Kitchen chemistry: a new post series

I’m beginning a new educational post series on chemistry in the kitchen. The kitchen tag will find them all.

The kitchen, of course, is a wonderful place to observe the states of matter and the transitions between them. Solid ice melts (as in the time-lapse animation below), giving liquid water. Liquid water boils, giving water vapour (a gas). Water vapour condenses, giving liquid water again.

Colloids and suspensions are also common in or around the kitchen. Mist is an example of a liquid aerosol (fine droplets of a liquid in a gas such as air). Step outside the kitchen, and clouds are an example of a solid aerosol (fine particles of a solid – ice, in this case – in a gas such as air). Dust is another example of a solid aerosol.

Whipped cream is an example of a foam (fine bubbles of a gas, such as air, in a liquid). Many recipes call for foams of one kind or another. Milk and mayonnaise are examples of emulsions (fine droplets of a liquid, such as oil, in another liquid, such as water). An additional substance (an emulsifier) must normally be present to stop the dispersed droplets from joining up together (thereby forming a layer of oil on top of the water). Paint is an example of a sol (fine particles of a solid in a liquid). A sol must be distinguished from a solution, where the solid is totally dissolved in a liquid, and no solid particles exist.

Meringue is an example of a solid foam (fine bubbles of a gas, such as air, in a solid). Solid foams usually result from hardening a liquid foam in some way (in this case, by baking). Jelly is an example of a gel (liquid dispersed in a matrix made from a solid – gelatine, in this case). Finally, ruby glass (also known as cranberry glass) is an example of a solid sol (fine particles of a solid in another solid). In the case of ruby glass, very tiny gold particles give the glass a rich red colour.

See here for the next post in the series.

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