Calculate the volume of ).1 M NaOH solution you need to add to 50.0 ml of 0.1 M CH3COOH solution to form a buffer ph 4?

Question

abb0t · Answer

I think you're missing some information here, you need the pKa of acetic acid. But anyway, you can use the henderson-hasselbach equation here to find the concentration and finally, get the volume. 

$\sf \color{red}{pH = pK_a + log[\frac{A^-}{HA}]}$

$\sf \color{blue}{pH-pKa = log(\frac{[A^-]}{[HA]})}$

$\sf \color{purple}{10^{(pH-pK_a)}=\frac{[A^-]}{[HA]}}$

find your expression for [HA] = 0.005-x
the 0.005 moles comes from: 0.1M$\times$(0.05 L)
remember, M = $\sf \frac{mol}{L}$

abb0t · Answer

If you have K$_a$, you can get pKa bu taking the -log(K$_a$)