Aqueous solutions of Zn+2 and Pb+2 both .0010M. Both form insoluble sulfides. Appx. what pH will allow maximum precipitation of one ion and leave the other in solution?
Do I just use Ksp and the equations? If so what do I do next?
See the selective solubility notes and example here:
http://pages.towson.edu/ladon/solprod.html
Set up Ksp for Zn(OH)2 and Pb(OH)2.
Calculate (OH^-) for each using 0.001 M for the metal. From this you will see which metal requires the least OH^- and that will tell you the approximatre pH needed. To check yourself, put the (OH^-) back into the Ksp and calculate how much of the metal ion can be in solution.
Post your work if you want us to review it.
To determine the approximate pH that will allow maximum precipitation of one ion and leave the other in solution, you can use the concept of selective solubility and the equilibrium constant for the solubility product (Ksp).
1. Set up the Ksp expressions for the formation of the insoluble sulfides:
- For ZnS: Ksp = [Zn+2][S-2]
- For PbS: Ksp = [Pb+2][S-2]
2. Calculate the concentration of hydroxide ions (OH-) in solution for each metal ion (Zn+2 and Pb+2). Since both solutions have a concentration of 0.0010 M, the concentration of OH- will be the same for both.
3. Use the concentration of OH- to determine which metal ion requires the least OH-. This can be done by comparing the solubility product expressions for ZnS and PbS. The metal ion that requires fewer hydroxide ions for precipitation will have the lowest solubility product expression.
4. The pH needed to maximize precipitation of one ion and leave the other in solution is determined by the concentration of OH-. The metal ion that requires fewer OH- ions will precipitate first, leaving the other metal ion in solution. The approximate pH needed can be calculated using the concentration of OH-.
5. To check your work and confirm your calculations, you can substitute the calculated concentration of OH- back into the Ksp expressions and calculate the maximum concentration of the metal ion that can remain in solution.
If you need further guidance or want to review your work, you can post your calculations or equations, and I'll be happy to help you.