PARTIAL MOLAL VOLUMES OF SULPHONIC ACIDS IN WATER SOLUTION

The partial molal volumes of methane-, benzene-, m-benzenedi-, tolyl- and p-toluenesulphonic acids in water solution have been determined by a buoyancy method. Since the concentration of sulphonic acids in water solution used in this experiment was extremly dilute, the partial molal volume _??_0 might be identical with the apparent molal volume φ. The latter can be determined from the specific gravities and concentrations of the sulphonic acid solutions from the following equation: φ=(V-n1V0)/n2 (1) where, V is the total volume of solution containing n1 moles of water and n2 moles of solutes, V0 the volume occupied by a mole of pure water.An attempt has been made to estimate the partial molal volume of imaginary ion, -SO3-, in water solution on the basis of simple model. The partial molal volume of imaginary ion, -SO3-, has been deduced to 35ml/mole from the experimental data.The deduced value for -SO3- is considerably larger, but lower than the calculated value, 52ml/mole, from the bond distance of S-O, and the van der Waals' radius of oxygen following the treatment of Mukerjee. This discrepancy has been explained in terms of an “effective charge”, which is higher than the formal charge. The considerably larger partial molal volume of -SO3-, deduced from the experimental data, indicates that the water structure surrounding the imaginary ion may be broken by the weak ion-dipole interaction.