20 ml of 0.2 M NaOH is added to 50 ml, of 0.2 M CH3COOH to give 70 ml, of the solution. What is the pH of the solution ? The ionization constant of acetic acid is 2 × 10-5

The addition of NaOH converts equivalent amount of acetic acid into sodium acetate. Hence,Concentration of acetic acid after the addition ofNaOH = 3070  ×  0.2 MConcentration of CH3COONa after the addition of NaOH = 2070  ×  0.2 MHence, using the expressionpH= pKa + log  SaltAcid=-log  2 × 10-5 + log 23 = 4.699 - 0.177 = 4.522