Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryCoordination Compounds4 Marks
Question
Name the factors governing the equilibrium constants of the coordination compounds.
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Answer
The equilibrium constant of the complex depends on the following factors:
(a) Charge to size ratio of the metal ion: Higher the ratio greater is the stability. For the divalent metal ion complexes their stability shows the trend: $Cu ^{2+}$ > $Ni ^{2+}> Co ^{2+}> Fe ^{2+}> Mn ^{2+}> Cd ^{2+}$. The above stability order is called the Irving-William order. In the above list both Cu and Cd have the charge $+2$ , however, the ionic radius of $Cu 2+$ is $69\ pm$ and that of $Cd 2+$ is $97\ pm$ . The charge to size ratio of $Cu ^{2+}$ is greater than that of $Cd ^{2+}$. Therefore the $Cu ^{2+}$ forms stable complexes than $Cd ^{2+}$.
(b) Nature of the ligand: A second factor that governs stability of the complexes is related to how easily the ligand can donate its lone pair of electrons to the central metal ion that is, the basicity of the ligand. The ligands those are stronger bases tend to form more stable complexes.
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