The effect of Me4NBr, Et4NBr, Bu4NBr, and (EtOH)3EtNBr on the Temperature of Maximum Density of Water

The densities of aqueous solutions of Me4NBr, Et4NBr, Bu4NBr, and Et(OH)(3)EtNBr were measured in the concentration range 0.002 to 0.05 mol.kg(-1). The temperature of the determinations ranged from 275.15 to 279.15 K in 0.5 K steps, and the uncertainty of the densities was around +/- 1 x 10(-6) g.cm(-3). Eleven concentrations were used for each of the salts. It was found that all the solutes follow Despretz' law. The absolute value of the Despretz's constants increases with increasing number of carbon atoms in the cation, except for Et( OH) 3EtNBr which has the highest value. The ionic contributions to the Despretz's constants were calculated. The volumetric data obtained allows the calculation proposed by Kalgud and Pokale. The effective ionic radii were calculated using a semi-empirical equation, as proposed previously by several workers. The nonlinearity of the plot of the ionic Despretz constants versus effective ionic radius is confirmed.