end points and solution composition are made. These points have been considered in Chapter 3 and are
used in the indicator selection procedure outlined in the preceding section of this chapter.
Acid-base Titrations in Non-aqueous Solvents
Non-aqueous ionizing solvents can sometimes be used with advantage in acidimetry and alkalimetry. A
basic solvent can encourage the loss of a proton from a very weak acid making it effectively much
stronger. Similarly an acidic solvent can be used to amplify the basic nature of a solute. Manipulation of
these principles enables the scope of acidimetry and alkalimetry to be extended to compounds that
cannot be titrated in an aqueous medium. Standard reagents need to be selected with care as they must
resist attack by the solvent as well as functioning as an acid or base in the appropriate solvent system.
Tables 5.2 and 5.3 summarize data for nonaqueous titration media.
Table 5.2 Acidic solvents. Reagents: perchloric acid (acid) and potassium hydrogen phthalate (base).
Solvent Analyte Indicator
iso-propyl alcohol/ethylene glycol sodium carboxylates phenol red
acetic acid amines, heterocyclic bases, amides, urea crystal violet neutral red
nitromethane/acetic anhydride very weak bases methyl violet neutral redApplications of Acid-base Titrations
The importance of acids and bases in industrial processes is almost impossible to overstate. Correct pH
conditions are often essential to the progress of manufacturing reactions. At the same time, it may be
highly undesirable for the product to contain excessive acid or base. In the food and petroleum
industries, constant monitoring of acids and bases in both reaction mixtures and finished products is a
common requirement which titrimetric methods frequently fulfil. At the process control stage, automatic
methods are increasingly becoming the rule, and some details of such techniques are given in Chapter
- It is probable that the acidity or basicity present is derived from a mixture of acids or bases. The
convention of acid or base number is used to overcome any ambiguity that might arise in the expression
of acid or base content. Thus the acid or base content might be expressed as the number of milligrams of
sulphuric acid or potassium hydroxide equivalent to 1 dm^3 or 1 kg of the sample, irrespective of the
actual acids present. Acid-base titrations may be used also in analytical methods where the analyte reacts
to produce a stoichiometric amount of an acid or base which can then be titrated. Probably the most
well-known