Insoluble salts can sometimes be brought into solution by the formation of a sol
ID: 506208 • Letter: I
Question
Insoluble salts can sometimes be brought into solution by the formation of a soluble complex ion. For example, AgCl(s) can be dissolved in ammonia solutions by the formation of the soluble Ag(NH_3)^+_2 complex ion. The ammonia competes with the Cl^- ion for reaction with Ag^+ as follows: AgCl(s) doubleheadarrow Ag^+ (aq) + Cl^- (aq) K_sp = [Ag^+][Cl^-] = 1.8 times 10^-10 Ag^+(aq) + 2NH_3(aq) doubleheadarrow Ag(NH_3)^+_2(aq) K_formation = [Ag(NH_3)^+_2]/[Ag^+][NH_3]^2 = 1.6 times 10^7 Sum: AgCl(s) + 2NH_3 (aq) doubleheadarrow Ag(NH_3)^+_2 (aq) + Cl^- (aq) K_net = K_formation times K_sp = [Ag(NH_3)^+_2] [Cl^-]/[NH_3]^2 = 2.9 times 10^-3 Assuming all the Cl^- comes from the dissociation of AgCl, then [Ag(NH_3)^+_)2 = [NH_3] times Squareroot 2.9 times 10^-3. What is the maximum [Ag(NH_3)^+_2] that can be obtained by dissolving AgCl in 1.5 M ammonia? For another silver salt, AgBrO_3, K_sp = 5.4 times 10^-5. What is K_net for the reaction AgBrO_2 + 2NH_3 doubleheadarrow Ag(NH_3)^+_2 + BrO^-_3? What is the maximum [Ag(NH_3)^+_2] that can be obtained by dissolving AgBrO_3 in 4.1 M ammonia?Explanation / Answer
Q4) From the discussion in the probelm
[Ag(NH3)2+] = [NH3] (2.9x10-3)1/2
Since [NH3] = 1.5 M
the maximum complex ion that can be formed = 1.5M x (2.9x10-3)1/2
= 0.0808 M
Q5) In asimilar manner Knet for
AgBrO3 (s) + 2NH3 <----------> Ag(NH3)2 + BrO3-
Knet = kf x Ksp
= 1.6x107x5.4x10-5
=8.64x102
The maxium [Ag(NH3)2 = [NH3] (8.64x102 )1/2
= 4.1 x(8.64x102 )1/2
=1.205 x102 M