Chemical Curiosities: Surprising Science and Dramatic Demonstrations



welcome to this lecture on chemical curiosities I'm going to start with the liquid in this container and I'll just pour some into this cylinder so you can see it's a nice bright red color let's see what happens if I keep pouring I think you can see every time I pour out the liquid I seem to get a different color so in the dictionary the word curious is defined to being something which is puzzling or surprising or unexpected and this demonstration might seem rather puzzling at first until we realize that the cylinders were not empty at the start each of them had a little speck of chemical which reacted with the liquid in this container and it produced a color change and look at the chemistry of that in just a moment let's have a look at the liquid in these two beakers they're both colourless let's see what happens when I pour the liquid from this beaker into this one so again we see a color change it's turning blue the blue is getting darker as I keep pouring goes away again that's also rather odd it seemed as if a chemical reaction began and produced a color change and then it sort of changed its mind and went backwards so did it go backwards did that chemical reaction go backwards so the chemistry of these demonstrations is based on a simple idea which is that every substance can be thought of as either an acid or an alkali and if it's neither if it's sort of in the middle we say that it's neutral now we can use certain substances to tell us whether a material is acid or alkali and probably one of the most famous of these is called litmus so litmus is a material which is red in acid conditions and it's blue in alkaline conditions with lots of other indicators are normally used in this experiment what's called universal indicator so this has a range of different colors it's red when things are strongly acidic in the middle if things are neutral it's green and in strongly alkaline conditions it's purple and this experiment is based on an indicator called final faylene which is colorless in acid and it's blue in alkaline conditioners so these cylinders had different amounts of acid and alkaline than producing the various different colors in this experiment the first beaker had a mixture of final faylene and some acid and the second beaker had some alkali and the key to this is that when acid mixes with alkali they react to produce a salt plus water so they're sort of opposites they kind of cancel each other out so as I started to pour the liquid the acid and final failing from here went into the alkali that the alkali quickly canceled out the acid so the final failing is now an alkaline solution it turns blue but as I keep on pouring I'm adding more and more acid it's neutralizing the alkali and eventually this beaker becomes acid as well and the final failing goes back to being colorless so this reaction was not going backwards it was just the same reaction all along we could ask is there a chemical reaction that goes backwards can Kemah Corrections go backwards at all well it turns out to be a really interesting question and it's a question that we're going to come back to several times during the course of this lecture let me just show you now another example of a reaction involving universal indicator and it's this column of water which has Universal indicator and also a little bit of sodium hydroxide which is alkaline and so it's turned it this sort of bluey purple color I'm going to add some acid and we should see it go through a sequence of colors rather like these now the particular acid that I'm going to use is I see if that's going to be made in the water from carbon dioxide so in this beaker I have carbon dioxide but it's frozen it's at minus 79 degrees centigrade it's become a solid we call this dry ice because when it warms up it doesn't melt to a liquid it goes straight to a gas so it's always dry so I add the dry ice to the water it will react with the water to form an acid called carbonic acid that's the same stuff that's in fizzy drinks that's what gives the fizzy drinks their fizz so let's see what happens when I when I add this now watch for the color changes you should see that sequence of different colors okay so in all the reactions we've seen so far we mix two things together it produced a chemical reaction which gave rise to a color change so let's have a look at this flask this flask has a colorless liquid in but if I shake the flask it turns blue that's a bit surprising because I didn't seem to be mixing two things together I was just shaking up a single liquid here's another flask it's a similar idea this is a yellow liquid if I shake it it turns red they forgive it a really good shake turns green now something else rather surprising about this as well if we keep watching the green is turning back to red and if we look here the blue is turning back to being colorless in fact the red will go back to being yellow so it's going back through that sequence of colors again and what's more I can even repeat it so if I shake it again goes back to being blue that shake this again goes back to being red and so on if I wait it will go back so again it looks as if we have a chemical reaction that's going backwards the first mystery is why do we have a color