Question

Why neutralization of acetic acid does not occur with sodium hydroxide in presence of hydrochloric acid?

Answer 1

See below

Explanation:

Sodium hydroxide is looking for `H^+` ions. More accurately, `OH^-` ions are looking for `H^+` to neutralize to water, `H_2O`.

Acetic acid is a weak acid with a `K_A = 1.8xx10^-5`
A little math trickery and this turns out to be:
`K_A = "Products"/"Reactants" = 1/"55,55"`
This means you get `1H^+`, and 55,555 Acetic Acids
It means Acetic acid doesn't fall apart very well.

HCl, on the other hand, completely falls apart. If you have 55,555 HCl, then you'll have 55,555 `H^+`

So, when `OH^-` are running around, they neutralize with the HCl first, since HCl gives its `H^+` up immediately. After all the HCl is neutralized, then the Acetic Acid will also neutralize, if you have `OH^-` left over.