Boiling point of water

At what temperature does pure water at atmospheric pressure boil? asks James Poskett in this month’s Last Retort column in Chemistry World. The obvious answer is 100 Celsius, but the boiling point of pure water can be as low as 97 Celsius (at atmospheric pressure) and as high as 109 Celsius! And this has nothing to do with colligative properties in which adding a solute, such as salt, to water raises its boiling point and conversely lowers its freezing point.

Poskett points to an intriguing video on the University of Cambridge website that shows the thermometer creep past the 100 degrees mark as distilled water boils in a glass beaker (The yellow highlight in the picture above shows the water boiling at 100.9 Celsius). He discusses the notion of “cold” being something positive, rather than simply the absence of heat. He scoffed at the notion, at first, but it’s a concept well known to chemical engineers and plant designers who talk about “coolth” being the opposite of “warmth”…

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