[OrthoParaDirector]

Hello,

I found this wiki page with the solubility of a lot of compounds.

http://en.wikipedia.org/wiki/Solubility_table

These solubilities are all under neutral conditions. I would like to know if it is possible to calculate how the solubility would change if the pH would change.

For example Cu(I)₂S has a solubility of 1.361E-15 (g/100 ml at 20 degrees Celsius).

How would this value change if the pH would be low (pH =1) for example? Is there a way to calculate or to estimate this?

I am interested in solubility at pH change in general. This is just an example

Thanks.

[Borek]

Use Ka values to calculate what part of sulfide is in the S^2- and HS^- form, then remember that from mass balance concentration of copper is twice sum of concentrations of all forms of sulfide (S^2-, HS^- & H₂S). That will give you a set of equations. "Just" solve.

[OrthoParaDirector]

After some Internet research I found the following:

Cu₂S(s) <--> 2Cu⁺ + S2^- Ksp = 3×10-49

S₂^- + H₂O <--> OH^- + HS^- Kb1 = 0.79

HS^- + H₂O <--> OH^- + H₂S Kb2 = 1.05×10-7

In your last post you've said: "then remember that from mass balance concentration of copper is twice sum of concentrations of all forms of sulfide"

The mass balance equation should become the following:

[Cu⁺] = 2[S^2-] + 2[HS^-] + 2[H₂S]

but why? Why not:

[2Cu⁺] = [S^2-] + [HS^-] + [H₂S]

Thanks in advance

[Borek]

Think about dissolution stoichiometry.

Try some simpler example - 1M solution of Na₂S. Ignore S^2- hydrolysis. What is concentration of Na⁺? Of S^2-? Which is twice the other?

[OrthoParaDirector]

The concentration of sulfide is twice the sodium concentration. But it still confuses me..

[Borek]

The concentration of sulfide is twice the sodium concentration. But it still confuses me..

Is it? 1M Na₂S solution contains 2M Na⁺ and 1M S^2-.