Isopiestic determination of the osmotic and activity coefficients of dilute aqueous solutions of symmetrical and unsymmetrical quaternary ammonium bromides with a new isopiestic cell at 298.15Â K

The osmotic coefficients of Bu4NBr, sec-Bu4NBr, iso-Bu4NBr, Bu2Et2NBr and Bu3EtNBr were determined by isopiestic method at 298.15 K in dilute aqueous solutions. A branched isopiestic cell was used. The osmotic coefficients of tetra-alkyl-ammonium solutions were analyzed comparing these with the Debye-Hückel limiting law. The order of the osmotic coefficient variation is Bu2Et2N+ > BuEt3N+ > sec-Bu4N+ > iso-Bu4N+ > n-Bu4N+. The results were fitted to the Pitzer equation and the parameters β0 and β1 were calculated. The results are discussed.