This is so-called 'artificial snow', or sodium polyacrylate

It's a white powder. If I put a little bit on the desk...

And what happens with this and why people like it: is that it absorbs water very easily.

I've got some water here. And since it's just water, I can do the experiments in my office.

So, are you ready? We'll try and see what happens.

If you pour a bit of water on this

You can see, it swells up

Probably I didn't put enough

Bit more...

It feels very like snow. I can even dribble it on my 'DNA' Christmas tree, that I was given as a Christmas present

Perhaps we should try the experiment on a larger scale

I've got a beaker here and we'll put the lot in

This material is famous for its absorption of water

So if we put in some water here

You can see it really swells up.

If we stir it up, it then starts expanding even more.

The reason why this stuff works is because it's a sodium salt

It is so-called 'acrylic acid', which is a small molecule

which has been polymerised. So you've joined a whole series of acrylic acid molecules together

to form a chain

Because it's an acid, it can be reacted with sodium to make the sodium salt.

The chains, because of the way the polymer is made, are actually linked together so they can't easily separate

So, when you add water, just like to many other sodium salts, it absorbs water

and the sodium ion (Na+) gets water going round it, to hydrate it - gives out energy

If it was sodium chloride the crystal structure would just collapse and it would all dissolve

But because these organic chains are joined together and interlinked, they can't dissolve.

The powder, each grain, is almost like a large molecule. And so, it just swells up

And this has all sorts of practical applications. It's used particularly in babies' nappies

or as you would say in the United States: 'diapers'

where you want to absorb the liquid and keep the baby dry. So you put some of this material inside a pad,

and so the liquid goes through the pad, and swells up, and the baby stays dry. You can use it for other

absorbent materials as well. But it's a very simple material and it's fun to use at Christmas.

So let's make it snow a bit more

Let it snow

200 millimetres of water. We'll try a new, fresh container. This one may be better because all being well

it won't be able to block the beaker in the way. So it's snowing quite nicely

Makes a terrible mess.

(Brady) Who's gonna clean that up?

Me

Everybody else has finished for Christmas. So can't even rely on Neil to clean it up this time

So, happy Christmas! To all of our viewers! And look forward to some really exciting videos for 2015

And a happy new year to you all, and enjoy your chemistry