change at all I didn't seem to be mixing two things together what we have to remember of course is that this flask not only contains water but it contains a gas in fact the gas is just air and air of course is a chemical and when I shake the flask I'm mixing oxygen from the air with the liquid and that's producing the chemical reaction so the next question is did this chemical then go backwards as it fades from blue to colorless is it the chemical action that's going backwards well unfortunately it isn't because what's happening is there's a second chemical reaction taking place this flask contains a dye called methylene blue and when it reacts with oxygen occurs from colorless to blue but also in the flask is some glucose and that glucose slowly turns methylene blue from blue color back to being colorless and this is the same idea but with a different material called indigo calming so again we didn't have the reaction going backwards but we're going to keep on looking for such a reaction as we go through the lecture so interactions we've seen so far then we mix two things together and we got a color change so let's have a look at what happens when I mix these two colorless liquids together so first of all this machine is just called a magnetic stirrer it just spins this little Magnus and keeps the liquid stirring it's just because I'm too lazy to stand here and stir them by hand so we have a colorless liquid being stirred and we add a second colorless liquid and watch closely and see if you can detect a color change so keep watching okay very strange very strange indeed we mix these two chemicals and it seemed as if no reaction took place we just sat there for 10 seconds and then suddenly it reacted and that seems very odd very surprising but what was really going on what's really going on is that there are actually two different chemical reactions taking place inside this beaker the first reaction was quite a slow reaction there's a reaction between two chemicals that produce iodine she imagined this reaction taking place and slowly releasing iodine into the solution now the iodine would appear as a sort of brown color you can't see the iodine because there's a second chemical reaction taking place there's a material in the solution which is reacting very quickly with the iodine and it's absorbing the iodine as soon as it's produced and the secret to this is to arrange that second material is in short supply so the iodine is being produced slowly it's being mopped up by the second material as soon as it's produced but when that second material runs out after about ten seconds or so the next little piece of iodine to be produced remains in solution because the iodine is a bit hard to see from the back of the room we've added some starch the iodine reacts with the starch and produces a very dark blue color that appears to be almost black okay so that's called a clock reaction so now you understand how that one works and have a look at this one this involves three colorless solutions so I pour that one is are there and I pour this into here again watch closely okay so that's a sort of two-stage plot so I'll leave you to think about how that one might be working so in the reactions we've seen so far then we mix chemicals together and we know that a reaction has taken place because we get a change of color there are lots of other ways that a chemical reaction can show up and one way is called a change of state so the state of something just means whether it's a solid or liquid or gas so something turns from a solid to a liquid or from a gas to a solid that it's changed state so we show you an example of a chemical reaction that involves a change of state so I'm going to use these two liquids I have a red liquid and a colorless liquid what I'm going to do is to pour the colorless liquid onto the red liquid very carefully and try to make two layers that's what I want to happen is for the colorless liquid to be floating on top of the red liquid and in separate layers so they don't mix okay so that's worked quite well so I've got now is one liquid floating on top of another and where they meet they undergo a chemical reaction and are actually making a solid the solid material is formed with the two liquids meet what I can do is to fetch out some of this solid material and as I pull it out of the beaker of course it allows the two liquids to meet each other again and so they react again to form more of this solid so if I'm careful so as I wind I'm pulling up this material and it allows the two liquids to meet again it forms more of this material and this substance that's being formed is actually nylon so we're making nylon as I speak and if I'm careful I'd be able to just keep on turning this and making this long thread of nylon at least until we run out of solutions okay so that's an example then of a chemical reaction that involves a change of state so let's have a look at another reaction that involves a change of state and for this I'd like a volunteer please who would like to volunteer you're very keen come on down let's have a big hand for our volunteer you had like to stand there just pop those on what's your name Dylan all right deal if you stand just there we're going to do some chemistry we're going to make it a solid alright I'm going