Researcher finds that on water's surface, nitric acid is not so tough

August 20, 2007

Nitric acid is a notoriously strong and chemically destructive compound found in water on earth and in our atmosphere. However, a team of researchers have found that its punch is much weaker when it sits on the top of a water surface.

The discovery of the weaker and more highly exposed nature of nitric acid on the surface of water requires us to re-evaluate how we think about its reactive role in our world, said Geraldine Richmond, the Richard M. and Patricia H. Noyes Professor of Chemistry at the University of Oregon.

Richmond, who was named a Guggenheim Fellow for 2007 earlier this year, described her lab’s exploratory research involving chemical reactions at the surface of water in a talk today at the 234th national meeting of the American Chemical Society in Boston. Her address was one of six scheduled talks on “Recent Advances in Studies of Molecular Processes at Interfaces.”

Richmond is the principal investigator on this and many recent papers that examine unique properties of water surfaces using a combination of computer modeling and laser based experiments.

Nitric acid, a commonly used strong acid in the laboratory, is most notable for its widespread use in the manufacture of fertilizers and explosives. In our environment it is an important player in the atmosphere, where it concentrates in clouds and is one of the primary components of acid rain. Once dissolved in water, its reactive acidic and oxidizing properties can become unleashed. The water causes it to break apart into hydrogen and nitrate ions, creating a highly acidic solution – hence its designation as a “strong acid” – that is very reactive to plants, soils and other matter. At high acid concentrations it can react explosively with other compounds, often releasing highly toxic gases.

Richmond and colleagues have found that when nitric acid swims to the top of a water surface, it tends to tread water – with part of its molecular structure in the air and the rest surrounded by water. Under these conditions they find that it is much less likely to dissociate into its ionic parts – giving the surface of nitric acid solutions very different reactive properties than its well-known reactive and acidic behavior in the bulk of the acid solution.

“Our combined laser experiments and computer simulations provide a rich picture of how nitric acid behaves on a water surface, the way it dances around on the top layer of the water surface in a way that significantly reduces its ability to shed its acidic hydrogen compared to when it is submerged in the liquid,” Richmond said. “Hydrogen bonding to surface solvating water molecules plays a key role in this altered molecular behavior.”

The exposed nature of nitric acid at the surface, Richmond said, makes it more readily available for reaction with immediate surroundings. But as a consequence of this exposure, it acts as a much weaker acid. The results have important implications for understanding the role of nitric acid in our environment, particularly in the many instances where the chemistry in our atmosphere occurs on the surface of nitric acid containing droplets and particulates.

Source: University of Oregon

Explore further: National challenge of leaking mines dwarfs Colorado spill

Related Stories

National challenge of leaking mines dwarfs Colorado spill

August 14, 2015

It will take many years and many millions of dollars simply to manage and not even remove the toxic wastewater from an abandoned mine that unleashed a 100-mile-long torrent of heavy metals into Western rivers and has likely ...

Nano-style sheets may aid health, shield ecosystem

August 13, 2015

Microscopically, "nanomembrane" sheets made from nylon resemble a tangled web. The tiny iron oxide particles on the fiber surfaces can help clean toxic chemicals from water, but if the particles get separated from the web, ...

Droplets levitate on a cushion of blue light

August 11, 2015

Researchers in France have discovered a new way to levitate liquid droplets, which surprisingly also creates a mini light show, with the droplet sparking as it floats above a faint blue glowing gap.

Recommended for you

Interactive tool lifts veil on the cost of nuclear energy

August 24, 2015

Despite the ever-changing landscape of energy economics, subject to the influence of new technologies and geopolitics, a new tool promises to root discussions about the cost of nuclear energy in hard evidence rather than ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.