Benzene - Periodic Table of Videos

so this is benzene it's an organic compound so it's a ring of six carbons with hydrogens coming off each carbon benzene is a very interesting molecule its structure has six carbon atoms each with one hydrogen atom attached to it it's used as a solvent benzene actually quite carcinogenic we found out now that actually causes cancer it's pretty toxic so so we have to treat it with the utmost respect the stretch mystified chemists how could you have six carbons and six hydrogen's all in one molecule when Benjamin discovers people didn't actually know what the structure it was they knew it had six carbons and six hydrogens they didn't actually know what sort of form it took and basically it was down to somebody called kaki lay who proposed the structure of benzene and apparently the structure of benzene came from a dream he had where he dreamt of a snake eating its own tail he dreamt there's a snake was biting its own tail and he developed the idea that benzene was a ring apparently so he says afterwards but the actual structure wasn't worked out until the 1930s when crystallography showed that it really was a flat molecule and the chemist named Kathryn Lonsdale who was the first woman ever to be made a fellow of the Royal Society the bridge UK Academy of Sciences she worked out the structure of benzene the structure of benzene is a hexagon of carbons a hydrogen comes off of each carbon what we have is a double bond double bond double bond so we have a double bond single bond double bond single bond double bond single bond so the way chemists often draw benzene is a suit is a hexagon with a ring in the middle to show that the electrons are delocalized as we call it so over each carbon the delocalized over each carbon and benzene is an aromatic compound we call aromatic compounds compounds that have these sorts of structures Michael Faraday made a sample of benzene early in the 19th century and in about 1980 a bottle was found labeled Faraday's benzene and the British company BP who wonderful and analytical labs analyzed benzene faraday's benzene and it came out to be purer than modern benzene when you buy really high purity benzene so everybody was a bit suspicious was this Rayleigh Faraday's benzene but it had 37 trace impurities tiny impurities that and which they also saw and then another bottle of Faraday's benzene was found in a different lab in London and it was analyzed and it had exactly the same impurities it was found out that the reason that Faraday's benzene was so pure is that benzene freezes at quite a high temperature goes solid at about 6 degrees centigrade and Faraday used crystallization rather than the modern way of purifying it which is distillation which is much better on a large scale but doesn't give you quite such a high purity product and bending has an unusually high melting point so it becomes solids at five point five degrees so hopefully when I put it some ice and see if we can get it to go solid benzene has been found moderately recently in the last 40 years or so to be toxic it's not an acute poison it doesn't make you drop dead immediately but it can promote certain cancers particularly leukemia so when I was at school people use benzene quite freely but nowadays we wouldn't let school children or even students use it except them special precautions I found here this is my school LED book which I did experiments about 46 47 years ago it's got some quite nice pictures in it and here there's an experiment which I did preparation of nitrobenzene this is reacting benzene with sulfuric acid and nitric acid and I used 50 milliliters of benzene that's really quite a large amount nearly two ounces of benzene and nowadays this would not be allowed at all at school so we're in our few can cover so what we have here is just mice put a lot bit of water in it hopefully get a nice nice contact between the test tube and the ice this is just a normal test tube what I'm going to try and do is put some of the benzene in the test tube I'm going to have to leave it for a little while enough to wait and see benzene itself is not very spectacular looking at all it's a colorless compound so that's what it actually looks like but benzene's prayer benzene rings are present in lots and lots of compounds so benzene itself is toxic but lots and lots of compounds with benzene rings in them aren't so benzene as I showed you was in things like aspirin tin as a benzene ring in paracetamol you'll find benzene rings in lots of compounds and so benzene Zin TNT so it's trinitrotoluene which is an explosive so you'll find benzene in a lot of places it's in an amino acid benzene is the simplest example of what is called aromatic compounds I suppose because some of the materials that are made from benzene have a nice smell Nitro benzene which I made at school smells a bit like almonds and a huge number of different chemicals are based on aromatic rings like benzene and one of them for example is terephthalic acid which is what's used in making plastic bottles benzene is also used in lead-free gasoline lead-free petrol because benzene burns differently from straight chains of carbon and hydrogen atoms and so by having benzene in lead-free petrol you can avoid the need to have LED and allow car engines still to function properly because otherwise when you press the accelerator the car starts juddering and doesn't go uphill properly so what we have here now is the benzene in the bottom of the test tube I'm just going to put it in the ice and hopefully we can get it to freeze hope this ice is cool enough wait you see benzene is potentially dangerous but since it is burnt in the car engines the passengers should not really come in contact with it very much but this is why for example you should not try and siphon gasoline out of a car by sucking on the end of a tube to get the siphon going because the benzene in it is poisonous it is not as poisonous as the lead was before but it's still not something that you should be taking into your mouth okay so we're checking up on our benzene we've put we put a little bit of benzene we squeeze a little bit of benzene from this bottle into the bottom of this test tube and we've put it in some system is obviously hopefully the item of water surrounding this is about zero degrees and the melting point of benzene is about five and a half degrees centigrade so it's actually actually should be solid in our ice so if we have a little look at our benzene okay actually it's on its way it's not quite I know actually new is frozen benzene is also used somewhat strangely for making very high purity alcohol if you make alcohol by fermenting glucose in water you get a mixture of alcohol and water and you can then start distilling it however when you distill it you can only get rid of most of the water and you're still left with about two and a half percent of water in the alcohol and however much you distill it you can never get rid of that last bit however if you add a little benzene to the mixture of water and alcohol then the benzene allows you to distill off almost pure alcohol but now you have just a trace of benzene in it and benzene as I said is quite poisonous so this is why you should never try and drink alcohol that's used in the lab because it will contain traces of benzene and could be very bad for you so our bending is is frozen so hopefully if I this upside down fingers crossed it's frozen benzene which freezes at five and a half degrees C

Channel: Periodic Videos

Views: 336,576

Rating: 4.9419107 out of 5

Keywords: benzene

Id: dmqcnlaRA68

Length: 9min 10sec (550 seconds)

Published: Mon Apr 26 2010

Reddit Comments

[u/laughattheleader]

That lab book was bad ass. My old lab books would just get laughed at if I were to show them off.

[u/speckledlemon]

Shucks, I wanted to see the nitration of benzene.

[u/[deleted]]

Wow. This is really cool. My AP Test is in a week and a half and our last unit is organics. We're doing a lot of stuff involving Benzene, obviously. It was really cool to learn that the reason drinking alcohol and lab alcohol are different is because lab alcohol contains Benzene. I would have never guessed. I love Periodic Videos.