The purpose of this experiment is to better improve chemical models of reactions that occur at the surfaces of snow and ice by determining the pH changes at the microscopic layer of liquid that forms on ice. Some reactions which occur at the interface of this liquid and the atmosphere alter the composition of the atmosphere and are acid-catalyzed. The change in pH upon freezing was measured by mixing solutions of water and acetic acid which were frozen and monitored by infrared spectroscopy. The temperature was varied between -20 and -6 degrees Celsius and spectra were taken at the different temperatures. The pH was then determined by comparing the ratios of absorbance between the acetic acid and its conjugate base acetate. The experiment was repeated with the addition of sodium chloride (0.5 M) to see if the addition of a solute would change the observed trends. The salt only caused the solution with a room temperature pH equal to the pKa of acetic acid, 4.7 to decrease in acidity upon freezing and return to the room temperature pH as more of the solution became liquid. The added salt did not change the acidity of the solution with a room temperature pH of around 3.7. Solutions were also frozen top-down, as compared to bottom-up freezing that occurred in all other trials. Top-down freezing caused acetic acid solutions to start at a slightly more acidic level and gravitate above the room temperature pH as the temperature increased. Solutions with artificial sea salt were compared to the solutions with sodium chloride.

Determining the pH of frozen and annealed acetic acid and sodium chloride solutions using infrared spectroscopy

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.