to start off with a flask that contains a solution of silver nitrate and I'm going to add a little bit of ammonia when I add the ammonia you see that it's forming a sort of brown color and they'll keep on adding the ammonia and in a minute that brown color should disappear they know it's disappeared isn't it now what I'm going to do is to add some sodium hydroxide that's now formed a sort of very dark brown almost a black material so I'm now going to add more ammonia and again I'm good add ammonia until the liquid goes back to being colorless this takes a moment or two there we go and then finally I'm going to add some glucose so there's the glucose and I'm going to put the lid on put a clip on I'm gonna give it to you Dylan I want you to hold that and I want you give it a really good shake that's it really hard shake that's good that's it keep shaking that's it so what's happening inside this flask now if there is a chemical reaction taking place and it's forming a solid and the actual material that it's forming is silver we're making pure silver metal keep shaking it takes about three-quarters of an hour as that's okay it does actually take a minister to you but the how do you shake the better it works so keep shaking don't drop it though okay so metal silver metal is being formed sort of atom by atom and you can see it's all going quite black that's because very finely divided silver is actually black in color what we're hoping is going to happen over the next minute or so is that those particles of silver will start to stick to the walls of the of the flask and as they build up we should see silver metal and in the form of a mirror building up on the inside of the flask and you're all seen those sort of decorations that you get at Christmas those spheres that are shiny and they're made using this chemical reaction they're little balls of glass and the inside is coated with silver using this kind of chemistry doing really well okay I should have a quick look almost there keep going a little bit longer so looking a little bit dark excellent alright give it back to me then right I'm going to take the clip off take out the stopper just wash that off and then a pour out the remaining chemicals and then I'm going to rinse this out with distilled water and rinse it out a second time third time there we go and just look at the baton just dry this off and put the clip back on and if you'd like to just just give that little polish if you like to hold it up by the neck that's it and if we bring a camera in and have a look at this and we've got a lovely silver mirror there we go [Applause] and there okay what I'm going to do is give that to you as a souvenir to take home and you about Jessie let's have a hand for volunteer okay so that's an example of a chemical reaction that produces a change of state I want to show you another example of a chemical reaction again this is going to go from being a liquid to being a solid so in this flask I have a solution of sodium acetate and this sodium acetate SAR liquid as you can see but it would very much like to be a solid I would like to turn into a crystal but it needs a sort of an excuse to get going in the excuse is going to be some little crystals of solid sodium acetate in this dish so watch what happens I pour the liquid onto the crystals I think you can see there the liquid as soon as it touches the crystals is turning into a solid and with a bit of luck we can make a sort of chemical sculpture seems to be working okay so that's a sort of sodium acetate sculpture now oddly enough this actually has a practical application and this is the practical application this is something called a hand warmer and it's a plastic pouch and it contains exactly the same liquid as in this flask it's the solution of sodium acetate and it would like to turn into a solid would like to turn into a crystal but it needs an excuse to get going and the excuse is this little metal disc and if I Jeff flip this disc backwards and forwards that should be enough just to start the crystallization off and there it is and we can see the liquid turning into a solid and as it does so it's actually getting warm so there's actually giving off heat there it is it's turned entirely into crystals it's become quite warm in the process I can put that inside my glove and keep my hands warm for half an hour or so and then I can take this and put it into boiling water for a couple of minutes the crystals will turn back into a liquid I can allow it to cool and they'll stay as a liquid it'll stay like that for weeks or months until I'm ready to use it again it can use it thousands of times okay so that's sodium acetate or sort of chemical sculpture I'm going to show you now another way to make a chemical sculpture and Chris has been preparing this this beaker contains a mixture of para nitro acid analyte and sulfuric acid and Chris has been warming it up and when it's hot enough it will undergo a reaction in which this liquid will turn into a solid this makes quite a bit of smoke so we've got this special hood that will suck away the smoke from the reaction here it goes [Applause] okay so that's a chemical action that involves a change of state so we've seen lots of chemical actions now in this lecture we've seen reactions that produce color