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Author Topic: Chemical Identification of an unknown alkali  (Read 52917 times)

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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #60 on: January 10, 2008, 04:46:39 AM »

Borek, forgive me of my ignorance. I have to admit that my chemistry is poor.  Thanks for explaining the essential basics.  I understand now why strong acids can't be determined by titration.  For the latter question, sorry diluting strong acid should raise the pH. By the same principle, is it still not possible to use titration because the strong acid is still fully dissciated?
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Borek

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Re: Chemical Identification of an unknown alkali
« Reply #61 on: January 10, 2008, 06:29:05 AM »

Borek, forgive me of my ignorance. I have to admit that my chemistry is poor.  Thanks for explaining the essential basics.  I understand now why strong acids can't be determined by titration.

Two separate things, which you are mixing now - perhaps your thnking is OK, but wording is wrong. You can use acid/base titration to determine AMOUNT of strong acid, you just can't use titration to determine its pKa.

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For the latter question, sorry diluting strong acid should raise the pH. By the same principle, is it still not possible to use titration because the strong acid is still fully dissciated?

See above - you can determine amount (although if the concentration is too low titration is of no use). You can't determine pKa, reason (full dissociation) remains the same regardless of the concentration.

Note: reality is a little bit more complicated, but it doesn't change the outcome - you can't use titration for pKa determination for strong acids.
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Alpha-Omega

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Re: Chemical Identification of an unknown alkali
« Reply #62 on: January 10, 2008, 10:02:06 AM »

Analytical Chemistry is analytical chemistry ...the way Forensic analysis differs from the usual is the CHAIN OF CUSTODY.

The Chain of Custody in Forensic distinguishes what happens during the analysis process....Every thing done to sample must be cataloged and documented...that includes a signature for every finger that touches a sample...

Let me see what I can find for you....
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Alpha-Omega

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Re: Chemical Identification of an unknown alkali
« Reply #63 on: January 10, 2008, 10:23:05 AM »

AHHH Seek and ye shall find.  Here you go:  http://www.forensicpage.com/new25.htm
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #64 on: January 10, 2008, 12:27:24 PM »

 http://www.forensicpage.com/new25.htm:  No test method in this homepage.  The  Reference Manual on Scientific Evidence
link there doesn't work.  What is AHHH?  Thanks!
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Alpha-Omega

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Re: Chemical Identification of an unknown alkali
« Reply #65 on: January 10, 2008, 01:20:01 PM »

http://www.forensicpage.com/new25.htm

Go to Trace Evidence Recovery Guidelines
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Alpha-Omega

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Re: Chemical Identification of an unknown alkali
« Reply #66 on: January 10, 2008, 01:22:09 PM »

http://www.fjc.gov/public/pdf.nsf/lookup/sciman00.pdf/$file/sciman00.pdf

here is the PDF Reference Manual on Scientific Evidence...
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #67 on: January 10, 2008, 01:56:47 PM »

Seems there are no standard methods for acid base identification in the website?!
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Alpha-Omega

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Re: Chemical Identification of an unknown alkali
« Reply #68 on: January 10, 2008, 02:06:54 PM »

I would not think there would be...they would use methods from ASTM or EPA or USP/EP/JP/ACS...and they have to be documented to work...then they apply their chain of custody to those methods....

The species you are looking at...they would apply a quantitative intrumentation method to...like IC...something that has documentation behind it to show it is a validated method.
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #69 on: January 10, 2008, 04:08:41 PM »

You showed me ASTM, EPA.  what is USP/EP/JP/ACS?
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Alpha-Omega

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Re: Chemical Identification of an unknown alkali
« Reply #70 on: January 10, 2008, 04:49:51 PM »

USP = United States Pharmacopia
EP = European Pharmacopia
JP = Japanese Pharmacopia
ACS = American Chemical Society
BP = British Pharmacopia

These books contain methods which are GLOBALLY accepted in the Pharmaceutical industry and the methods are also used in other industries.

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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #72 on: January 11, 2008, 07:02:37 PM »

Found some standard methods for flame test, titrimetric analysis in JP.  None in others.  Thanks for sharing these useful websites to me.
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Alpha-Omega

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Re: Chemical Identification of an unknown alkali
« Reply #73 on: January 11, 2008, 07:21:41 PM »

You are welcome!!!!
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #74 on: January 11, 2008, 10:48:52 PM »

Borek, could you please tell me the source of reference for the statement: titrimetric analysis for pKa is suitable for pH3-11? 
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