How to calculate pH change (buffers)?

Calculate the pH change that occurs when 1.0mL of 1.0M HCl is added to:

a. 1.0 L of pure water and

b. 1.0 L of acetic acid/sodium acetate buffer with [CH3CO2H] = 0.70M and [CH3CO2-] = 0.60M.

How to calculate pH change (buffers)?
moles HCl = 0.0010 L x 1.0 M = 0.0010



a.

pH of pure water = 7.0

total volume = 1.001 L

[H+] = 0.0010 / 1.001 L = 0.000999 M

pH = 3.00

pH change = 7.0 - 3.0 = 4.0



b.

pH of the buffer = pKa + log [CH3COO-] / [CH3COOH]

pH = 4.74 + log 0.60 / 0.70 = 4.67

after 1.0 mL of HCl is added :

CH3COO- + H+ = %26gt; CH3COOH

moles CH3COO- = 0.60 - 0.0010 =0.599

[CH3COO-] = 0.599 / 1.001 L =0.598 M

moles CH3COOH = 0.70 + 0.0010 = 0.701

[CH3COOH] = 0.701 / 1.001 = 0.700 M

pH = 4.74 + log 0.598/ 0.700 = 4.67

no change