Question

A solution contains 0.13 M sodium iodide and 0.13 M potassium hydroxide. Solid silver nitrate is added slowly to this mixture. What ionic compound precipitates first from the solution?

Ksp AgI = (1.5e-16)

Ksp AgOH = (2e-8)

Formula of first precipitate = _______

Hint: It is not necessary to do a calculation here.

Answer 1

lets calculate the concentration of Ag+ required for each precipitation

AgI(s)   <—>   Ag+ (aq)   +   I- (aq)

           s           0.13

Ksp = s*(0.13)

1.5*10^-16 = 0.13*s

s = 1.2*10^-15 M

So, when [Ag+] = 1.2*10^-15 M, AgI starts to precipitate

AgOH(s)   <—>   Ag+ (aq)   +   OH- (aq)

           s           0.13

Ksp = s*(0.13)

2*10^-8 = 0.13*s

s = 1.5*10^-7 M

So, when [Ag+] = 1.5*10^-7 M, AgOH starts to precipitate

AgI starts precipitating at lower concentration. So it will be first to precipitate

Answer: AgI