Gas Clathrate Hydrates Experiment for High School Projects and Undergraduate Laboratories

We present a laboratory procedure, suitable for high school and undergraduate students, for preparing and studying propane clathrate hydrate. Because of their gas storage potential and large natural deposits, gas clathrate hydrates may have economic importance both as an energy source and a transportation medium. Similar to pure ice, the gas hydrate structure consists of a lattice of water molecules held together by hydrogen bonds. However, the gas hydrate lattice is more complex than that of ice: "host" cages are formed in which the "guest" molecules are trapped. Despite the fact that the gas hydrate lattice is less stable than the ice lattice, the van der Waals forces between the guest molecules and the host lattice stabilizes the overall structure. Propane clathrate hydrate is an especially interesting example because the solid is a mixture of two chemicals that are immiscible in the liquid state yet it has a higher melting point than that of pure water ice. A simple procedure is outlined for students to synthesize and study propane hydrate. This experiment introduces students to this unusual solid, while stimulating a discussion of the interplay of intermolecular forces, thermodynamics, and solid structure.