![SHREE MALLIKARJUN COLLEGE CLASS:SYBSC
SAFETY: Refer to MSDS of Ethylenediaminetetraacetic acid disodium salt, cobalt chloride, ammonium hydroxide,
ammoniumchloride, xylenol orange, Eriochrome Black-T, zinc sulphate. -Dr. Mithil S. Fal Desai
Aim: Estimate volumetrically the amount of cobalt in CoCl2. H2O by EDTA method using
hexamine.
Chemicals: Ethylenediaminetetraacetic acid disodium salt (EDTA), cobalt chloride, ammonium
hydroxide, ammonium chloride, xylenol orange, Eriochrome Black-T (EBT), zinc sulphate.
Apparatus: Standard volumetric flask, pipette, burette, conical flask, beakers, funnel and glass
rod.
Theory: In the complexometric titration of Co2+ and EDTA, xylenol orange [N,N-
di(carboxymethyl)aminomethyl-o-cresolsulphonphthalein] is used as an indicator. The titration is
carried out in the presence of hexamine at pH 6. The metal-indicator complex is red, while in
hexamine (pH 6) the color of the indicator is yellow. The exact concentration of EDTA salt
solution is determined using zinc sulphate heptahydrate at pH 10 using EBT indicator.
Co2+ + Na2C10H14N2O8 [CoC10H12N2O8]2- + 2Na+ + 2H+
Zn2+ + Na2C10H14N2O8 [ZnC10H12N2O8]2- + 2Na+ + 2H+
Procedure:
A) Preparation of 0.01M EDTA (100 mL) calculate
B) Preparation of 0.01M ZnSO4.H2O (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 (~0.01M)
Rinse and fill the burette with EDTA salt solution. Pipette out 10 mL of 0.01M 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 Co2+ ions.
Pipette out 10 mL of Co2+ ion solution in a conical flask. Add about 1 g of hexamine to adjust the
pH and add 2-3 drops of xylenol orange indicator. Titrate with EDTA until the red color of the
solution changes to yellow. Repeat the titration to get constant readings.
Results: i) Strength of EDTA solution =____M
ii) Strength of given Co2+ ion solution =____M
iii) Amount of Co2+ in given sample = ____g/L.
iv) Amount of CoCl2.H2O in given sample = ____g/L.
Further reading
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.
2) Analytical Chemistry: An Introduction, D. A. Skoog, D. M. West, F. J. Holler, S. R. Crouch,
7th ed](https://image.slidesharecdn.com/estimatevolumetricallytheamountofcobaltincocl2-210419053952/85/estimate-volumetrically-the-amount-of-cobalt-in-co-cl2-h2o-by-edta-method-using-1-320.jpg)
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Estimate volumetrically the amount of cobalt in co cl2. h2o by edta method using
- 1. SHREE MALLIKARJUN COLLEGE CLASS:SYBSC SAFETY: Refer to MSDS of Ethylenediaminetetraacetic acid disodium salt, cobalt chloride, ammonium hydroxide, ammoniumchloride, xylenol orange, Eriochrome Black-T, zinc sulphate. -Dr. Mithil S. Fal Desai Aim: Estimate volumetrically the amount of cobalt in CoCl2. H2O by EDTA method using hexamine. Chemicals: Ethylenediaminetetraacetic acid disodium salt (EDTA), cobalt chloride, ammonium hydroxide, ammonium chloride, xylenol orange, Eriochrome Black-T (EBT), zinc sulphate. Apparatus: Standard volumetric flask, pipette, burette, conical flask, beakers, funnel and glass rod. Theory: In the complexometric titration of Co2+ and EDTA, xylenol orange [N,N- di(carboxymethyl)aminomethyl-o-cresolsulphonphthalein] is used as an indicator. The titration is carried out in the presence of hexamine at pH 6. The metal-indicator complex is red, while in hexamine (pH 6) the color of the indicator is yellow. The exact concentration of EDTA salt solution is determined using zinc sulphate heptahydrate at pH 10 using EBT indicator. Co2+ + Na2C10H14N2O8 [CoC10H12N2O8]2- + 2Na+ + 2H+ Zn2+ + Na2C10H14N2O8 [ZnC10H12N2O8]2- + 2Na+ + 2H+ Procedure: A) Preparation of 0.01M EDTA (100 mL) calculate B) Preparation of 0.01M ZnSO4.H2O (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 (~0.01M) Rinse and fill the burette with EDTA salt solution. Pipette out 10 mL of 0.01M 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 Co2+ ions. Pipette out 10 mL of Co2+ ion solution in a conical flask. Add about 1 g of hexamine to adjust the pH and add 2-3 drops of xylenol orange indicator. Titrate with EDTA until the red color of the solution changes to yellow. Repeat the titration to get constant readings. Results: i) Strength of EDTA solution =____M ii) Strength of given Co2+ ion solution =____M iii) Amount of Co2+ in given sample = ____g/L. iv) Amount of CoCl2.H2O in given sample = ____g/L. Further reading 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. 2) Analytical Chemistry: An Introduction, D. A. Skoog, D. M. West, F. J. Holler, S. R. Crouch, 7th ed