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Topic: Chemical Oxygen Demand  (Read 4343 times)

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Offline gamal

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Chemical Oxygen Demand
« on: September 27, 2007, 05:10:13 PM »
In the C.O.D. Test using KMnO4 and 3:1 H2SO4 we digest the mixture for 30 min in water bath,

the qustion is wt really happen in this period and what is the oxidation state of the Manganous oxide present in the mixture  :-\after this period ??


Offline carnation

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Re: Chemical Oxygen Demand
« Reply #1 on: October 08, 2007, 10:48:45 PM »
As I know, when you determine COD by using KMnO4 in H2SO4, the organic matter will be oxidized and form CO2 and other inorganic components. Mn in KMnO4 (+7) is reduced to Mn(+2), below is the simple equation for this :
Organic matter + KMnO4 + H2SO4  ==MnSO4 + K2SO4 + CO2 + H2O
But in recent days, people have not used this method more often because KMnO4 just oxidize about 75% organic matter. In stead of using KMnO4, we can use K2Cr2O7.(can oxidize about 90% organic matter)
Good luck

Offline tripton

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Re: Chemical Oxygen Demand
« Reply #2 on: October 10, 2007, 10:03:59 AM »
I donĀ“t know exactly the final oxidation state of Mn, but I agree that the usual method uses dichromate. If you just want to get a good COD result, you may follow any standardized method but if you must know exactly what happen with the Mn, perhaps you must look for some paper of try to do your own research making Mn speciation analysis in the final solutions.

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