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 (sp.gr.1.7) 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
M
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% |
Summary:
- Digestion & dissolution might be little bit difference in the case of Ferromanganese but Silicomanganese similar processes follows.
- 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 .