Question

Ethylenediamine (shown below) is a chelate that is typically abbreviated as "end" The formation constants, K_F, of octahedral Ni^2+ complex ions at 25 degree C are: Write the reactions for the formation and the formation constants (in terms of concentrations) for each complex ion The Delta H_f of the two complex ions are the same to two significant figures How do you explain the difference in formation constants? If NH_3 were added to an aqueous solution of [Ni(en)_3]^2+ such that both concentrations were initially 1 M after mixing, what would happen'? Write the reaction and discuss on which side the equilibrium would lie. and why If ethylenediamine were added to an aqueous solution of [Ni(NH_3)_6]^2+ such that both concentrations were initially 1 M alter mixing, what would happen? Again, write the reaction and discuss on which side the equilibrium would lie, and why

Answer 1

For the given complexes

a) Ni2+ + 3en <==> [Ni(en)3]2+     Kf = [Ni(en)3]2+/[Ni2+][en]^3

Ni2+ + 6NH3 <==> [Ni(NH3)6]2+]   Kf = [Ni(NH3)6]2+]/[Ni2+][NH3]^6

b) The formaion of [Ni(en)3]2+ is more fassile due to less steric crowding around central atom and thus has higher formstion constant.

c) NH3 addition would casue the equilibrium reaction to shift towards the right handside, that is formation of more products would occur. this is according to the Lechatelier's principle.

d) complex + en would form more complex and any left Ni2

= would react with added en and form more complex.