Follow the first 5 steps systematic method in the problem below. You do not need
ID: 794599 • Letter: F
Question
Follow the first 5 steps systematic method in the problem below. You do not need to do step 6.
Determine the solubility of HgBr2, a sparingly soluble salt, in the presence of 0.0010 M NH3. NH3 is a weak base that reacts with Hg2+ in the reaction Hg2+ + 4NH3 (aq) ? Hg(NH3)42+. For this problem, you can ignore the effects of ionic strength and also assume that no other metal-ligand complexes form.
The five steps that are wanted are 1) Pertinent reactions, 2) Charge balance, 3) Mass balance, 4) Equilibrium constant expressions, and 5)Count equations and unknowns.
Explanation / Answer
1) HgBr2 --> Hg2+ + 2Br-
Hg2+ + 4NH3 --> [Hg(NH3)4]2+
NH3 + H2O --> OH- + NH4+
2) [NH4+] + [Hg(NH3)42+] + 2[Hg2+] + [H+] --> [Br-] + [OH-]
3) 2[Hg2+] + [Hg(NH3)42+] --> [Br-]
4) Ksp = [Hg2+][NH3]^4
5) 3 equations, 3 unknowns