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Amedeo Avogadro

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The Avogadro Constant NA is well-known as a fairly large quantity – in some parts of the world it is called Loschmidt’s number, L, after the Austrian chemist who first estimated its value. But how large is it?


About 20 years ago a colleague in my then department rang me; he wanted to get a pile of sand with NA sand grains in it to show to his pupils. I said that if he could find a merchant to supply it then I would guarantee that the school would pay for it. Perhaps he would let me know how much he needed…..

For the sake of this order-of-magnitude calculation let’s assume that each grain is a cube 0.1mm on a side, and that the grains pack perfectly with no spaces. Since it makes the calculation marginally easier, let’s also deal with 1024 grains – this is the same as the number of molecules in 30cm3 or a couple of tablespoonsful of water.

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It is better if you go through the calculation. So we shall do it step by step; click on the Next button to move further through the document.