Question #c1b5b

1 Answer
Nov 21, 2016

Answer:

The pH of a buffer solution depends on the ratio of concentrations of an acid and its conjugate base, using the Henderson-Hasselbalch equation.
#pH=pK_a-log_10(([HA])/([A^-]))#

Explanation:

In this example, the acid is #NH_4^+#, which has a #pK_a=9.24#

Total volume of solution = 30mL + 15 mL = 45 mL = 0.45 L

Acid concentration: #(0.1M times 0.015L)/(0.045L) = 0.033M#

Base concentration: #(0.2M times 0.030L)/(0.045L) = 0.133M#

#pH=pK_a-log_10(([HA])/([A^-]))=9.24-log_10(0.033/0.133)=9.84#

Sanity Check:
If the acid and base concentrations were equal, the #pH# would be equal to the #pK_a#, but here the base concentration is 4X the acid concentration, so the solution is a little bit more basic and the #pH# is a little bit higher than #pK_a#.