Dissociation Equilibria of Spherical and Disk-Shaped Ions in Sulfur Dioxide Solution
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Conductivity data have been obtained for solutions in liquid sulfur dioxide for ionophores composed of either spherically symmetrical or planar ions. Established methods have been employed to secure thermodynamic equilibrium constants (Kesp.) and limiting equivalent conductances from the data. By arbitrarily adopting the crystallographic radius of the potassium ion as both its radius of closest approach in ion pairs and its hydrodynamic radius in liquid sulfur dioxide solution and assuming that the radius of an ion is independent of its counter ion, three "radii" can be assigned to each ion: (1) R(cryst.), the crystallographic ionic radius of elemental ions and, for other ions, the radius calculated from bond distances and angles and van der Waals radii; for planar ions this is taken as the longest radius about the center of gravity. (2) R(SO2), the Bjerrum radius, calculated from Kexp. by means of Bjerrum's equation. (3) R(Stokes), the hydrodynamic radius calculated from the limiting equivalent conductances by means of Stokes' equation. Values of the three radii are assembled in Table I. Agreement among the various radii of the anions is remarkable. In every case excellent agreement is found among R(Stokes), R(cryst.), and R(SO2), except for BF4- and CLO4-. For each of the latter two ions R(SO2) is virtually identical with the van der Waals radius of oxygen (1.4A) and fluorine (1.35A) respectively. For most of the cations, R(SO2) is in excellent agreement with R(cryst.). However, R(Stoked) for each of these cations is much smaller than R(SO2) or R(cryst.). It has therefore been established that for liquid sulfur dioxide surprisingly good agreement is observed between Bjerrum distances of closest approach (a) calculated from Kexp. and sums of ionic radii for both spherical and disk shaped ions. Further, the mobility of the anions measured is accurately predicted by Stokes Law assuming crystallographic or van der Waals radii. Solutions of potassium bromide have been measured at five temperatures providing, together with earlier work, data at seven temperatures in the range of +0.12 degrees Celcius to -24.99 degrees Celcius. Delta Hexp. is found to be constant over this temperature range, with a value of -4.77 Kcal/mole. [TRUNCATED]
Thesis (Ph.D)--Boston University
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