ADITYA ENVIRONMENTAL SERVICES PVT LTD S.O.P. for :Determination of organic carbon and organic matter in Soil Document No. : AESPL/LAB/S/P/07 Revision No. : 00 Revision Date : 01/08/2012 Page No. : 1 of 1 Clause Ref. : 5.4 Scope: To determine the Organic Carbon and Organic Responsibility : Chemist Reference: Manual of Soil testing in India(Department of Agriculture &co-operation, Ministry of agriculture (Government of India),IS:2720 (Part XXII)-1972 Principle: Organic Carbon is determined by titrating the solid sample with known amount of Potassium dichromate in the presence of concentrated sulphuric acid, Oxidation of organic carbon by potassium dichromate Volumetric method.(Walkley and Black,1934) 2K2Cr2O7 + 8H2SO4 →2K2SO4 +2Cr2(SO4)3 + 8H2O+6(O) 3C(Organic carbon)+6H2O→3CO2 The excess chromic acid left unutilized by the organic matter is back titrated with FAS by using diphenylamine indicator Apparatus : • Measuring Cylinder : 50 7250ml • Analytical Balance : • Pipette -10ml • Conical Flask 500ml Reagent : a)Potassium Dichromate (1.0N):Dissolve 49.04gm of dried Potassium Dichromate AR grade in 1000ml distilled water b)Sulphuric acid(Conc)Sp.Gr.1.84 c)Diphenylamine indicator :Dissolve 0.5g of Diphenylamine in a mixture of 100ml concH2SO4 and 20 ml distilled water d)Ferrous ammonium sulphate(1.0N):Dissolve 392.2g of FAS in 1000ml of distilled water containing 20ml Sulphuric acid e)Sodium Fluoride f)O-Phosphoric Acid(85%): Mix 85ml of ortho-phosphoric acid(100%) and 15ml of distilled water PREPARED BY : CHECKED BY : STAMP :
Scope: To determine the Organic Carbon and Organic
Responsibility : Chemist
Reference: Manual of Soil testing in India(Department of
Agriculture &co-operation, Ministry of agriculture (Government
of India),IS:2720 (Part XXII)-1972
Principle: Organic Carbon is determined by titrating the solid
sample with known amount of Potassium dichromate in the presence of
concentrated sulphuric acid, Oxidation of organic carbon by
potassium dichromate Volumetric method.(Walkley and Black,1934)
2K2Cr2O7 + 8H2SO4 2K2SO4 +2Cr2(SO4)3 + 8H2O+6(O) 3C(Organic
carbon)+6H2O3CO2 The excess chromic acid left unutilized by the
organic matter is back titrated with FAS by using diphenylamine
indicator
Reagent : a)Potassium Dichromate (1.0N):Dissolve 49.04gm of
dried Potassium Dichromate AR grade in 1000ml distilled water
b)Sulphuric acid(Conc)Sp.Gr.1.84 c)Diphenylamine indicator
:Dissolve 0.5g of Diphenylamine in a mixture of 100ml concH2SO4 and
20 ml distilled water d)Ferrous ammonium sulphate(1.0N):Dissolve
392.2g of FAS in 1000ml of distilled water containing 20ml
Sulphuric acid e)Sodium Fluoride f)O-Phosphoric Acid(85%): Mix 85ml
of ortho-phosphoric acid(100%) and 15ml of distilled water
PREPARED BY :
CHECKED BY :
STAMP :
ADITYA ENVIRONMENTAL SERVICES PVT LTD
S.O.P. for :Determination of organic carbon and organic matter
in Soil
Procedure : Take 0.25g of oven dried sample thoroughly grind
through 0.2mm sieve. Transfer this to 500ml conical flask and add
10ml 1N K2CR2O7 solution To it add 20mlConc.H2SO4 and mix gently by
rotation to ensure complete contact.
Allow the mixture to stand for 30minutes Add 200ml distilled
water,10ml phosphoric acid and 0.2 g of sodium fluoride and 1ml
of diphenyl amine indicator Titrate the solution with 1N FAS
solution. The color is dull green at the beginning and
then shift to turbid blue as the titration proceeds .At the end
point the color sharply turns to brilliant green.
Keep the blank titration without sample and follow the same
procedure.
Calculation :
1) Organic Carbon % = { 10-{10S/B}x 0.333 x 100 0.77 wt Where,
S= ml of FAS used for sample titration B = ml of FAS for blank
titration Wt=Weight of the soil sample taken in gm. 0.77=It is
recovery factor i.e. recovery of 77% of organic matter is
considered
Note : One ml of 1N Potassium dichromate is equivalent to 3mg of
of Carbon
2) % Organic Matter =%C x 1.724 The factor 1.724 is based on the
assumption that Carbon is only 58% Organic matter
