1)
millimoles of pyridine = 25.0 x 0.125 = 3.125
concentration of HCl = 0.100 M
Kb = 1.7 x 10^-9
pKb = 8.77
a) at half -
equivalence point :
pOH = pKb
pOH = 8.77
pH = 5.23
b) at 40 mL of added
acid.
mmoles of HCl = 40 x 0.100 = 4
C5H5N  +  HCl Â
----------------> C5H5NH+
3.125Â Â Â Â Â Â Â Â Â
4Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0
   Â
0Â Â Â Â Â Â Â Â Â Â
0.875Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
3.125
here strong acid remains.
[H+] = 0.875 / 40 + 25 = 0.01346 M
pH = -log (0.01346)
pH = 1.87
c) 50 mL of added
acid.
pH = 1.60
