TBR Solubility and pH dependence

[LuminousTruth]

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Doesn't lowering the pH affect ALL solubility?

Lowering the pH means higher concentration of H ions. These H ions would more readily bond with [A-], therefore decreasing solubility.

Increasing the pH means higher concentration of OH ions. These OH ions would accept a proton from HA and thus form A- and H2O, therefore increasing the solubility.

TBR says the solubility of chloride salts do NOT show pH dependence while the solubility of sulfide salts DO show pH dependence?

Can someone explain to me why this is the case?

 

[epsilion11]

No it doesn't. In order to remember these effectively I always have to write out the chemical equation to see the equilibrium if there is one. H_2_S has a higher pKa value becauseit is not a strong acid, however, HCL has a low pKa value, making it a strong acid. Because there is no equilibrium for HCl, it will always deprotenate to completion, making pH a non-factor. however H_2_S is a diprotic weak acid so the equilibrium is:

H_2_S <---->HS^-^ + H^+^ and further HS^-^ <----> S^2-^ + H^+^

and because of these equilibriums if you increase the concentration of H^+^ ions in the solvent then you shift the equilibrium to the left, making it less soluble. However, by putting H2S in a basic solution, will create H20, decreasing the H+ ion concentration, which shifts the equilibrium to the right, making it more soluble. Make sense?

 

[LoLCareerGoals]

^ good explanation. This is a special case of the common-ion effect. Look it up.