changes we've seen reactions that produce changes of state and we're asking ourselves the question could a chemical reaction go backwards now seen several reactions that appear to be going backwards but one when we understood them a bit more carefully we realized no they weren't going backwards so it's still like to understand whether a chemical reaction could ever go backwards now to do that we first of all have to ask only does a chemical reaction happen at all why do chemical reactions happen in the first place well to understand that we're going to look at some very simple chemistry and it's the combustion of hydrogen so Chris has filled a balloon with hydrogen gas and we're going to set fire to the balloon and what will happen is the hydrogen will react with the oxygen in the air and that will produce a small quantity of water vapor and it will also release some energy okay so this is the reaction of hydrogen with the oxygen from the air here we go okay so can we just have a show of hands we put your hand up if you enjoyed that demonstration it's quite a few can you put your hand up if you'd like to see a slightly bigger one okay that's everybody all right come on in Chris [Applause] okay now the last balloon made quite a pop this one is going to make a an even louder pop quite a loud bang in fact I'm standing quite close to this I'm very wearing ear defenders but what you might like to do is to cover your ears for this one because it could be fairly loud okay we'll bring down the lights this is the reaction of hydrogen with oxygen so I think you'll have noticed in that reaction that energy was released clearly so he a lot of noise we saw the flame we saw the lights we could I could feel the heat and probably in the front road could as well so energy was released in that reaction so what's happening is that the starting material the hydrogen and oxygen we're in a sort of state of high energy and as a result of the reaction they move to a state of low energy now the total energy in the world is always conserved you can't create or destroy energy so that difference in energy was given out it's given out in the form of that bang that's the heat and the light and the sound and so on so maybe that's why chemical reactions happen maybe chemical reactions happen because the chemicals moved from the state of high energy to state of low energy and they give out that difference of energy so it's a bit like taking a ball and putting it on a slope if you put a ball on a slope it rolls downhill it goes from the state of high energy to state of low energy so maybe that's how chemical reactions work if it is how a chemical reactions work then it's pretty obvious that a chemical reaction could never go backwards because going backwards would be like putting a ball on a hill and having it decide to roll uphill that's not going to happen okay so we'll keep that thought in mind and we'll look at some other examples of chemical reactions that give out energy now we've seen energy being given out of the form of a bang we saw a little bit of light being given off there in the form of that flame and I want to show you a reaction that gives off a great deal of light and it's a the reaction of a rather special element it's called phosphorus and the word phosphorus comes from the Greek it means the the giver or the bearer of light so this is a reaction that will give out a great deal of light so we could just burn a little bit of phosphorus on the on the bench but we thought we'd do is to scale this up and do this on the largest scale we could and so this is actually the largest flask that you can buy in the UK and so this is about as big as as we can make it and we're going to burn quite a big chunk of white phosphorus inside this flask and Oh make it burn really well we're going fill the flask with pure oxygen now it also fill the flask with pure oxygen we're going to use liquid oxygen and we're going to make the liquid oxygen by starting from another liquefied gas liquid hydrogen so in this vacuum flask I have some liquid hydrogen it's a colorless liquid it looks pretty much like water but it's at a very low temperature is at minus 196 degrees centigrade so just for a little bit of fun I thought we'd see what happens if we take some liquid nitrogen at minus 196 degrees centigrade and pour it into some pretty much boiling water okay and and this is what happens there's no real point to that it was just for fun you understand okay so this liquid nitrogen is extremely cold and we can use it to cool down oxygen gas so that it too becomes a liquid that's what Chris has been doing over here so the cylinder contains oxygen gas and Chris has been passing the oxygen gas through a coil of copper that sat inside some liquid nitrogen and the oxygen has been turning into a liquid itself and so this vacuum flask contains liquid oxygen and I want to show you one interesting thing about about liquid oxygen I'm going to pour it into this test tube and you may be able to see that although the the air the air contains one-fifth oxygen in the air of course is completely transparent and yet oxygen when it becomes a liquid turns this lovely blue color okay so I'm going to use this liquid oxygen then to fill this flask with oxygen so I'm going to pull this in and we'll add a bit