|Below is a graph depicting the changes that occur in the
pH of a
solution during a titration of a typical strong acid with a typical
|At the start, before any NaOH has been added, the solution
25.00 mL of 0.20 M HCl. Since the HCl is a strong acid and is 100%
the initial pH is quite low.
|As we add more and more NaOH solution we are of course
the concentration because of volume changes. Between 0 and
24 mL of NaOH added, a large increase in the pH is not seen. All that
happening is that the added base is changing some of the acid to the
NaCl. NaCl, neither of which ions hydrolyses, so the concentration of
acid gradually becomes more and more dilute. By adding just enough base
to neutralize the acid the pH should change drastically to a pH of 7.00
or neutrality. The addition of a little more base will cause the
solution to become quite caustic.
|The graph above indicated that a rapid change in pH with a
change in volume of standard solution is desirable if the indicator is
to give a sharp colour change at the endpoint.