Raman Spectroscopy of the Reaction of Sodium Chloride with Nitric Acid:  Sodium Nitrate Growth and Effect of Water Exposure

The reaction of powdered NaCl with HNO 3 was studied using Raman spectroscopy. NaNO 3 growth was monitored as a function of HNO 3 exposure in a flow cell. Mode-specific changes in the NO 3 - vibrational mode intensities with HNO 3 exposure suggest a rearrangement of the NaNO 3 film with coverage. In the absence of H 2 O, intensities of NaNO 3 bands increase with HNO 3 exposure until a capping layer of NaNO 3 forms. The capping layer prevents subsequent HNO 3 from reacting with the underlying NaCl. H 2 O exposure of NaNO 3 -capped NaCl results in hydration of the surface to form an aqueous solution containing NaNO 3 and NaCl. Further exposure results in the formation of a thicker surface-adsorbed H 2 O layer that is consistent with an aqueous NaNO 3 and NaCl solution. Upon exposure of hydrated NaCl to HNO 3, molecular HNO 3 and solid-state NaNO 3 are observed in the thin H 2 O film.