Hydrates - Up Close and Personal
Certain chemical structures called clathrate hydrates can be found on the bottom of our oceans or built in a lab. Kristen Pallen ’12 says that these structures can form in pipelines, while Lennox Chitsike ’13 explains that hydrates have the potential to act as a reservoir of molecules of economic importance such as fluoride ions and methane. However, scientists still do not know much about these recently-discovered crystalline solid. This summer seven students are working with Assistant Professor of Chemistry Camille Jones to conduct research related to hydrates, including examinations of different hydrate properties.
Clathrate hydrates are composed of a network of hydrogen-bonded water molecules around a guest molecule. These guest molecules are trapped within the structures and hydrates work as an effective “cage” to keep them contained. The students are working with several guest molecules and salts to test for a range of thermodynamic and physical properties, as well as a variety of other projects. Their research promises to unlock new information about these structures.
Chitsike will explore the effect of salts on hydrates with the guest molecule THF for his project. He has worked hydrates containing the guest molecule trimethylene oxide (TMO) over the previous summer using cooler baths and has come to the conclusion that sodium fluoride salt stabilizes these hydrates. When salt is added to a clathrate hydrate, the hydrate is referred to as “doped.” His current task is to support his previous findings using other salts for comparison, including potassium fluoride, potassium chloride and sodium chloride. Chitsike’s goal is to see if they have the same potential to stabilize THF hydrates. He is looking at properties including enthalpy of dissociation and melting point using a differential scanning calorimetry instrument (DSC). Chitisike hopes to replicate his previous results of higher stability in doped hydrates by observing higher melting points.
Pallen is working on an NMR study of THF clathrate hydrates. This marks Pallen’s third summer working on this project, and she has enjoyed watching it progress. Though she has worked with sodium fluoride and potassium fluoride doped hydrates before, her studies have focused on changes in melting point as a measure of stability. Now, Pallen’s project aims to discover more about how the doped hydrates look on a molecular level. To do this she must send her samples to Florida, where the samples can be analyzed with a fluorine NMR, ( nuclear magnetic resonance) instrument. Using the spectra obtained from fluorine NMR analysis, Pallen will be able to piece together fluorine’s place in the hydrate structure. In the meantime, she is using computer software to create 3-D models of what the hydrate structures may look like, which will be beneficial after she obtains the NMR spectra.
Tenzing Lama ’13 and Deric Mei ’13 are working with TMO and cyclopentane hydrates, respectively. They are trying to find an efficient way to create the hydrates and testing some of their properties after they have been doped with salts. They're looking specifically at the effect of salts on the volume of the hydrates. To accurately test their samples, they’re sending the samples to Syracuse, where they will be evaluated using X-ray powder diffraction, which shows the crystallographic characteristics of the sample. These characteristics can help determine the structure, dynamics, and volume when combined with the technique of Rietveld refinement. To create the hydrates, Mei and Lama must freeze and thaw a solution of water and their respective guest molecules until the structure is complete.
Pauline Wafula ’13 is also working with hydrates and salts, though with different guest molecules. She hopes that when salts penetrate a hydrate structure, they work to reinforce it. However, Wafula has found that when she uses sodium fluoride and potassium fluoride, the salts dissociate, or separate into ions, in solution and the resulting fluoride ion pulls a hydrogen atom off a water molecule, displacing a hydroxyl ion from the structure. Ironically, hydroxyl ions in solution actually serve to weaken the overall structure, creating “holes” rather than providing strength. The hydroxyl ions cause the solution to be alkaline, and so to neutralize the solution; Wafula is attempting to add acid to her hydrate solution. By adding hydrofluoric acid, a weak acid, she hopes to see the pH of the solution return to a neutral level of 7, so that the solution can act as if it were water.
Elizabeth Costello ’13 is working on a melting point study to see if ammonium fluoride stabilizes semi-clathrates composed of water and THF as the guest molecule. Semi-clathrates are hydrates that include molecules other than water in the cage-like part of the structure. Costello is also helping Professor Jones set up a website and write an article for the Journal of Chemical Education about a solid state chemistry class. Both the website and the article will describe how to teach a course about the crystal structure of chloride and oxides of alkaline earth metals and alkali metals. Specifically, Costello is looking at the similarities between alkaline earth oxides and alkali chlorides and examining trends in the structures and properties of these compounds.
Joshua Snyder ’13 is studying the decomposition of metal carbonates, some of which can be studied in hydrate form. A metal carbonate is composed of any metal and a carbonate group. The compound decomposes to form a metal oxide and carbon dioxide. Snyder is looking at periodic trends to explain the relationship between the decomposition rates of different metal carbonates. When in a salt state hydrate form, metal carbonates can stay in a solid state for longer periods of time. Snyder is looking at the melting points of different metal carbonate hydrates to see which of these hydrates is the most stable. He’s also examining the reaction of magnesium burning in dry ice without oxygen, and he is trying to find the products of that reaction.
Lama’s, Pallen’s and Chitsike’s summer research was funded through the Edward and Virginia Taylor Fund for Student/Faculty Research in Chemistry, established in 2008 through a gift from Ted ’46 and Virginia Taylor to inspire students interested in chemical research and to facilitate their work with outstanding faculty.
Clathrate hydrates are a relatively new area of study, and some researchers believe that these structures can hold important implications in both chemistry and economics. However hydrates might be useful, it is critical to study their structures and properties as well as investigate methods of stabilizing them. Professor Jones’ research group hopes to uncover more about these structures and contribute to a growing body of science about hydrates.