[kemystery]

Hi guys.

I'm trying to get my head around the fact that a solution is basic after neutralization of a weak acid with a strong base. It's supposed to be because the correspondent base will dissociate with water, so let's see:

CH₃COOH + NaOH  CH₃COO^- + Na⁺ + OH^-

So we add NaOH until it has been neutralized. But then I learn that the high pH value comes from:

CH₃COO^- + H₂O  CH₃COOH + OH^-

Would this not mean we can in fact never neutralize acetic acid, there will always be some in the solution? But we say that at the steep titration curve, we have now neutralized the initial acetic acid that was present, or something? Thank you very much!

[Borek]

I'm trying to get my head around the fact that a solution is basic after neutralization of a weak acid with a strong base. It's supposed to be because the correspondent base will dissociate with water, so let's see:

CH₃COOH + NaOH  CH₃COO^- + Na⁺ + OH^-

Apart from the fact the equation is not balanced, you got it wrong. Solution of the weak acid salt (which is what you get after you neutralize the acid) is basic, because the acid's conjugate bate reacts with water. What is the conjugate base of acetic acid?

So we add NaOH until it has been neutralized. But then I learn that the high pH value comes from:

CH₃COO^- + H₂O  CH₃COOH + OH^-

Would this not mean we can in fact never neutralize acetic acid, there will always be some in the solution? But we say that at the steep titration curve, we have now neutralized the initial acetic acid that was present, or something? Thank you very much!

At equivalence point we added stoichiometric amount of the base. But yes, there is some minute equilibrium amount of the undissociated acid still present in the solution. Nothing that can be done about it - even after adding excess base there will be some small amount of acid present (the higher the pH, the lower its concentration, but technically it never equals zero).

[kemystery]

AH yes I wrote it up incorrectly. But you managed to clarify anyway, so thanks a lot!