How do you solve chemistry buffer problems?

1 Answer
Aug 18, 2016

Answer:

#pH=pK_a + log_10{[[A^-]]/[[HA])}#

Explanation:

See this old answer..

As you have probably heard ad nauseaum, at the point of half equivalence in the titration weak acid with a strong base, #[A^-]=[HA]#, and the expression #log_10{[[A^-]]/[[HA])}# #=# #log_10(1)=0#.

Going back to the equation, this means that #pH=pK_a# at the point of half equivalence in a strong base/weak acid or strong acid/weak base titration.

Problems are usually composed so that the formation of a buffer is not immediately obvious. For example, we may start with some concentration of say, acetic acid, #HOAc#, and #1/2# an equiv of sodium hydroxide is added. If the #pK_a# of acetic acid #=# #4.76# (which it does), then what is the #pH# of the given buffer?