You prepare a solution from 10.0 mL of 0.100 M MOPS buffer (3-morpholinopropane-1-sulfonic acid) and 10.0 mL of 0.071 M NaOH. Next, you add 1.00 mL of 1.89 × 10-5 M lidocaine to this mixture Denoting lidocaine as L, calculate the fraction of lidocaine present in the form LH .

Answer 1

First calculate the pH of the buffer prepared with MOPS and NaOH.
10 mL x 0.1 MOPS acid = 1.0 mmoles.
10 mL x 0.071 = 0.71 mmols NaOH

......MOPSacid + OH^- ==> MOPSbase + H2O
I......1..........0.........0
add.............0.71..........
C......-0.71...-0.71........0.71
E.......0.29......0.........0.71

I have the pKa for MOPS to be 7.20 but use the value in your text/notes.
pH = 7.20 + log(base)/(acid)
I estimate pH = 7.60 or (H^+) = about 2.58E-8

Then Ka for lidocaine I have as about 4E-8 but use the value in your text/notes.
.......HL ==> H^+ + L^-
fraction in HL is alpha zero (Ao).
Ao = (H^+)/[(H^+)+(Ka)]
You know (H^+) from the buffer and you know Ka, solve for Ao.

Answer 2

Don't listen to these idiots the answer is actually .773.