How do you calculate the expected change in pH of a buffer solution when acid/base is added?

A buffer of pH 4 is prepared by adding 0.14g of solid sodium ethaonate to 0.1l of 0.1mol/l ethanoic acid.

What will be the new pH if 2.2 mL of HCl are added?

If 4.5mL of NaOH are added?How do you calculate the expected change in pH of a buffer solution when acid/base is added?
Molar mass CH3COONa = 82 g/mol

Moles CH3COONa = 0.14 g / 82 = 0.00171

[CH3COONa]= 0.00171 / 0.1 = 0.0171 M

Ka = 1.8 x 10^-5

pKa = - log 1.8 x 10^-5 = 4.74

pH = pKa + log [CH3COO+]/ [ CH3COOH ] =

= 4.74 + log 0.0171 / 0.1 = 3.97



The effect of the added HCl would be to decrease the moles of CH3COO- and increase the moles of CH3COOH.

But I have to know MOLARITY of HCl to get pH

In the same way the effect of the added NaOH would be to increase the moles of CH3COO- and decrease the moles of CH3COOH , but I have to know the molarity of NaOHHow do you calculate the expected change in pH of a buffer solution when acid/base is added?
depends on what the normality is of the HCL/NaOH
pKb of Ch3COOH is required.