Consider a solution that contains both C6H5NH2 and C6H5NH3+. Calculate the ratio [C6H5NH2]/[C6H5NH3+] if the solution has the following pH values. (Assume that the solution is at 25°C.)

Question

(a) pH = 4.70


(b) pH = 5.26


(c) pH = 5.42


(d) pH = 4.96

Answer 1

pKb = 8.77
use the Handerson-Hasselbalch equation
pOH = pKb + log [C5H5NH+]/ [C5H5N]

1
pOH = 14 - 4.50= 9.50
9.50 - 8.77=0.73
10^0.73 = 5.4 = [C5H5NH+]/ [C5H5N]
[C5H5N]/ [C5H5NH+]= 1 / 5.4=0.19