Ion hydration in aqueous CaCl₂solutions

Abstract

The neutron first-order difference method has been applied to a 4.49 molal aqueous solution of CaCl 2 . Isotopic changes were made in both the Ca 2+ ion and the Cl - ion so that a complete picture of ionic hydration could be obtained. Both ions coordinate water in a non-dipolar configuration with ion-oxygen distances close to those predicted by gas-phase quantum molecular calculations. The measured hydration numbers for cations and anions (5.5+or-0.3 and 5.8+or-0.3 respectively) imply substantial sharing of water molecules between the ions.