Science in little things #2 – Dish washing

Unless you are monstrously rich or incredibly lucky (or both) you have to do the washing up, right? Quite a boring task, that includes drenching your cuffs, geting dry hands and dealing with filthy objects.  Personally, doing the dishes is not the housework I hate the most (the one I really can’t stand is dusting), but I can’t help thinking about how much worse it could be without chemistry.

Why? Well, think about that unbelievably dirty oven pan. Oh, yes the lasagne you cooked in it was delicious but now washing it without soap only with water and elbow grease is sheer drudgery, isn’t it? Chemistry helps us in this task with surfactants.

Surfactants are surprisingly useful molecules, composed by two parts: a hydrophilic head, that is attracted and tends to be dissolved by water, and a hydrophobic tail, that is repelled from water. Surfactants have a lot of uses; in soaps they are used because of their ability to create micellae. And what is that? Keep calm, I am about to explain.

Micellae are an aggregate of surfactants, that organize themselves in order to form a sort of bubble. In water, the surfactants tend to form a bubble with their hydrophilic heads pointed towards water and their hydrophobic tails pointed towards the inner part of the bubble, as far as possible from water.

Tensioattivi micella

This image is from Wikipedia

Now, since dirt is usualy made of fat substances that are not attracted by water, it tends to be included into these micellae. Trapped inside a layer of surfactants, dirt can be easily removed by mechanical action. Easy like that!

Moreover surfactants have the ability to lower the surface tension between a liquid (in this case water) and a solid (your dishes), enhancing the wetting power of water. This is the same that happens when you have a shower. Have you ever noticed that your body seems to repell water unless you use soap? That’s due to the fact that we are for the most part made of hydrophobic molecules. Surfactants contained in soaps and shampoo help both to wet our bodies and remove dirt.

Remember: chemistry is everywhere! Think about surfactants and micellae next time you do the washing up.

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