Calculate the pH of the following solutions:
a. a buffer made from a mixture containing 0.125 mol dm-3 of CH3COO- and 0.252 mol dm-3 CH3COOH (pKa = 4.76)
b. a buffer made when 0.350g of sodium ethanoate, CH3COO-Na+, is dissolved in 100 cm3 of 0.100 mol dm-3 CH3COOH (pKa = 4.76)
c. a buffer made by mixing 100 cm3 of 0.200 mol dm-3 CH3COOH (pKa = 4.76) with 30 cm3 of 0.400 mol dm-3 NaOH.