Acta Phys. -Chim. Sin. ›› 1987, Vol. 3 ›› Issue (02): 146-154.doi: 10.3866/PKU.WHXB19870208

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Ji Hongwei; Xie Wenhui   

  1. Department of Chemistry; Peking University; Beijing
  • Received:1985-11-16 Revised:1986-04-20 Published:1987-04-15

Abstract: The solubilities of o, m, p-xylene in water as well as in the aqueous salt solution were determined at 25 ℃ by spectrophotometer. The activity coefficient (f) of each of the xylenes has also been calculated. The salts used are LiCl, NaCl, KCl, SrCl_2, BaCl_2, LiBr, NaBr and KBr.
The salt concentrations (c_s) used are 0-1 mol L~(-1). When logf were ploted vs. c_s for eight salts, the obtained results are all straight lines. On comparison of the slopes of these 24 lines, the salting-out order is BaCl_2>SrCl_2>NaCl>KCl>NaBr≈LiCl>KBr>LiBr for each of the xylenes.
The salt effect constant k_s can be expressed in terms of the sum of k_+ and k_-. The values of k_ decreases with the increase of the dipole moment of the xylene molecule.
The salting-out constants of these xylenes in eight aqueous salt solutions have been calculated respectively by the formulas of (1) Debye-McAulay, (2) Conway-Desnoyers-Smith, (3) McDevit-Long and (4) modified internal pressure theory.
Some assumtions were made for the modified equation of the internal pressure theory. When the distance between ion and nonelectrolyte molecule in aqueous salt solution was calculated, Latimer′s radii are used instead of the Pauling′s radii of ions. For larger nonelectrolyte molecules, equation of the modified internal pressure theory (4) given results in better agreement with the experiment than those of (1), (2) and (3).