Crystallography365

Blogging a crystal structure a day in 2014

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Contributed by

Helen Maynard-Casely

It is sitting in your stomach – Hydrochloric acid

What does it look like?

HCL

What is it?

Hydrochloric acid is a very nasty chemical in its concentrated form, but lives within us all as a vital part of our digestion system. Hence, the gratuitous posting of this by the Periodic Video people. 

But you can solidify this acid by cooling it down enough, to a structure where the pairs of Hydrogen and chlorine atoms can rotate around. It's a solid, but a bit of a wobbly one. If you cool it further, lower than -180°C, then this arrangement changes. The pairs of atoms stop moving and the structure becomes the more ordered (form III) structure that we've shown an image of the atomic arrangement.

Where did the structure come from?

The crystal structure of 'form III' of hydrochloric acid was determined in 1967 by Sandor & Farrow and is #9014578 in the Crystallography Open Database.

Tags: acid   molecular   digestive   hydrogen