A microcalorimetric study of the intermediate complexes CdBr+. CuBr+ in aqueous solution
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Panckhurst has attempted to explain the observed stability trends for a series of halide complexes in solution with a given metal and also for various complexes with a given halide. He concludes that the stabilities relative to one another are dependent upon the relative magnitudes of the standard heats of formation and standard entropy changes but that the data available is inadequate and often subject to factors which make comparison difficult. In recent years, increasing interest has been shown in the physical chemistry of complex-ion formation. In particular, numerous measurements have been made of the stability constants of complex ions and hence their free energies of formation. If their heats of formation are also known the corresponding entropy changes can, of course, be evaluated. Usually however, either these heats of formation have not yet been determined, or else the only values available are those calculated from stability – constant measurements at more than one temperature. The reliability of such values often seems questionable, primarily because the range of temperatures over which the measurements were made has almost always been too small. It is undoubtedly better to measure the heats of formation calorimetrically, preferably under more or less the same conditions of concentration and ionic strength as those used in the measurement of the stability constants. We here report a microcalorimetric determination of the heats of formation of the complex ions CdBr+ and CuBr+ in aqueous solution. The apparatus and procedure employed are similar to those used previously in this college in work on the lead halide complexes. In the case of the CdBr+ complex we have extended the method to calculate a value of the equilibrium constant which we shall compare with other values from the available literature. We shall attempt in conclusion to throw some further light on the nature of complex species in solution and also to further explain the observed stability trends of these complexes.