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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Chaste on October 27, 2010, 10:43:11 AM

Title: How to obtain concentration of a FeG+ using activity coefficient?
Post by: Chaste on October 27, 2010, 10:43:11 AM

Equilibria involved :
FeG⁺ + G^-  ::equil:: FeG₂ K₂ = 3.2 x 10³
G^- + H₂O  ::equil:: HG + OH^- K_b = 6.0 x 10^-5
G_- is the amino acid glycine.
Suppose that 0.050 mole of FeG₂ is dissolved in 1 litre of water.

Qns: Using activity coefficient, find FeG⁺ if the pH is fixed at 8.5 and the ionic strength is 0.10M. For FeG⁺, use gamma = 0.79. and for G_- use gamma = 0.782

My attempt at the question:

MBE 1 = 0.05 = [FeG⁺] + [FeG₂]
MBE 2 = [FeG⁺] = [HG] + [G^-]

the ionic strength being 0.1,

0.1 = 0.5 x [FeG⁺] + [G^-] + [H₃O⁺] + [OH_-]   ----- 1

and I'm stuck. I suppose I need to solve simultaneous equations. how do I make use of the pH and activity coefficients to resolve this question?

Title: Re: How to obtain concentration of a FeG+ using activity coefficient?
Post by: Pradeep on December 16, 2010, 01:03:30 PM

Can use debye-hukal law to relate the concentration and ionic strength.

Title: Re: How to obtain concentration of a FeG+ using activity coefficient?
Post by: Chaste on December 16, 2010, 09:23:26 PM

hi there, thanks for the contribution. The question has been there for a while and it has been solved.