Chemistry

Welcome to lecture, what I'm going to do now is begin with an experiment to ilustrate this point, that the oxygeon molecule O2 has unpaired electrons.

Alright just to show you the reactivity of this liquid oxygen. So you can see wonderful liquid oxygen, nice blue colour. Here on the table we have a nice tin tray which we're gonna use to contain an experiment I'm gonna show you next. So we've got our favourite liquid oxygen, there- strongly oxidizing, very very reactive and here I've got some cotton wool.

Oxygen is allotropic element because it exists in two forms. The form which we breathe all the time is O2 (two oxygen atoms joined together) and there's another form: Ozone which has three atoms arranged like letter V.

Oxygen has unpaired electrons within moleculal orbitals around the structure, and these unpaired electrons give the colour and that colour is blue. So blue is often perceived to be the color of solvated or unpaired electrons. Lots of chemists are scared when they see the blue of liquid oxygen. Liquid oxygen is very, very reactive. Generally you only make liquid oxygen by mistake, not like today when we're making some on purpose. And if you made it by mistake in an uncontrolled way where there might be organic molecules, perhaps simple organic chemicals like hidrocarbons, grease, they tend to detonate and they tend to cause very energetic experiments. I am gonna put the cotton into the tin tray.

So we begin with high tech piece of equipment which is a test tube on a piece of string. What we're gonna do is we're gonna put some liquid nitrogen in here, you can see liquid nitrogen- well you may not see it since it's colourless. So this is liquid nitrogen, and what i hope you can see is that these magnets which are pretty good magnet has absolutely no effect at all on a liquid nitrogen. I can pull the magnet and nothing happens.

And then we're gonna fill up all of the void space between the cotton particles with oxygen so you might wanna stand back after this. Here we go, here's our liquid oxygen. Do you wanna come in and zoom in? So here you can see all the lovely blue liquid oxygen going into cotton wool particles.

lets try the same thing with liquid oxygen. Careful with my shoes!

So here we have a match on a stick, and i think you can see it's probably light. We have our fire, our oxygen, and we have our fuel and let's see what happens when we put it all together.

The liquid oxygen has a very nice blue colour today. So let's try, here's the magnet again. And if i take liquid oxygen, you see i can pull it up right here. It's not as magnetic as my keys but you can see there's really big difference- it sticks to the magnet. So you can see it really is magnetic.

You ready? Okay.. Wohoo and there she blows! Hihi

And ozone is much more reactive than oxygen so near the earth surface where we are at the moment, ozone is really quite dangerous because if you bring the tin it can start reacting with any sort of moleculs which has bonds between carbon. But in the upper atmosphere, ozone is extremely important because it absorbs ultraviolet light that comes from the sun and stops this ultraviolet light attacking the moleculs and biological species on the surface. If it wasn't for the ozone in the upper atmosphere, all of us would be- if not dead, certainly very much less comfortable than we are at the moment.

So neil's now connecting up a piece of tube to the oxygen cyllinder and he's gonna fill up this gas jar with oxygen. and we're gonna do a really classic experiment, the one that everyone knows at school as test of oxygen, is to relight a glowing splint. so we have a traditional gas jar full of oxygen, so here you can see we're burning a splint. so this is the wood burning excess oxygen around us. so what now we're gonna do is we're gonna take the splint out so that it's just glowing. if you blow on the splint you see it gets brighter. now we're gonna try to relight that splint by putting it into very oxygen rich atmosphere so we'll move over to the jar and put in our glowing splint. and you can see the flame come backs to life. so that's a test that everyone learns for oxygen rich environment. What happened, what made that happen? Well the increased oxygen content concetration reignites, reinitiates that oxydation of the wood, the burning of the wood.