Condensation…

When water vapour meets the glass of a beaker containing cold water or ice it condenses into a liquid, forming droplets of water on the outside of the glass. If you heat a beaker of water with a Bunsen flame, water vapour produced by the flame initially condenses on the cold surface of the beaker.

The Bunsen burns methane, a very simple hydrocarbon (CH₄) which combusts to become carbon dioxide and water. As the beaker warms up the condensation on the outside evaporates again. The water inside the beaker begins to warm up too. Watching water warm up is surprisingly interesting!

Gases from the atmosphere are slightly soluble in cold water but much less soluble in warmer water. That is why the colder parts of the ocean are so full of food to feed the Earth’s largest mammals. Solubility is measured in g per 100 g of water (at a given temperature and pressure). At room temperature and pressure the solubility of nitrogen is roughly 0.0019 g/100g, oxygen is about 0.0043 g/100g and carbon dioxide is 0.1690 g/100g. This means that any tap water that has been exposed to the atmosphere for any length of time will have some dissolved gases.

The gases become less soluble when the water temperature rises. As water warms up, the gases come out of solution and form tiny bubbles. Fizzy drinks lose their fizz when they become warm. Next time you heat a beaker of water look closely to see the tiny bubbles appearing between 30 & 50 °C. If the water becomes much warmer than that all of the dissolved gases will evaporate and the bubbles disappear. At high temperatures bubbles containing water vapour start to form as the water begins to boil.

I like to cross-pollinate my posts with links to different aspects of science. I made a reference above to the planet’s largest mammals. This made me think of an excellent, short video by George Monbiot about trophic cascade – the idea that top predators have a profoundly important role in managing ecosystems. Research suggests that whales perform a crucial role in controlling the presence of nutrients and dissolved gases in the sea. They are large enough that this contribution is significant – the fact that their numbers are historically low is dangerous not only for them, but also perhaps for us.