Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

The shape of the titration curve depends on the strength of the acid in solution. After the point of equivalence

the shape is nevertheless identical but before the shape is characteristic for the acid strength. The climb of the

titration curve is more step for the weak acid than for the strong acid. The levelling-off of the curve for the

weak acid is caused by the buffer effect as earlier emphasised. A buffer system functions optimal when [HA]

= [A-] which is exactly half way to the equivalence point. This is way the weak acid titration curve here is

more flat than it is the case for the strong acid at the same location.

Of other differences between the titration curves for the weak and the strong acid may be pointed out that the

pH value for the equivalence point is different. For the titration of the strong acid the point is at a pH value of

7.0 whereas the point of equivalence is in the basic region due to the corresponding weak base strength. It is

important to note the point of equivalence is defined on the basis of stoichiometry and not from pH. The

general shapes of titration curves for the titration of strong and weak acids may be seen from figure 5-3 A)

and B).

Figure 5- 3: Different titration curves

General shapes of titration curves for the titration of a strong acid with a strong base A) and the titration of

a weak acid with a strong base B).

5.6.1 Titration of polyprotic acids

So far we have only looked at titration of acids capable of removing one H+ ion. The tritration of polyprotic

acids requires in principles calculations of pH similar to our prior examples although one must keep track of

more things. This we will further look into in the following example.

Acids and bases