacock/EPL_CHEM_153/153-...
and http://www.dartmouth.edu/~chemlab/chem3-5/qual_cat/full_text...
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microcosmicus
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[*] posted on 3-8-2010 at 00:08


> but a list of tests for acetates, sulfate, nitrates, chromate, & oxides
> would be a nice thing to study & keep. If anyone has a textbook
> with an exercise in it with identification processes I would
> appreciate the link.

This book might come in handy:

A short manual of analytical chemistry: qualitative and quantitative
John Muter, J. Thomas

http://books.google.com/books?id=8MbnAAAAMAAJ&printsec=f...

As the title says, it's nice and concise. In particular, chapter 4
discusses exactly what you are up to --- how to identify an
unknown salt --- complete with instructions and tables.

> In fact if there is a test for acetates in general, that would be very
> valuable to me.

They turn red upon adding ferric ammonium chloride but lose this
color upon adding HCl. From p. 81 of the above reference.
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[*] posted on 3-8-2010 at 02:50


A very good and sensitive test for lead(II) is the formation of a very bright yellow precipitate of PbI2 when a solution of KI is mixed with a solution of a lead(II) salt.
As a second test, you can add a solution of your unknown to some dilute H2SO4. If a white precipitate is formed, this is another indication for the presence of lead(II).

If you really have lead acetate, then adding this to dilute hydrochloric acid and smelling should give a smell of vinegar. Any acetate does so.




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quicksilver
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[*] posted on 3-8-2010 at 07:11


Excellent suggestions (& books). .....Much appreciated!

I would also like to underline that I have gotten as serious amount of free items simply by asking for them & I deeply recommend that others do as well. This works especially well from assorted universities / schools (private schools are best), water treatment facilities (no kidding!), OLD pharmacies, & most any company that does metal plating (large amounts of acids).
Often you will need containers to haul away the items so it's best to be prepared. I have gotten lab equipment in various condition, enormous amounts of dry chemicals, quality solvents, and ridiculous amounts of acids. Schools & pharmacies take a bit of finesse. But metal plating companies very often have what has been called "end barrels": acids in quantities too small fora particular job and they have to have an empty (stainless steel) barrel to ship back for renewed purchase. Bringing a few gallon acid bottles will be needed.
The biggest problem is often the chemicals will have been transferred to another container with no name or the name is illegible. If offered a hot plate or something that is shabby or you don't need take it anyway with much thanks because next time they just may offer an older Zeiss microscope that they thought was trash (yep, it's happened).... With schools never say things like "I will assume all responsibility for these..." That's the kiss of death for a gift. Don't ever bring up the issue of liability. If THEY do, simply reply: "that's never been an issue in the dozens of times I've taken this junk from different people, etc".

It works & it's free. It generally a question of.... "You'll never get the sale unless you ask for it". Good hunting!


edit:
Time of day makes a difference I believe. Don't ask 1st thing in the morning or at opening; nor right at closing. A half hour before closing and right after lunch appears to be best. Smile & don't be too serious unless they are; keep it light. answer honestly that you are going to use them; don't make something up. Explain you are looking to save some money. They may want a kickback (plating shops have asked for some money on several occasions).
This also works well when asking for high voltage parts from repair shops (neon sign, microwave, & flyback transformers, etc).

[Edited on 3-8-2010 by quicksilver]




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[*] posted on 3-8-2010 at 07:31


quicksilver your anecdote about your success in asking for castoffs warms my heart. Especially since I'm assuming you live in the US.

I've been in a position to ask for these items several times but have been too timid to ask. I was afraid that this would just lead to questions about what I was doing with them and an immediate rejection based on the liability issue.

Your caution about not bringing up a problem is very wise for all aspects of life. If you have a good relationship with someone they basically trust you. If you bring up a potential problem, even in jest, you can quickly kill the deal.

For example, I was having a perfectly congenial conversation with an administrator at a university one time, asking about a former female student. Then I mistakenly said something like: "I don't want to look like a stalker...." The blood quickly drained from her face, and I cut the conversation very short. Lesson learned.
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[*] posted on 7-8-2010 at 02:16


heat a small amount in a test tube(~.1g), if its sugar of lead it will liquify and boil around 75C, do not allow the liquid to boil for more than a moment (this is the 3x waters dissociating from the acetate), put the tube aside, it should fairly quickly crystallise quite dramatically.
Reheat the tube to red heat, cool, you should have some lead powder in there, characterisable by the fact that it grey and nothing happens through succesive red heat cycles. Also it smears across paper like a lead pencil.
If this all happens then do the other aformentioned tests to confirm, if it doesn't behave in this way then your range of tests just got rather broad as there are many white powders out there, do a mp first.




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