What is it about?
All chemists know that liquid water changes significantly upon addition of a strong base - like sodium hydroxide . This happens because the hydroxide ions become surrounded ("solvated") by water molecules, forming aggregates whose structure was intensively debated before our study. Here, we modeled the water-hydroxide liquid solution and validated our results by comparing them with experimental data. This allowed us to propose, for the first time, a consistent molecular-level picture of the structure of the hydroxide-water complexes in acqueous solutions.
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Why is it important?
This was one of the first modeling studies of acqueous solutions based on accurate (but also very time expensive) computational techniques - first-principles molecular dynamics, in the present case. I remember that it took us really a huge lot of time just to run the simulations that we needed to collect the data - actually, around the year 2000, machines weren't as fast as today, of course ;-) Anyway, such an effort was rewarded because we've got quite a few interesting tips on how the most important liquid on earth behaves when a strong base is added. For example, for both the sodium-hydroxide and potassium hydroxide acqueous solutions, we found that the so-familiar tetrahedral coordination geometry of water is completely missing at high concentrations of the hydroxide. This indicates that hydroxide anions have a massive effects on the hydrogen-bond network of water.
Perspectives
Acqueous solution of hydroxide ions are tough systems for both experimental and computational approaches. Notwithstanding the wealth of studies performed to date, the underlying mechanism of proton transfer in acqueous-hydroxide solutions still remains debated. In particular, how the chemical nature of the positive ions (sodium or potassium, for example) can affect this mechanism, is not fully understood yet. I'm glad to see that such an 'old' problem is still interesting and fascinating for other researchers.
Gloria Tabacchi
university of insubria
Read the Original
This page is a summary of: First-Principles Study of Aqueous Hydroxide Solutions, Journal of the American Chemical Society, July 2002, American Chemical Society (ACS),
DOI: 10.1021/ja020350g.
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