Estimation of manganese in presence of iron

1. SHREE MALLIKARJUN COLLEGE CLASS:TYBSC
SAFETY: Refer to MSDS of ethylenediaminetetraacetic acid disodium salt (EDTA), ferromanganese alloy, ammonium
hydroxide, ammonium chloride, hydroxylammonium chloride, thymolphthalexone, hydrochloric acid, nitric acid,
triethanolamine, Eriochrome Black-T (EBT), zinc sulphate. -Dr. Mithil S. Fal Desai
Aim: Estimation of manganese in presence of iron in ferromanganese by EDTA titration.
Chemicals: Ethylenediaminetetraacetic acid disodium salt (EDTA), ferromanganese alloy,
ammonium hydroxide, ammonium chloride, hydroxylammonium chloride, thymolphthalexone,
hydrochloric acid, nitric acid, triethanolamine, Eriochrome Black-T (EBT), zinc sulfate.
Apparatus: Volumetric flask, pipette, burette, conical flask, beakers, funnel and glass rod.
Theory: Ferromanganese is an alloy of Mn (76-80%), Fe (12-15%), and C (up to 7.5%) which is
used as a deoxidizer for steel. The dissolution of this alloy is done by a mixture of concentrated
nitric acid and hydrochloric acid. As Fe being a metal that interferes with EDTA titration, Fe is
masked with triethanolamine (CH2OHCH2)3N in a basic medium. The manganese is then titrated
with a standardized EDTA solution using a thymolphthalexone indicator. The blue to colorless (or
light pink) change is observed at the endpoint. The Mn can be also titrated with EDTA using
Eriochrome Black-T in basic buffer (pH-10) when Fe is not present in the solution to interfere.
The exact concentration of EDTA salt solution is determined by titrating it with a standard solution
of Zn2+ at pH 10, using an EBT indicator.
(CH2OHCH2)3N + Fe3+  Fe(OCH2CH2)3N +H+
Mn2+ + Na2C10H14N2O8  [MnC10H12N2O8]2- + 2Na+ + 2H+
Zn2+ + Na2C10H14N2O8  [ZnC10H12N2O8]2- + 2Na+ + 2H+
Procedure:
A) Preparation of 0.05M EDTA (100 mL) calculate
B) Preparation of 0.05M ZnSO4.7H2O (100 mL) calculate
C) Preparation of buffer of pH 10
Dissolve 32 g of NH4Cl in 300 mL of 28-30% ammonia solution. Slowly and carefully add 200
mL distilled water.
D) Standardization of EDTA salt solution (~0.05M)
Rinse and fill the burette with EDTA salt solution. Pipette out 10 mL of 0.05M of ZnSO4 solution
and add 10 mL of a buffer of pH 10. Add 2-3 drops of EBT indicator solution to the flask. Titrate
the solution from the flask against EDTA until the wine red color of the solution changes to blue.
Repeat the titration to get constant readings.
E) Estimation of manganese
Dissolve 0.4 g of ferromanganese alloy in 1.5 mL of nitric acid and 2.0 mL of hydrochloric acid.
Boil the content if necessary. Cool the mixture and filter it through coarse filter paper. Transfer
the content quantitatively and dilute it upto the mark in a 100 mL standard flask. Pipette out 10
mL of the diluted solution in a clean conical flask and add 2.5 mL 10% aqueous
hydroxylammonium chloride. Add 5 mL of 20% aqueous triethanolamine solution, 5-20 mL
concentrated ammonia solution (until pH is ~10), 50 mL double distilled water and 3-4 drops of
thymolphthalexone indicator. Titrate this solution against standardized 0.05 M EDTA until the
color change is observed from blue to colorless. Repeat the titration to get constant readings.

2. SHREE MALLIKARJUN COLLEGE CLASS:TYBSC
SAFETY: Refer to MSDS of ethylenediaminetetraacetic acid disodium salt (EDTA), ferromanganese alloy, ammonium
hydroxide, ammonium chloride, hydroxylammonium chloride, thymolphthalexone, hydrochloric acid, nitric acid,
triethanolamine, Eriochrome Black-T (EBT), zinc sulphate. -Dr. Mithil S. Fal Desai
Results: i) Strength of EDTA solution =____M
ii) Strength of given Mn2+ ion solution =____M
iii) Amount of Mn in given ferromagnese alloy = ____g.
iv) Percentage of Mn in ferromanganese alloy = ____%.
1) Vogel’s textbook of quantitative chemical analysis, J. Mendham, R. C. Denney, J. D. Barns, M.
Thomas, B. Sivasankar, Pearson India Education, 6th Edition.