Question

What is the fraction of HA dissociated at a pH of 6.10 if Ka = 1.8 x 10-5? 0% 4% 100% 96%

Which of the following is true about the shape of the titration curve for a 0.1 M weak acid being titrated with a 0.2 M strong base as compared to a 0.1 M strong acid being titrated with a 0.2 M strong base?

The equivalence point volume will shift to the left.

It will start at a lower pH.

The equivalence point pH will be larger.

The equivalence point volume will shift to the right.

What is the volume at the equivalence point when 30.0 mL of 0.25 M HCl are titrated with 0.40 M NaOH at T = 298 K? K_w = 1.00 x 10^-14.

18.8 mL

30.0 mL

7.00 mL

37.6 mL

Answer 1

1)

pH = 6.10

[H+] = 10^-pH

        = 10^-6.10

        = 7.94 x 10^-7 M

Ka = [H+]^2 / C

1.8 x 10^-5 = (7.94 x 10^-7)^2 / C

C = 3.50 x 10^-8 M

fraction of HA dissociated = H+ x 100 / C

                                          = 7.94 x 10^-7 x 100 / 3.50 x 10^-8

                                          = 100%

answer : 100%

2)

answer : The equivalence point pH will be larger

3)

volume = 30 x 0.25 / 0.40 = 18.75 mL

answer : 18.8 mL