Question

Wanting to form nickel(II) cyanide, Ni(CN)2, a chemist adds hydrocyanic acid, HCN, to a solution containing Ni2+ ions hoping to precipitate Ni(CN)2. The important equlibria for this process are given below:
HCN(aq) <--> H+(aq) + CN-(aq) Ka=4.0x10^(-10)
Ni(CN)2(s) <--> Ni2+(aq) +2CN-(aq) Ksp= 3.0x1-^(-23)

a) what is the equilibrium constant, Knet, for the following reaction which describes the precipitation reaction the chemist wants to perform?
Ni2+(aq) + 2HCN(aq) <--> 2H+(aq) + Ni(CN)2(s)
Knet = ?

b) Can the chemist readily form Nickel (II) Cyanide in this manner?
c) The chemist runs the reaction and allows the solution to come to equilibrium before diluting the solution by a factor of 10. Calculate Q upon dilu
d) Will he get more or less Ni(CN)2 by diluting the solution in this fashion?

Answer 1

(a)

Reverse above reaction
.......(1)

Multiply above equation with 2.
...... (2)

Add equations (1) and (2)

(b) Since the value of the equilibrium constant is much greater than 1, the chemist can readily form Nickel (II) Cyanide in this manner.

(c) Dilution will affect the rate of the reaction but will not affect the value of the equilibrium constant.
The value of Q will be same as the value of K. It will be 5333

(d) He will get same amount of Ni(CN)2 by diluting the solution in this fashion.