Dissolution Process of Sodium Chloride Crystal in Water

Abstract

A molecular dynamics simulation has been employed in order to observe the disso- lution process of an NaCl crystal in water at 25 °C. The Tosi-Fumi, Popkie-Kistenmacher-Clementi and Matsuoka-Clementi-Yoshimine potentials have been used to describe ion-ion, ion-water and water-water interactions, respectively. The side length of a box assumed was 2000 pm, in which 216 water molecules, 32 Na + and 32 Cl - ions were contained. The length of the edge of the cubic NaCl crystal having the (100) and the corresponding faces was 1120 pm. The process of dissolution of ions in the crystal was followed over the period of 7 ps from the beginning of the dissolution. It was observed that a chloride ion at a corner of the crystal first dissolved in water. Then another chloride ion at a different corner left the crystal surface. The third and fourth ions dissolving were also chloride ions at the other corners. The velocity of ions leaving from the crystal was estimated from the displacement of the ions with time. For the first chloride ion, this velocity was about 4 x 10 2 ms -1. The velocity of other chloride ions was less than that of the first one owing to electrostatic interactions between a leaving chloride ion and the crystal skeleton becoming successively positively charged. © 1988 IUPAC