Consider a saturated solution of zinc arsenate, Zn3(AsO4)2, in which the followi
ID: 903162 • Letter: C
Question
Consider a saturated solution of zinc arsenate, Zn3(AsO4)2, in which the following can occur:
Zn3(AsO4)2 (s) <----> 3 Zn^2+ + 2 AsO4^3- Ksp= 1.0 x 10^-27
AsO4^3- + H20 <-----> HAsO4^2- + OH- Kb1= 3.1 x10^-3
HAsO4^2- + H20 <----> H2AsO4^- + OH- Kb2= 9.1 x10^-8
HAsO4^2- + H20<-----> H3AsO4 + OH- Kb3= 1.7 x10^-12
a) Write mass and charge balance for this solution
b) Find the concentration of Zn^2+ in the solution if the pH is fixed at 6.00.
Explanation / Answer
A)
from this equation we found that AsO4 can abstract 3 hydrogen and release 3 OH- ions from water
charge of AsO4 will be 3- and Zn can abstract 2 OH
3 Zn(OH)2 + 2 H3AsO4 --> Zn3(AsO4)2 + 6 H2O
B) pH = - log (H+) = 6
[H+] = 106