Water
Water, a simple yet under-appreciated substance, is essential for life. It plays a key role the biological processes that occur in the human body as well as the process that plants use to convert sunlight into energy.
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If you look at Earth from space, its defining feature is water. Our planet is blue with the stuff. A deceptively simple compound, water is composed of two atoms of hydrogen to one of oxygen – making it technically dihydrogen monoxide or oxygen hydride, though these are terms only likely to be used to emphasize geeky credentials.
It would be meaningless to speak of a discoverer of water – we’ve always been aware of it – but various scientists lay claim to uncovering water’s composition. Laviosier realised that hydrogen and oxygen could be made from water in the 1770s, but the explicit discovery of its makeup is down to either James Watt, who suggested its composition in 1783, or Henry Cavendish who recombined oxygen and hydrogen in 1781, but didn’t publicise it until a year after Watt’s discovery. We do know, though, that it was in 1826 that Jöns Jakob Berzelius fixed the atomic weights of hydrogen and oxygen, and came up with the familiar H2O designation.
Over 70 per cent of the Earth’s surface is water - in round figures there are 1.4 billion cubic kilometres. This is such a huge amount, it’s difficult to visualise. A single cubic kilometre is a trillion kgs of water. That’s a nice round number because water had a starring role in the establishment of metric units. A gram was originally defined as the weight of a cubic centimetre of water.
Water has huge significance for biology, so much so that the when we search the solar system for likely signs for life, we first look for water. Bacterial life has been found at the extremes of heat, cold and airlessness that our planet can serve up. There is no known life without water.
Underlying water’s importance is a unique collection of properties. It’s the only compound that exists as solid, liquid and gas at the typical temperatures of the Earth’s surface. And as a molecule it has some surprising characteristics – without one of these, its boiling point would be below -70 degrees Celsius. There would be no liquid water on Earth, which means no life. But thanks to this special property the water molecule shares with a few others, it boils at the familiar 100 Celsius.
Visit Chemistry World for more about water, the compound that brings us to life.
Excerpted with permission, www.rsc.org/chemistryworld.