The nickel(II) ion in aqueous solution forms complexes with 1,2-
diaminoethane(ethylenediamine) whose ligand replaces two water molecules in the hydrated
complex, i.e. acts as a chelate.
Ni(H2O)2%
6
% enwxxv K1 Ni(H2O4)en 2% % 2H2O
Ni(H2O)4en 2% % en wKxxv2 Ni(H2O)2en 2%
2
% 2H2O
Ni(H2O)2en 2% % en wKxxv3 Nien 2%
3
% 2H2O
The relative values of k1, k2 and k3 will determine the relative proportions of the complexes.
If k3 >>> k2 >>> k1, then addition of ligand will result in formation of Nien3
2+. If k3 <<< k2 <<<
k1, then all four complexes (or three, depending on the absolute magnitude of the constant) will
co-exist in appreciable quantities at equilibrium. The application of Job's Method is limited
to situations where one stage predominates.
In the method, the total molar concentration of nickel(II) plus ligand is kept constant and
the ratio varied from zero to infinity. Initially in a solution containing no nickel(II) ion (ratio
= 0), no complex will be present and the absorbance of the solution is due solely to
diaminoethane. As the concentration of nickel(II) is increased, absorbance will increase (due
to formation of complex) until the molar ratio of nickel(II) to ligand equals the ratio in the
complex. Under the Job conditions, i.e. total molar concentrations of the two species is
constant, this represents the maximum possible concentration of complex. Further increases
in nickel(II) concentration (with corresponding decreases in ligand concentration) will cause
การแปล กรุณารอสักครู่..
