Write an equilibrium reaction for a buffer system made of the weak base, B, and its conjugate acid. If the buffer contains 1.05 M of B and 0.750M conjugate acid and has a pH of 9.50, what is the pH after 0.0050 mol HCl is added to 0.500 L of this solution?

Answer 1

B + H^+ ==> BH^+

In 500 mL of the buffer we have millimols of
B = 500 x 1.05 = 525
BH^+ = 500 x 0.750 = 375
add 0.005 = 5 millimols HCl.

...........B + H^+ ==> BH^+
initial...525.........375
add............5..............
change.....-5...-5....5
equil.....520.....0....380

Plug into the Henderson-Hasselbalch equation and solve for pH.