Validity of the correlation-Belda equation for some physical and chemical properties in isobutyric acid plus water mixtures near and far away from critical temperature

Knowledge and prediction of physicochemical properties of binary mixtures is of great importance for understanding intermolecular interactions. The literature shows that most of such systems exhibit non-linear behaviour. In this frame, a correlating equation with two parameters is recently proposed by Belda and tested with success for about of 50 binary systems for density, viscosity, surface tension and refractive index. In order to assess the validity of the proposed equation, the latter has been applied to isobutyric acid+water mixtures (at 300.15 or 301.15 and 308.15 K) for seven physicochemical properties. These mixtures exhibit strong correlations and interactions, especially near the critical composition and temperature. Experimental results are compared with those fitted with the proposed equation in the light of the corresponding correcting factor. On the whole, the Belda equation seems to offer satisfactory results for some properties even near critical temperature when interaction and correlation length between molecules increases.