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Author Topic: Comercial Caustic Soda analysis  (Read 11409 times)

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quimisel

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Comercial Caustic Soda analysis
« on: May 08, 2006, 05:12:32 AM »

Hi.. i need some help here..
can anyone tell me where i can find some information about this... what i need exactly is something about warder and winkle methods...i googled but cannot find anything about it...
please replay me if you know anything about it...
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eugenedakin

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Re: Comercial Caustic Soda analysis
« Reply #1 on: May 10, 2006, 06:26:02 PM »

Hello quimisel,

I have performed many variations of industrial sodium hydroxide analysis, but I honestly do not remember a method by that name.  Could you help me out with your question ... what are you attempting to analyze this chemical for?   Is this to meet food grade, or water quality grade specifications?

Thanks for your time,

Eugene
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There are 10 kinds of people in this world: Those who understand binary, and those that do not.

AWK

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Re: Comercial Caustic Soda analysis
« Reply #2 on: May 10, 2006, 07:51:53 PM »

What do you want to analyse - NaOH content, Na2CO3 content or others?
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Alberto_Kravina

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Re: Comercial Caustic Soda analysis
« Reply #3 on: May 11, 2006, 01:07:40 AM »

What do you want to analyse - NaOH content, Na2CO3 content or others?
I presume that if quimisel wants to know about WARDER and WINKLER method (s)he wants to analyze the content of NaOH and Na2CO3
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AWK

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Re: Comercial Caustic Soda analysis
« Reply #4 on: May 11, 2006, 01:41:41 AM »

This is an excerpt from:
http://etd.gatech.edu/theses/available/ipstetd-139/fary_ad.pdf

With the so-called Winkler method (25) the total alkali of a sample was
determined by titration with approximately 0.50N standard HC1 to a mixed indicator
(bromocresol green-methyl red) end point. The free hydroxide was then
determined on a duplicate sample by precipitation of the carbonate with excess
barium chloride and titration to a phenolphthalein end point with the standard
acid. By subtracting the free hydroxide value from the total alkali, the amount
of carbonate was obtained.
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Alberto_Kravina

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Re: Comercial Caustic Soda analysis
« Reply #5 on: May 11, 2006, 02:06:04 AM »

Brief explanation of the so-called Warder method:

By adding HCl to a sodium hydroxide-sodium carbonate mixture you completely neutralize the NaOH molecules:
NaOH + HCl ? NaCl + H2O
The carbonate ions don't react to CO2, but they are protoned to Hydrogen carbonate.
Na2CO3 + HCl ? NaCl + NaHCO3

End point of this reactions is determined with Phenolphtaleine (color turns from pink to colorless).
=>Volume of HCl needed until color turn of Phenolphtaleine = VA

Afterwards you add methyl orange and titrate until the solution turns from red to orange.
In this last step the hydrogen carbonate anions are completely protonated to carbonic acid:
NaHCO3 + HCl ? NaCl + H2O + CO2
=>Volume of HCl used until Methyl orange color turns = Vb


=>V(HCl)to neutralize NaOH=VA-VB
=>V(HCl)to neutralize Na2CO3= 2*VB

Both Warder and Winkler methods are pretty accurate, I analyzed a conc. Soda lye solution some time ago and both results were very good: http://www.chemicalforums.com/index.php?topic=7556.0
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quimisel

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Re: Comercial Caustic Soda analysis
« Reply #6 on: May 11, 2006, 08:49:03 AM »

hey...thanks for your replays...
in my experiment i had to analyse the % of Na2CO3 and NaOH on a Commercial Caustic Soda and have to right a report about that....but i dont know what to write in "Introduction", im so confused...hope you can help me :D

Thanks
Quimisel
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Alberto_Kravina

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Re: Comercial Caustic Soda analysis
« Reply #7 on: May 12, 2006, 01:51:17 AM »

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quimisel

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Re: Comercial Caustic Soda analysis
« Reply #8 on: May 12, 2006, 03:28:24 AM »

thanks...this will help me:D
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quimico1

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Re: Comercial Caustic Soda analysis
« Reply #9 on: June 24, 2006, 05:49:57 PM »

Hi.. i need some help here..
can anyone tell me other method for Analysis of carbonate content in sodium hydroxide solution diferent of warder and winkler methods...i googled but cannot find anything about it...
please replay me if you know anything about it...
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quimico1

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Re: Comercial Caustic Soda analysis
« Reply #10 on: June 24, 2006, 05:55:49 PM »

Hi.. i need some help here..
can anyone tell me other method for Analysis of carbonate content in sodium hydroxide solution diferent of warder and winkler methods...i googled but cannot find anything about it...
please replay me if you know anything about it...
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Alberto_Kravina

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Re: Comercial Caustic Soda analysis
« Reply #11 on: June 24, 2006, 10:43:40 PM »

Quote
can anyone tell me other method for Analysis of carbonate content in sodium hydroxide solution diferent of warder and winkler methods...i googled but cannot find anything about it...
Mmmmm, as far as I know these are the best methods to determine carbonate in NaOH.
One possible method could be to add acid and measure the amount of CO2. Or you could pass the CO2 in Barium hydroxide, filter the precipitated Barium carbonate, dissolve it in excess HCl and back titrate the excess of HCl with NaOH, however, I doubt that these methods would be accurate.

Why do you need a different method, just out of curiosity ???
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quimico1

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Re: Comercial Caustic Soda analysis
« Reply #12 on: June 25, 2006, 08:49:47 AM »

For the determination of sodium carbonate in commercial caustic soda, there is no satisfactory direct volumetric method, and usually a determination of carbon dioxide is resorted to. Winkler’s method yields higher results, owing to the precipitation of barium silicate, and to the precipitation of basic barium carbonate, when carried out according to the usual procedure.
Theoretically Warder’s method is suitable for mixtures containing much hydroxide and little carbonate, like commercial caustic soda, but the usual procedure is far from precise. Slight errors in the two end points affect the result seriously. If 45 cc. of a standard acid are used for the complete titration and an error of 0.04 cc. is made at each end point, the result for carbonate would be affected by 0.36 per cent when the errors are cumulative in nature.
Impurities that might occur in appreciable quantities in commercial caustic soda are sodium silicate, sodium aluminate,
iron, lime, and magnesia. Sodium silicate behaves like sodium hydroxide during the titration and offers no interference in the carbonate determination. Sodium aluminate is decomposed with the separation of aluminum hydroxide at the first end point. Aluminum hydroxide as well as ferric hydroxide, lime, and magnesia consume part of the acid for the second end point and, when present in appreciable quantities, cause a positive error in the carbonate determination.
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