Solubility of tartaric acid/sodium tartrate in high vs low pH

[roneddy]

Homework Statement

So we did a lab in organic chemistry where we did a resolution experiment for enantiomers and in the separatory funnel we had sodium tartrate/tartaric acid left in the aqueous phase of the funnel. It asks why this compound is more soluble in high ph solutions as compared to low ph solution.

Homework Equations

H2C4H4O6(aq) + H2O(l) = H30+(aq) + HC4H4O6-(aq) - disassociation reaction

3. The Attempt at a Solution

The only think i could think of was in terms of le chatelier's principle where you dissociate less in a low ph solution due to excess H+ already present pushing equilibrium towards the reactants, while in a high ph solution the OH- will react with the H+ pushing equilibrium towards the products.

 

[Bystander]

The only think i could think of was in terms of le chatelier's principle where you dissociate less in a low ph solution due to excess H+ already present pushing equilibrium towards the reactants, while in a high ph solution the OH- will react with the H+ pushing equilibrium towards the products.

Bingo.

 

[epenguin]

Ognib! I don't think that answer even if what it says is true is actually by itself explaining anything about the solubility..

About your formula by the way the pK_as of tartaric acid are 2.9 and 4.4 so at high pH it will be doubly dissociated.

 

[roneddy]

I really can't think of anything else that would allow it to be more soluble in high ph as compared to low ph.

 

[epenguin]

I'm not saying it needs another explanation, I'm saying it needs an explanation. Yours does not amount to an explanation. Maybe there was one in your head and you have forgotten to write some essential part of it.

For what you say about reactants and products, Well what you call reactants and what you call products is arbitrary. Write your equation the other way round and products become reactants and vice versa. Then the same words that you use would give the opposite conclusion.

 

[Bystander]

Ognib!

Phenol solubilities in successively stronger bases, bicarbonate < carbonate < hydroxide; I say again, "Bingo."