Gold – Au

By Monday, December 28, 2015 , , 0

Christmas is coming and if, as a chemist, I had to select an element that reminds me most of this holiday I would select Gold.

Why Gold? Well, the three wise men bought the baby Jesus gifts of Gold (as well as Frankincense and Myrrh). And that is my (weak) link in to this month’s article on the element Gold (!)

Out of all the elements, Gold is perhaps the one that we are most aware of. It is so unreactive that we find it in the ground in its unreacted, elemental state. There are not many elements out there that can claim this.

This however is strange – why do we find it at all? The element is extremely dense. Any Gold present on the Earth when it was forming from a molten lump of rock many billions of years ago should have sunk to the centre. We should not be able to find it at all. One of the theories that is used to explain this is that Gold was added to the Earth when it was bombarded by meteorites (in the ‘heavy bombardment’) after it had formed and solidified. Where did these meteorites come from? Well, your guess is as good as mine!

One of the strange properties of gold is that it can be hammered into layers a couple of hundred of atoms deep – to make Gold leaf. The Gold leaf can then be used to decorate things, making them shiny for literally hundreds of years.

We tend to think of it as being unreactive but it does react (very slowly) with halogens – it also found dissolved in water. But please don’t worry, if you wear your gold earrings in the shower they are not going to disappear down the plug hole!

I’m not even sure if dissolved is the correct word to use – the Gold certainly does not react with the water but it is found in sea water.

And get this – it is estimated that there are 20 million tonnes of it in all of the Earth’s oceans – that means the Gold would be worth around $350 billion (!) – if I have got my calculation’s correct ($35 per gram).

However, don’t rush out to evaporate some sea water to make your fortune, it is found at a concentration of 6 parts per trillion (or 1mg per m3).

So if 1g of gold is worth $35, you’d have to evaporate 1000m3 of water (imagine a swimming pool 2m x 10m x 50m) to get 1g. It would cost you far more than $35 to do this!

Food for thought all the same – have a great Christmas and New Year and I’ll see you in January 2016!

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