14. For the strong acid-weak base titration of ammonia by hydrochloric acid, find the pH after 15.0 mL of 0.100 M HCl has been added to 25.0 mL of 0.100 M NH3 solution. (Kb = 1.8 x 10-5)

The reaction we will use is:

NH3 (aq) + H+ (aq) NH4+ (aq)

For the stoichiometric calculation:

NH3 (aq) H+ (aq) NH4+ (aq)
INITIAL
0.0025mol
0.0015mol
0mol
CHANGE
-0.0015mol
-0.0015mol
+0.0015mol
FINAL
0.0010mol
0mol
0.0015mol

Next we must convert the amounts obtained in the I.C.E. grid to concentrations. To do this we must:

a) divide the number of moles of NH3 and of NH4+ by 0.015 L
b) divide the number of moles of NH3 and of NH4+ by 0.025 L
c) divide the number of moles of NH3 by 0.025 L and the number of moles of NH4+ by 0.015 L
d) divide the number of moles of NH3 and of NH4+ by 0.040 L