Reaction of Nitrogen Monoxide with Oxygen to form Nitric Acid
A flask containing dissolved bromphenol blue indicator is filled with nitrogen monoxide, a colorless gas. When the stopper is loosened, air diffuses into the flask and oxygen reacts with the nitrogen monoxide to form nitrogen dioxide, a brown gas. The nitrogen dioxide dissolves in the solution, creating a partial vacuum within the flask. The resulting pressure difference draws more oxygen into the flask when the stopper is loosened, forming more NO2. Upon dissolving, the nitrogen dioxide reacts with water to form nitric acid, as indicated by the color change of the solution. As more brown nitrogen dioxide forms, more of the gas dissolves, increasing the acidity of the solution.
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