Hydrate Chemistry

As I've previously indicated on this blog, I am primarily an AQUEOUS inorganic chemist. As such, I've prepared a wide variety of aquated metal complexes over the years, but I've never paid much attention to solid hydrate chemistry. And that's a shame, since there is a lot of good chemistry in that area, some of which I'm dealing with right now.

A few months ago, we decorated our ceilings with crown molding. Unfortunately, the original builders of our house placed the water pipes too close to the ceiling, which meant that two months after the crown molding was added, the FOUR nails which had punctured the pipes rusted and caused the pipes to leak. The resulting repair left a hole in the ceiling which was my job to fix. The material of choice for this type of repair is drywall (sometimes called sheetrock). Drywall is prepared by mixing CaSO4 · 1/2H2O with water to form CaSO4 · 2H2O, a hydrate with enough strength to be used to construct walls. Considering the fact that the added water forms no bonds other than hydrogen bonds, it's a little surprising that the resulting hydrate is so stable.

Of course, the strength of CaSO4 · 2H2O is nothing compared to that of another well-known hydrate. Cement begins as a mixture of CaO and SiO2 in various proportions, which is then reacted with water to form a calcium silicate hydrate.

2 Ca3SiO5 + 7 H2O —> 3 CaO · 2 SiO2 · 4 H2O +3 Ca(OH)2

Actually there is an entire series of hydration reactions which occur during the hardening of cement, with reaction times ranging from hours to weeks. Again, the strength generated by the formation of a hydrate is simply amazing.

Another hydrate with interesting chemistry is methane hydrate. Containing 5-6 molecules of water for every molecule of methane, this material can be found in huge quantities along the ocean floor. Wiki link here. It has been described as both a huge, untapped energy reserve and a major source of greenhouse gas. The latter description has become more significant as the temperature of the oceans continues to rise, since methane hydrate is only stable at low temperatures. It's also been used to explain the disappearance of ships in the Bermuda Triangle. What more could you ask from a simple compound?

Anyway, the ceiling is fixed.