Find the pH for a mixture of 20ml 0.5M CH3COOH and 25ml 0.5M NaOH? (pKa of CH3COOH = 4.74)?

Answer 1

20ml 0.5M CH3COOH ==> 10 mMole CH3COOH
25ml 0.5M NaOH ==> 12.5 mMole NaOH.
Since one mole of CH3COOH reacts with one mole of NaOH based on the following reaction:
CH3COOH + NaOH ==> CH3COONa + H2O
there will be 2.5 mMole NaOH left in 45 ml solution, which is 0.0556M NaOH
pH = 14 + log(0.0556) = 12.7