Salt Simulations
(1) Large Salt Crystal in Water (Water Shown)
This is a simulation of a single, large salt crystal (Na+,
blue; Cl–, green) in water (red and
white sticks). altogether there are 512 ions (256 sodium and 256
chloride) in an amount of water to give a salt concentration of 1.1
M. Initially, the crystal has a cubic shape, and over the
course of 2 nanoseconds, very few of the ions can been seen to
dissociate from the parent crystal and become
solvated.
The slight separation of positive and negative charges within the water molecule
cause the water molecules to orient with respect to the ions. The result is
that sodium ions tend to be surrounded by water oxygens and chloride
ions by water hydrogens.
(2) Large Salt Crystal in Water (Water Hidden)
This is the same simulation as shown in (1) above, but water has been hidden from view.
(3) Small Salt Crystals in Water (Water Shown)
This is a simulation of eight small salt crystals (Na+,
blue; Cl–, green) in water (red and
white sticks). (In fact, we have simply broken up the single
large crystal shown before into eight smaller crystals.) Initially,
the crystals all have a cubic shape, and over the course of 2
nanoseconds, they become completely dissolved in the water.
The simulations of large and small salt crystals together demonstrate
that the state of subdivision of matter can play a role in the rate
of a reaction. In this case, the reaction is not a chemical
reaction per se, but a physical process known as
solvation.
(4) Small Salt Crystals in Water (Water Hidden)
This is the same simulation as shown in (3) above, but water has been hidden from view.
(5) Small Salt Crystals in Oil
This is a simulation of eight small salt crystals (Na+,
blue; Cl–, green) in oil
(grey). Specifically, the oil is composed of the alkane
molecule octane,
one of the principal components of gasoline.
Initially, the crystals all have a cubic shape, and over the course of
2 nanoseconds, they remain largely intact.
The simulations of the small crystals in water versus oil pertain to
the solubility
of a substance. The rate at which a compound dissolves
in solvent can depend on a number of factors, including the chemical
composition of the solute and solvent, temperature, agitation, and
state of subdivision of the solute.