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Author Topic: Chemical Identification of an unknown alkali  (Read 57877 times)

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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #75 on: January 14, 2008, 09:21:25 PM »

No reply yet.  But I wonder what the people in the old days use when they did not have the sophisticated instruments such as IC, etc.  Did they not do any prelim. id?
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AWK

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Re: Chemical Identification of an unknown alkali
« Reply #76 on: January 14, 2008, 10:00:27 PM »

No reply yet.  But I wonder what the people in the old days use when they did not have the sophisticated instruments such as IC, etc.  Did they not do any prelim. id?
these preliminary tests are called qualitative analysis and eventually chemical-technical analysis if samples are not pure. Did you read any texbook on this subjest.
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #77 on: January 14, 2008, 10:33:05 PM »

I did read some textbooks.  Qualitative analysis is for id of cations and anions.  Seems not comprehensive enough for acids and some bases.  But I haven't seen a term chemical-technical analysis. Could you suggest any references pls?
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #78 on: January 15, 2008, 12:48:20 AM »

I found a  really old book, dated 1898, An introduction to Chemical Technical analysis.
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AWK

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Re: Chemical Identification of an unknown alkali
« Reply #79 on: January 15, 2008, 01:36:09 AM »

I did read some textbooks.  Qualitative analysis is for id of cations and anions.  Seems not comprehensive enough for acids and some bases.  But I haven't seen a term chemical-technical analysis. Could you suggest any references pls?
Acids contains anions, bases contains cations you can find in your samples. Qualitative analysis works this way over 150 years and is sufficient to identify also acids and bases. Simply if you cannot find any cation, and solution is sufficiently acidic, then you have the acid containing this anion. Of course this is valid for individual substances.
In the case of mixtures, inorganic qualitative analysis detects only cations and anions (also a few organic anions).
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #80 on: January 15, 2008, 04:27:20 AM »

Do you mean if I find Cl- ion by qualitative analysis and the pH is low (? how low), then I can say it is HCl?  In the same sense, if I find Na in a pH 13 liq that gives NH3 gas when NH4Cl is added, I can say this is NaOH?
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #81 on: January 15, 2008, 04:31:42 AM »

I am intending to use acid base titration for weak acid to decide its pKa and check from a table for the corresponding acid's ID.  This doesn't work for strong acid as Borek stated.  If I can find the cation, how can I say the anion is H+?  Also, I want to use qualitative analysis to test for the cation and anion in a base.  what do you think of this approach?
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #82 on: January 15, 2008, 04:34:06 AM »

sorry, should be "If I can find the anion, how can I say the cation is H+? 
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Borek

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Re: Chemical Identification of an unknown alkali
« Reply #83 on: January 15, 2008, 05:22:29 AM »

I am intending to use acid base titration for weak acid to decide its pKa and check from a table for the corresponding acid's ID.  This doesn't work for strong acid as Borek stated.

I have also stated it will not work for weak acids, as the accuracy of the pKa determination is low and there are too many acids with very similar pKa values. Alpha-Omega told you the same thing.
« Last Edit: January 16, 2012, 08:46:42 AM by Arkcon »
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Borek

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Re: Chemical Identification of an unknown alkali
« Reply #84 on: January 15, 2008, 05:23:11 AM »

If I can find the anion, how can I say the cation is H+? 

If you have eliminated all other possible cations you are left with H+ only.
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #85 on: January 15, 2008, 07:28:36 PM »

My boss doesn't want to invest on IC, etc.  So the only thing I can count on is simple titration for acids like acetic, carbolic, chromic, formic, monochloroacetic, oxalic, phosphoric acids.  For HCl, HF, nitric, sulfuric acid I may use qualitative analysis for anions, and exclusion of other cations for H+.
I'd love to use IC if I had this instrument.  Many constraints when cost  is concerned.
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Borek

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Re: Chemical Identification of an unknown alkali
« Reply #86 on: January 15, 2008, 09:05:51 PM »

Instead of titration you may as well try card reading - much cheaper and similar accuracy.
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #87 on: January 15, 2008, 09:45:23 PM »

What is this please: card reading? 
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Borek

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Re: Chemical Identification of an unknown alkali
« Reply #88 on: January 15, 2008, 10:09:19 PM »

What is this please: card reading?

Fortune telling with deck of cards, like palm reading.

We told you several times that titration will not work as ID method yet you still cling to it.
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Edward

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Re: Chemical Identification of an unknown alkali
« Reply #89 on: January 15, 2008, 10:22:09 PM »

Should I rather tell my boss we can do nothing except buy an IC?
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