What do you understand by the term stability constant, K of a complex? Knowing that the value of K for [Cu(NH₃)₄]²⁺ is 4.5 x 10¹¹ and for [Cu(CN)₄]^2– is 2.0 x 10²⁷, suggest
(a) Which complex species will furnish less Cu²⁺ ions in solution and
(b) Which out of NH₃and CN^– is a stronger ligand?

Stability constant (K) of a complex. The formation of a complex in solution is a reversible reaction.

where a = charge on the metal ion, x = charge on the ligand and b⁺ = charge on the complex ion.

(a^{+}) + n (x) = (b^{+})

Stability constant,

(K) = \frac{(MLn)^{b +}}{[M^{a +}] {[L^{x}]}^{n}}

(a)

K for {[Cu ({NH}_{3})_{4}]}^{2 -}

= \frac{{[Cu ({NH}_{3})_{4}]}^{2 +}}{[{Cu}^{2 +} (aq)] [{NH}_{3} (aq)]^{4}} = 4.5 \times 10^{11} . . . (i)

= \frac{[Cu ({NH}_{3})_{4}]^{2 +}}{[{Cu}^{2 +} (aq)] [{NH}_{3} (aq)]^{4}} = 4.5 \times 10^{11} . . . (i)

K for {[Cu (CN)_{4}]}^{2 -} = \frac{{[Cu (CN)_{4}]}^{2 -}}{[{Cu}^{2 +} (aq)] [{CN}^{-} (aq)]^{4}} = 2.0 \times 10^{27} . . . (ii)

Evidently, concentration of CN^–(aq) ions furnished by [Cu(CN)₄]^2– complex ion is less than that furnished by [Cu(NH₃)₄]²⁺ complex ion.

(b) Since CN^– ligand forms more stable complex with Cu²⁺ ions than NH₃ ligand with Cu²⁺ ions, so CN^– ligand is a stronger ligand than NH₃.

188 Views

Coordination Compounds

Hope you found this question and answer to be good. Find many more questions on Coordination Compounds with answers for your assignments and practice.

Chemistry I

Browse through more topics from Chemistry I for questions and snapshot.

What do you understand by the term stability constant, K of a complex? Knowing that the value of K for [Cu(NH3)4]2+ is 4.5 x 1011 and for [Cu(CN)4]2– is 2.0 x 1027, suggest(a) Which complex species will furnish less Cu2+ ions in solution and (b) Which out of NH3and CN– is a stronger ligand?

Coordination Compounds

Chemistry I