Determination of Manganese in Ferro Manganese, Silico Manganese Using by FAS & back titration with KMnO4

Introduction :

For the determination of Manganese in Ferromanganese & Silico manganese the Sodium Bismuthate , Volhards Methods and Potentiometric Titration Methods have been used in regularly. Here sodium  Bismuthate being rather expensive & time taking, Volhards methods is not accurate & Potentiometric methods needs certain infrastructure. Taken by all three notes we are doing Manganese oxidation by Ammonium Persulfate and reduction with the excesses of Ferrous Sulfate and then back titration with Potassium Permanganate. As the results , necessary conditions for the determination of Manganese needs to investigates more. The procedures of the present method were much more simple compare to Bismuthate & More accurate than Volhards methods.

Reaction :

Fe2+    + MnO4-1           →         Fe 3+  + Mn2+

10FeSO4 +2 KMnO4 + 8H2SO4     →   5Fe2(SO4)3  + K2SO4 + 2MnSO4 + 4H2O

Reagents & Chemicals  :

A)  0.1N ferrous ammonium sulfate solution : (Prepared from ferrous ammonium sulfate crystals and the normality was determined  by  titration  with standard 0.1 N potassium permanganate solution).

B)  Standard 0.1 N potassium permanganate solution : (Prepared by  the usual method from potassium permanganate crystals and standardized with sodium oxalate).

C )  Nitric Acid (sp. gr. 1.4)

D)  Sulphuric Acid ( gr. 1.84)

E)  Phosphoric acid  (sp.    1.7)

F)  2% Silver nitrate  solution

G)  Ammonium persulfate around 99% pure GR grade.

Analytical procedures :

Analytical procedures In a 500 ml beaker, 1.0 g of the sample is weighed, about 30 ml of  Hydrochloric acid & 10 ml  Nitric acid (sp. gr. 1.4) is added and the mixture is heated to effect decomposition.10 ml of  Sulfuric acid solution (1 : l) is added, and the  solution  is  evaporated until white fumes begin  to generate, cooled, with water and warmed to dissolve the salts. After cooling, this solution is transferred.

Filter the whole solution in 250ml Volumetric Flask using by Whatman-40 filter paper, remove Silica by hydro fluorination processes and mixed the residual part in main solution and volume made up to the mark.

Take 50 ml of this solution in 500ml beaker and add 40 ml  of  sulfuric  acid  solution  (1 : 1),  5 ml  of  2%   silver  nitrate  solution  and  10 ml  of   phosphoric  acid  (  are  added and the   diluted   to  the   mark   with   water till 250ml.This  mixture  is  boiled  with  about 5g of ammonium persulfate until small bubbles change to large  bubbles,  then  boiled further for 2 minutes until a large bubble comes up intermittently. After complete decomposition of ammonium persulfate  by this boiling,  the  solution is cooled, about  10 ml of excess  0.1N  ferrous ammonium  sulfate  solution  is added,  and  the  mixture is back titrated with 0.1N potassium permanganate solution. A blank analysis also run along with the sample. The quantity of manganese is calculated from the following equation :

% Mn (by mass) =  (V1-V2)x N x 0.1099 x 100


V1= Volume in ml, of Potassium permanganate required for ferrous ammonium sulphate used .

V2=Volume in ml, of Potassium permanganate required for the back titration.

N =Normality of Potassium permanganate.

M =mass in g , of the sample taken.

Analytical results :

Results obtained by the analysis of various samples by the above procedures are

Sl No Commodity Declared of CRM value (Mn) Obtained value of CRM (Mn)
01 Ferro Manganese
(ECRM 502-2)
77.87%  77.67%  & 77.96%
02 Ferro Manganese

JSS -701-5

 74.14%  73.89% &  74.32%
03 Silico Manganese

NCS HC 28616

62.53% 62.58%  & 62.72%


  1. Digestion & dissolution might be little bit difference in the case of Ferromanganese but Silicomanganese similar processes follows.
  2. Determination of manganese by oxidation with ammonium persulfate and reduction with the excess of ferrous sulfate and then back titration with potassium permanganate was examined from various angles and the following results were obtained.

Contributed by: Sukhenjit Datta  & Sourav Bharati  under the guidance of Prof. B.K. Gupta .