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Simulation of Monovalent and Bivalent Salts : Does a Computer Model Distinguish Soluble and Non-Soluble Salts?

posted May 11, 2015, 2:07 PM by Shivam Suleria   [ updated Nov 17, 2015, 12:38 PM by Emilio Gallicchio ]
By Shivam Suleria
Undergraduate student at Brooklyn College of CUNY

The aim of the research was to find out that whether a computer model, the DESMOND MD software in the Maestro program (Schrodinger, inc.), is able to distinguish between small samples of crystals of soluble and non-soluble salts. According to hypothesis, the software should distinguish between various monovalent and bivalent salts. Small crystals of Sodium Chloride (cubic crystal structure, monovalent) and Calcium Carbonate (trigonal rhombohedral, bivalent) were selected. Proper structures were constructed using data from crystallographic databases.

First, a typical 64 atom crystal of NaCl was taken in a cubic box of dimension 22 Angstroms. The salt was then hydrated. The molarity obtained after adding the water was 9.979M. The expectations were that the salt will dissolve quickly. Several simulations of 1.2ns, 3.0ns and 6.0ns were done. The results showed that the NaCl crystal dissolves quickly in water (in around 5.0ns). Hence the software correctly predicts dissolution of the crystal into solvated ions (Na+ and Cl-). This is what was expected.

Later on, a small 54 atoms crystal of Calcium carbonate was taken in a cubic box with 20.5 Angstrom sides. Water was then added to it to obtain a molarity  of 10.407M. The expected result was that small crystal will not dissolve at all. Molecular simulation for 50.0ns was ran. Results showed that even after 50.0ns the atoms present in the sample remained together. Hence the assumption was correct. The salt did not get dissolved. Hence it is an evidence that the software, Schrodinger Maestro, is able to distinguish between various salts. The results supported the hypothesis.

Molecular Dynamics Simulation of NaCl

Sodium chloride dissolves rapidly in water (6 ns)

Molecular Dynamics Simulation of CaCO3

Calcium carbonate does not dissolve within 50 ns of simulation.

This was part of an undergraduate honor project for the General chemistry II class of Spring 2015 at Brooklyn College.