Question

Cacodylic acid is a common weak acid used to buffer biochemical reactions and has a pKa of 6.2. If you were to make a 1 L buffer of 100 mM cacodylic acid at pH 6.7, what volume of 5 M NaOH is needed to make this? Show your calculations

Answer 1

pH of acidic buffer = pka + log(base(or) salt/acid)

pka = 6.2

pH = 6.7

total no of mol of buffer = 1*100*10^-3 = 0.1 mol

no of mol of base(NaOH) = x mol

no of mol of carboxylic acid = 0.1 -x mol

6.7 = 6.2 + log(x/(0.1-x))

x = 0.078 mol

no of mol of base(NaOH) = x = 0.078 mol

volume of NaOH must take = n/M = 0.078/5 = 0.0156 L

                        = 15.6 ml