Barrons SAT Subject Test Chemistry, 13th Edition

H+(aq) + OH−(aq) → H 2 O(l)

until all the OH− was neutralized; then the excess H+ caused the litmus paper to
change color.
To solve the question of the concentration of NaOH, this equation is used:

Macid × Vacid = Mbase × Vbase

TIP

For a titration:

Macid × Vacid =

MBase × VBase

Substituting the known amounts in this equation gives

In choosing an indicator for a titration, we need to consider whether the
solution formed when the end point is reached has a pH of 7. Depending on the
types of acid and base used, the resulting hydrolysis of the salt formed may cause
the solution to be slightly acidic, slightly basic, or neutral. If a strong acid and a
strong base are titrated, the end point will be at pH 7, and practically any
indicator can be used because adding 1 drop of either reagent will change the pH
at the end point by about 6 units. For titrations of strong acids and weak bases, we
need an indicator, such as methyl orange, that changes color between 3.1 and 4.4
in the acid region. When titrating a weak acid and a strong base, we should use an
indicator that changes in the basic range. Phenolphthalein is the suitable choice
for this type of titration because it changes color in the pH 8.3 to 10.0 range.
The process of the neutralization reaction can be represented by a titration
curve like the one below, which shows the titration of a strong acid with a strong
base.