Title

Dilution of a solution could produce even more pollution

Presenter Information

Daniel Barry

Presentation Type

Presentation

Abstract

“Dilution is the solution to pollution” is a familiar catch-phrase, but it might not always be the case. This project describes a situation in which the concentration of metal ions in a solution increases as the system is successively diluted. Termed “anti-buffering”, it is a consequence of metal complexes possessing a stoichiometry higher than 1:1. Under conditions for which the complexing ligand is in excess, the dissociation that accompanies dilution will release metal ions in amounts that are significant compared to what was there before. While the level of metal ions increases, the levels of complexed metal and free ligands diminish with dilution. The extent of anti-buffering conditions can be shown by means of a composition grid. The analytical concentration of metal is plotted on the x-axis of the grid and the analytical concentration of ligand is on the y-axis. The z-axis then records the equilibrium activity of metal ion. Anti-buffering has been demonstrated in the laboratory using a 10:1 ethylenediamine / Cu2+ mixture in a sealed reaction chamber. The system was successively diluted under an inert N2 atmosphere at constant pH and temperature. In one case, the free metal activity increased two orders of magnitude while the system underwent a 26-fold dilution – a result 2600 times larger than might ordinarily be expected in such a scenario. Conditions similar to the experimental setting could occur in the environment as water from a tributary stream enters a larger body of water. This could lead to increased bioavailability of toxic heavy metals.

Category

Physical Sciences

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Apr 13th, 9:20 AM Apr 13th, 9:40 AM

Dilution of a solution could produce even more pollution

UC 331

“Dilution is the solution to pollution” is a familiar catch-phrase, but it might not always be the case. This project describes a situation in which the concentration of metal ions in a solution increases as the system is successively diluted. Termed “anti-buffering”, it is a consequence of metal complexes possessing a stoichiometry higher than 1:1. Under conditions for which the complexing ligand is in excess, the dissociation that accompanies dilution will release metal ions in amounts that are significant compared to what was there before. While the level of metal ions increases, the levels of complexed metal and free ligands diminish with dilution. The extent of anti-buffering conditions can be shown by means of a composition grid. The analytical concentration of metal is plotted on the x-axis of the grid and the analytical concentration of ligand is on the y-axis. The z-axis then records the equilibrium activity of metal ion. Anti-buffering has been demonstrated in the laboratory using a 10:1 ethylenediamine / Cu2+ mixture in a sealed reaction chamber. The system was successively diluted under an inert N2 atmosphere at constant pH and temperature. In one case, the free metal activity increased two orders of magnitude while the system underwent a 26-fold dilution – a result 2600 times larger than might ordinarily be expected in such a scenario. Conditions similar to the experimental setting could occur in the environment as water from a tributary stream enters a larger body of water. This could lead to increased bioavailability of toxic heavy metals.