Water's choice: A tale of two numbers and the order they predict

October 19, 2010, Pacific Northwest National Laboratory
This work graced the cover September 30, 2010, issue of The Journal of the Physical Chemistry A.

(PhysOrg.com) -- Well-ordered structure or chaotic jumble? That's the choice when water is mixed with a salt and cooled down. Now, thanks to a rule discovered by scientists at Pacific Northwest National Laboratory and the Technical University of Munich, predicting the structure of a frozen mixture of various salts and water is as easy as comparing just two numbers.

The rule, simply put, compares two numbers. The first is the amount of energy that is released when a particular salt is dissolved in water. The second number is the amount of energy it takes to melt ice into regular water. If the first number is smaller than the second, a highly structured hydrate forms. Otherwise, salt and water won't mix together, but will be separated in their ordered forms.

"We tested the rule against 75 different types of salts, which was everything we could find in the literature," said Dr. Sotiris Xantheas, a theoretical chemist at PNNL. "And it correctly predicted the outcome each time, as verified by laser experiments."

This rule provides insights into the behavior of water, the most ubiquitous on the planet. By being able to quickly determine how water arranges itself in ordered environments with different salts, scientists can learn more about the properties of water at the molecular level. This is important to understand its relevance in many chemical and biological processes that are related to energy, and environmental remediation. "This rule really opens up new ideas about how salts form hydrates," said Xantheas.

As in discovering any new rule, the scientists wanted to see if it applied to more than a handful of cases. So, they devised a series of tests in Germany and the United States. The German team mixed various salts with and cooled them to access their ordered structures. Then, they used looking for the "smoking gun" to determine whether the salt formed a hydrate. The calculation of the spectra, performed in the United States, matched the experiment and offered additional insight into the correlation between structure and spectra in those ordered environments. The collaboration started during Xantheas' visit to the Technical University of Munich last summer as part of his Alexander von Humboldt Fellowship.

Xantheas and his collaborators, including Jasper Werhahn, who is coming to PNNL for 3 months under a Max Planck Fellowship to perform calculations, are continuing to study the properties of those ordered aqueous environments.

Explore further: Salt could cool cores of advanced nuclear reactors

More information: Pandelov S, JC Werhahn, BM Pilles, SS Xantheas, and H Iglev. 2010. "An Empirical Correlation between the Enthalpy of Solution of Aqueous Salts and Their Ability to Form Hydrates." The Journal of Physical Chemistry A 114(38):10454-10457. DOI:10.1021/jp106050r

Related Stories

Salt could cool cores of advanced nuclear reactors

November 3, 2006

The water in a conventional nuclear reactor cools the core, but a graduate student at the University of Missouri-Rolla says salt would be a better alternative in some advanced reactor designs.

Hot and cold moves of cyanide and water

September 3, 2009

Scientists have long known that molecules dance about as the temperature rises, but now researchers know the exact steps that water takes with a certain molecule. Results with small, electrically charged cyanide ions and ...

Hot and Cold Moves of Cyanide and Water

September 8, 2009

(PhysOrg.com) -- Scientists have long known that molecules dance about as the temperature rises, but now researchers know the exact steps that water takes with a certain molecule. Results with small, electrically charged ...

Sopping salts could reveal history of water on Mars

October 6, 2004

Epsom-like salts believed to be common on Mars may be a major source of water there, say geologists at Indiana University Bloomington and Los Alamos National Laboratory. In their report in this week's Nature, the scientists ...

Could the Taste of Vodka be Related to Molecular Makeup?

May 28, 2010

(PhysOrg.com) -- When we think of taste, we don't normally think about how something's molecular makeup influences our tongues. A group of scientists at the University of Cincinnati and Moscow State University tested the ...

Recommended for you

Nanoparticle gel controls twisted light with magnetism

January 22, 2018

"Help me, Obi Wan Kenobi. You're my only hope." For many of those around at the release of Star Wars in 1977, that scene was a first introduction to holograms—a real technology that had been around for roughly 15 years.

On the rebound

January 22, 2018

Our bodies have a remarkable ability to heal from broken ankles or dislocated wrists. Now, a new study has shown that some nanoparticles can also "self-heal" after experiencing intense strain, once that strain is removed.


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Oct 19, 2010
Useful in desal process?
not rated yet Oct 19, 2010
Mainly useful for determining the freezing point of aqueous salts, as a performance characteristic.

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.