A CRITICAL-REVIEW OF METHODS FOR OBTAINING IONIC VOLUMES IN SOLUTION

The various major methods for obtaining individual or ''absolute'' ion ic standard partial molar volumes (V) over bar(o)(ion) from whole elec trolyte data in both aqueous and nonaqueous solutions are critically r eviewed. A number of undetected errors in previous analyses are pointe d out, and it is demonstrated that the reported agreement amongst the various methods in aqueous solution is largely fortuitous. All methods are shown to be unsatisfactory to varying degrees, with the reference electrolyte approach, using an electrolyte such as tetraphenylarsoniu m tetraphenylborate, appearing to be the least objectionable of those currently available. It is recommended that, subject to future theoret ical and experimental developments, the assumption that, at 25 degrees C: (V) over bar(o)(Ph4As+) - (V) over bar(o)(BPh4) = 8 cm(3)-mol(-1), or its equivalent: (V) over bar(o)(Ph4P+) - (V) over bar(o)(BPh4-) = 2 cm(3)-mol(-1) be used in all solvents.