Question

What is the pKa of buffer solution `HC_2H_3O_2` when HCl is added?

(HCl is part A)
part B: What about when NaOH is added?

(Google didn't tell me anything lol)

Answer 1

Look at the buffer equation....and we address `pH` NOT `pK_a`, the which is the acid dissociation constant....`pK_a` `HOAc=4.76`.

Explanation:

A buffer is where a weak base, and its conjugate acid are mixed together in appreciable quantities to give a solution that resists gross changes in `pH`...and for such a system...

`pH=pK_a+log_10{[[A^-]]/[[HA]]}`

In this scenario, where acetic acid is used as the acid...

`pH=4.76+log_10{[[OAc^-]]/[[HOAc]]}`

Addition of acetic acid OR acetate ion (OR `H_3O^+` or `HO^-`) should change the `pH` of the solution only marginally. What will be the `pH` of the buffer if `[""^(-)OAc]=[HOAc]`