Question

Your acid has a pka of 7.54 and a concentration of 0.084M. You are given 38.6mL of this acid, what is the pH of this initial solution? Calculate the pH of the solution after adding 8.7, 17.1, 30.5, and 33.3 mL of 0.100M NaOH. At the equivalence point, what volume of base is added and what is the pH?

Answer 1

a ) initial pH :

pH = 1/2 [pKa -logC]

pH = 1/2 [7.54 -log 0.084]

pH = 4.31

b) volume of base at equivalece point :

at equivalece point : miilimoles of acid = millimoles of base

acid millimoles = 0.084 x 38.6 = 3.24

3.24 = millimoles of base

3.24 = 0.1 x V

32.4 mL = V

at equivelce point volume of base = 32.4 mL

c) 8.7 mL added

acid millimoles = 3.24

base millimoles = 8.7 x 0.1 = 0.87

acid + base --------------------> salt

3.24      0.87                            0 ----------------> initial

2.37      0                                0.87 -------------> after reaction

pH = pKa + log [salt/acid]

pH = 7.54 + log (0.87/2.37)

pH = 7.10

d) 17.1 mL added

acid millimoles = 3.24

base millimoles = 17.1 x 0.1 = 1.71

acid + base --------------------> salt

3.24      1.71                            0 ----------------> initial

1.53      0                                1.71 -------------> after reaction

pH = pKa + log [salt/acid]

pH = 7.54 + log (1.71 / 1.53)

pH = 7.59