The H2O-D2O solvent isotope effects on the molar volumes of alkali-chloride solutions at T=(288.15,298.15,and 308.15) K

摘要

Densities of LiCl,NaCl,K.C1,and CsCl in normal and heavy water solutions have been measured using a vibrating-tube densitometer with (1-2) o 10~(-6) precision at T- (288.15,298.15,and 308.15) K over a wide concentration range from (0.1 to 5) molal,m.Solvent isotope effects (IE) on apparent molar volumes,as well as both on solute-and solvent-partial molar volumes were evaluated to establish their trend with cationic size in a systematic way.With the exception of the LiCl,both the "normal" standard IEs,(V_2~(deg)(H) > V_2~(deg)(D)),and the "inverse" excess IEs of the solutes,(V_2~(ex)(D) > V_2~(ex)(H)),increase linearly with the electrostriction effect of the cations (l/r_(ion)),while with increasing temperature and/or concentration,the excess effects become almost the same.In contrast to the solute excess IEs,which show linear m-dependence over the whole concentration range,except for LiCl,the "inverse" excess IEs of the solvent,(V_1~(ex) (D) > V_1~(ex)(H)),hardly change over the lower concentration range (DELTA V_1~(ex) approx=DELTA_1~(deg),m <=1).However,with further increase of the concentration,these IEs significantly decrease.Individual ionic standard and excess volume contributions are derived and the results are discussed in terms of structural concepts of ionic hydration.