Question

Calculate the change in ph when 0.26 mol H+ is added to 1.00 L of each of the following buffers: a) a 0.58 M solution of pyridine (py) containing 0.52 M pyH+ b) a 0.58 M solution of aniline (an) containing 0.90 M anH+

Answer 1

pKb of pyridine is 8.75.

a) pOH = pKb + log [salt] / [base]

pOH = 8.75 + log (0.52 / 0.58)

pOH = 8.70

PH = (14 - 8.70) = 5.3

after addition of H+ ion,

pOH = 8.75 + log [(0.52 + 0.26) / (0.58 - 0.26)] = 9.14

pH = 14 - 9.14 = 4.86

pH change = 4.86 - 5.30 = -0.44

b) pKb of aniline = 9.37

pOH = pKb + log [salt] / [base]

pOH = 9.37 + log (0.90 / 0.58)

pOH = 9.56

pH = (14 - 9.56) = 4.44

after addition of H+,

pOH = 9.37 + log [(0.90 + 0.26) / (0.58 - 0.26)] = 9.93

pH = (14 - 9.93) = 4.07

pH change = (4.07 - 4.44) = - 0.37