A thermometric titration utilizes the enthalpy change of the reaction involved to locate the end point. It has been defined as “a titration in an adiabatic system yielding a plot of temperature vs. volume of titrant.” The procedure consists of delivering the titrant from a thermostated buret into a solution contained within a thermally insulated vessel. and observing the temperature change of the solution either upon continuous addition, or after each successive incremental addition, of titrant.
Advantages
These temperature-volume plots resemble the corresponding graphs obtained from conductometric, photometric, and amperometric titrations. Yet while each of the latter three methods is severely limited to specific kinds of systems - e.g., conductometric titration requires electrolytic solutes in solvents of high dielectric constant, almost all reactions exhibit detectable enthalpy changes (positive or negative). This wide applicability, coupled with simplicity, suggests a potential increase in the use of thermometric titrations in analytical chemistry, particularly in those media in which electrometric and photometric methods are inapplicable.
The analytical sensitivity of the thermometric titration method is linearly related to concentration, in contrast to the logarithmic relation to concentration which exists for many other analytical methods, e.g., potentiometric methods. A linear relation is an advantage when very dilute solutions or solutions with high concentrations of interfering ions are being analyzed. For example, a pH titration of a solution containing pyridine at a concentration below 0.05 M will give a poorly defined end point, while the end point of a thermometric titration is well defined.
Applications
Neutralization
Weak acids and bases have been studied by several workers. Bell and Cowell recommended the use of thermometric titration for the preparation of neutral solutions of ammonium citrate. Linde, Rogers, and Hume titrated both weak and strong acids and bases, showing that clear end points were obtainable even in emulsions and thick slurries, and that a mixture of sodium hydroxide and sodium carbonate could be determined with good accuracy. Jordan and coworkers show that, unlike potentiometric titration which is dependent upon free-energy changes, thermometric titration works very well even for extremely weak acids. End points are precise and accurate for acids as weak as boric acid, because the enthalpy change of neutralization is not very different from that of a strong acid.
Complexation
The greatest number of papers on thermometric titration deal with investigations of complex formation, all of which are of analytical importance either directly or indirectly. For EDTA titrations, an accuracy within 3% is possible with cation concentrations as low as 0.0005 M.
