equivalence point, a slight difference in pH between it and the endpoint translates to a minuscule
difference in VB.
BASIC CONCEPT
An indicator is a weak organic acid or base that has different colors in its undissociated and
dissociated states. The indicator used most frequently in Intro Chemistry labs is
phenolphthalein, which is colorless at low pH but turns red around a pH of 8.WEAK ACID AND STRONG BASE
Titration of a weak acid, HA, with a strong base produces the following titration curve:
Comparing this figure with the previous one shows that the initial pH of the weak acid solution is
greater than the initial pH of the strong acid solution. The equivalence point is in the basic range.
This is consistent with what we discussed earlier about the salt of such a titration being a base.
BUFFERS
A buffer solution consists of a mixture, in roughly equal molar quantities, of a weak acid and its salt
(which consists of its conjugate base and a cation), or a mixture of a weak base and its salt (which
consists of its conjugate acid and an anion). Two examples of buffers are: a solution of acetic acid
(CH 3 COOH) and its salt, sodium acetate (CH 3 COO−Na+); and a solution of ammonia (NH 3 ) and its salt,
ammonium chloride (NH 4 +Cl−). Buffer solutions have the useful property of resisting changes in pH
when small amounts of acid or base are added.