[Super Newb]

Given that sodium acetate is a salt and is highly soluble in water, I am wondering how will the change in the pH of the media affect the solubility of the salt.

My postulation is as such:

CH3COONa ----> CH3COO- + Na+    (fully dissociated)
CH3COO- + H2O <---> CH3COOH + OH-  (equilibrium)

Hence, in low pH condition, H+ will increase and hence scavenge OH-. The equilibrium for the second equation will be shifted to the right and hence forming more acetic acid (uncharged) and decreasing the solubility of the salt.

In the case for Aniline Hydrochloride, it is a salt and is highly soluble in water. Hence the equations can be written as such:

ArNH2.HCl ---> ArNH3+ + Cl-     (fully dissociated)
ArNH3+ + H2O <---> ArNH2 + H3O+ (equilibrium)

Hence, in low pH condition, H+ will increase. The equilibrium for the second equation will be shifted to the left and hence forming more aniline cation (soluble species) and increasing the solubility of the salt.

Many of my colleagues have answers that contradict mine, so I'm wondering if the above explanation is correct.

[mjc123]

The equilibrium for the second equation will be shifted to the right and hence forming more acetic acid (uncharged) and decreasing the solubility of the salt.

Why would that decrease the solubility of the salt?

[Super Newb]

You are right, it is true that acetic acid is miscible with water even when it's uncharged. Hence, would you say that the solubility of sodium acetate is unaffected by the pH of the media? How about in the case for aniline hydrochloride?

[mjc123]

You're missing the point. If the second equilibrium is shifted to the right, [AcO^-] is reduced and the first equilibrium is shifted to the right.

[Super Newb]

CH3COONa (s) <---> CH3COO- (aq) + Na+(aq)    (equilibrium)
CH3COO- + H2O <---> CH3COOH + OH-  (equilibrium)

If it is in accordance what was stated, the equilibrium of the second equation shifts the right as pH of the media is lower and [AcO-] decreases. As a result, the equilibrium for the first reaction is shifted to the right hence increasing its solubility?

Similar for the aniline hydrochloride,

ArNH2.HCl (s) <---> ArNH3+ (aq) + Cl- (aq)  (equilibrium)
ArNH3+ + H2O <---> ArNH2 + H3O+ (equilibrium)

as the pH of the media decreases, the equilibrium for the second reaction is shifted towards the left and thus producing more [ArNH3+]. As more [ArNH3+] is formed, the equilibrium for the first equation is shifted left and hence reducing its solubility?

[AWK]

Your problems concern hydrolysis of salts or buffer solutions.

[Super Newb]

Hi AWK,

Thanks for the comment. I was referring to the hydrolysis of the salt instead of the buffer.

[AWK]

If you change pH of hydrolysing salt, the problem changes to a buffer solution.