the acid attack in carbonate analysis produce Co2 gaz which may comme from the oxidation of organic matter, so i was wondering if the FeSo4 can eliminate this oxidation and by which mechanism it can do so?
Please be little more specific in stating the problem.
Dr. Mirza Arshad Ali Beg
My concern is whether or not add ferrous sulphate in the HCL solution when i measure Carbonates content in a soil, because HCL car also oxidize Organic matter and this also produce CO2 , so it can overestimating carbonates contents isn't?
HCl isn't an oxidizing acid. The CO2 you get from adding HCl to a sample will come from inorganic carbonate salts/minerals.
Yes, HCl reaction/titration will give you inorganic carbonate and bicabonate and will not oxidize the organic matter. You may have estimate the carbonate and bicarbonate and organic matter by standard procedures, one wof which may involve estimation of soluble carbonate and bicarbonate. The other may require dehydration followed by desiccation and finally incineration from which you will find out the moisture content, the organic matter and the carbonate content.
Mirza Arshad Ali Beg
thank for your answers Doctor Mirza Arshad Ali beg and Doctor Henrik Rasmus Anderson , but i had read in the chapter about carbonates analysis wrote by Allison and Moodie cited in Suarez paper about carbonates and gypsym, that in acid dissolution procedures by Hcl in carbonates analysis , Manganese dioxide can interfere in this procedures and intfluence the oxidation of Organic matter, so they add FeSo4 to the acid in order to minimize oxidation of organic matter!!!
For determination CaCO3 equivalent by classical acid base titration method/calcimeter no FeSo4 is not added.even when soil sample contains gypsum and MnO2.
MnO2 can oxidise organic material in acidic solution. If you add FeSO4 it would make sense that the MnO2 oxidise Fe2+ to Fe3+ preferably to oxidising organic matter.
First: In analysis, the more different substances one adds to a sample, the more reactions become relevant in it, which interfere with the desired reaction and therefore can screw up the outcome of the experiment.
Second: I want to remind you of the old-knewn reaction MnO2 + 2HCl + 2H+ -> Mn2+ + 2H2O + Cl2. Cl2 will lead to chlorination of organic matter, especially if Fe3+ is present.
Third: Which specific organic substances are expeced to release CO2 upon oxidation? Decarboxylation of arene carboxy acids is only relevant at high temperature. Oxidation of formate or oxalate is only relevant in non-acidic medium because these reactions release H+. This is also the reason why ascorbate is preserved from oxidation in acidified conserves, e.g in sauerkraut, which served as a healthy food to inhibit scorbut during long travel on sea (therefore the name ascorbic acid).
Therefore I suggest to do the carbonate analysis without addition of FeSO4.
To go sure, I suggest you to do some comparison experiments: a) add some MnO2 to the sample before acidification. b) add some MnO2 and formiate or oxalate to the sample before acidification. If none of these two conditions lead to significantly increased CO2 yield, then these substances do not interfere with the carbonate analysis.
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