Ksp with significant anion hydrolysis

[Qube]

No, they are not. I explained it at least once, your prof explained it as well, you are still surprised?



You can calculate Ksp from the molar solubility, just not directly. Knowing just molar solubility you can easily calculate formal concentrations, but not equilibrium concentrations - for these you need additional information about dissociation constants. Once you find equilibrium concentrations, you can calculate Ksp value.

"Naive" approach - treating formal concentrations as equilibrium concentrations - is a sure way of getting wrong Ksp value.

We are going in circles, I feel like I am wasting my time repeating the same again and again.

I see what you're saying. We have to take in account Kb (of the phosphate anion) in addition to the formal concentration. Is that your point?

 

[Borek]

We have to take into account ALL possible reactions that can change equilibrium concentrations of the ions produced in the dissolution.

 

[Qube]

Thanks for clarifying everything. I think I understand now and if anything we agree that the original Ksp value for Silver Phosphate is likely unreliable. And the other things we've learned:

1) The IUPAC definition of Ksp as being not the product of "constituent" ions but the products of dissolution equilibria with due reference to said dissolution equilibria.

2) Analytical equilibrium: always consider all relevant equilibria.