Hydrogen isotope effects in the dehydration of polystyrene-divinylbenzene type ion-exchange resins and the structure of electrolyte solutions. 2. Na+, K+, and Cs+ forms of variously cross-linked Dowex 50W resins

Hydrogen isotope effects in the dehydration of sodium, and cesium forms of strongly acidic polystyrene-divinylbenzene type ion exchangers (Dowex 50W) of various cross-linkings (2-12% DVB content), containing varying amounts of water (1-26 mol of water per equivalent resin, n/sub w/), have been determined at 353 K by using a Rayleigh distillation type technique. In all the three cases, the single stage factors, α/sub MR/ (M = Na+, K+, or Cs+), at n/sub w/ < 3 were lower than α/sub w/, the single stage factor for water distillation at the same temperature. In this region of n/sub w/, α/sub NaR/ = α/sub KR/ < α/sub CsR/. The separation factor increases beyond n/sub w/ > 3, reaches a maximum in the n/sub w/ region 7-10, and decreases at still higher n/sub w/ values. At the highest n/sub w/, α/sub NaR/ approx. = α/sub KR/ > α/sub w/ and α/sub CsR/ greater than or equal to α/sub w/. The primary hydration numbers of the cations in the resin phase, identified as the n/sub w/ where α starts increasing, are the following: Na+, 3; K+, approx. 2.5; and Cs+, < 2.0. These hydration numbers are comparable to those obtained from dielectric permitivity measurements. It has been concluded that these hydration numbers give the number of nearest-neighbor water molecules which are strongly oriented and participate in hydrogen bonding with water molecules in the next layer. The sequence of α values gives the strength of these hydrogen bonds. 21 references, 1 figure, 3 tables