more for good measure enough okay and so the oxygen the liquid oxygen is warming up as it touches the flask and it's evaporating and it's turning into oxygen gas and as it as it turns into a gas it's pushing the air you can see the the fumes coming out the top here is pushing the air out of the out of the flask and filling the flask with oxygen and just to help that along a bit I'm just gonna swirl this around okay you can see a little bit of liquid oxygen there that lovely blue color sloshing around at the bottom of this flask so that's gradually evaporating and that's filling the flask with pure oxygen of course we could have just taken a hose from this cylinder into the flask and filled it with oxygen that way but I think this was more fun okay well that last little bit is evaporating the next thing we're gonna do is to get some phosphorous there are two kinds of phosphorous red phosphorous and white phosphorous this is white phosphorous it's the more reactive kind it's so reactive that it actually reacts with the air if you just leave it sitting on a bench should catch fire after a few minutes and so we store it underwater I'm gonna fetch out this piece of white phosphorus and we're going to put it in a little spoon that's suspended from the lid of the flask okay you can see the phosphorus is smoking already as it comes into contact with the air and that will probably catch fire sometime in the next few minutes but just to help it along I'm going to take a glass rod and heat up the end of the rod and then just touch that against the phosphorus just to get things going and as as soon as the phosphorus ignites we'll bring down the lights what you'll see is the reaction of phosphorus burning in pure oxygen you can see this lovely white light being given out it's a very vigorous reaction the flask is filling with oxides of phosphorus so that's white phosphorus the bearer of light [Applause] okay so that's a chemical reaction then which gives out energy in the form of light I'm going to show you another reaction now which gives out energy again in the form of light but also in the form of sound this is a reaction between a colorless gas which is in this glass tube called nitric oxide and a liquid called carbon disulfide so this is the carbon disulphide and we're going to add some of this to the tube and then we're gonna mix them together so Chris is going to mix the carbon disulfide with the nitric oxide the carbon disulfide evaporates and turns into a gas we've got a little bit of water in the tube just to help them mix and when they're thoroughly mixed we'll set fire to it now this happens this reaction happens reasonably quickly so just bring the light stand first so you've seen a couple of reactions there that involve effectively combustion and combustion can give rise to some very interesting chemistry and for this I'm going to set fire to a brand-new 50-pound note there's an example of combustion so let me soak the 50-pound note in some flammable liquid and then we'll set it on fire so this is this is my 50 pound note it's brand-new and there it is on fire and the flames have gone out but the 50 pound note I'm pleased to say is entirely intact I'm very pleased about that now the reason that the 50 pound note survived has to do with the choice of liquid so this liquid was 50 percent alcohol which is inflammable and 50 percent water and it was the water that protected the 50 pound note it absorbs heat and it stops the note from burning so really that's not too surprising because we know that we use water to put out fires the fire brigade carry water with them they have hoses they use water for fire extinguishing so let's have a look at some different ways of putting out fires and I've got here three fire extinguishers based on different kinds of chemistry now it'd be very surprising wouldn't it if we could use a fire extinguisher not to put out a fire but to make a fire worse it'd be really surprising if we could use a fire extinguisher to start a fire okay let's look at the first kind of fire extinguisher so this is called a water fire extinguisher it contains water under pressure when you let the extinguisher off the water comes out of the hose you soak the fire and you put the fire out now if I let that off in here it were just a flood the lecture theatre so we'll do something else that that's equivalent from the point of view of chemistry and and that's to use a water pistol so this water pistol contains just ordinary tap water I can pressurize it and you can be careful what you wish for so this is just like that water fire extinguisher it's squirt suggestive water so could we use this to start a fire well for this I'd like a volunteer please who would like to volunteer you're very quick of a hand for volunteer please and what's your name Chiara right Chiara if you want to put on these safety goggles they're special safety goggles because they're tinted a nice trendy shades all right and what you're going to do is to squirt the water pistol at a little metal dish can you see that on the little stand there and that dish contains the mixture of silver nitrate and finally powdered magnesium and if you can get a little bit of water to land on it we'll see if that can start a fire now because this contains magnesium it's going to produce a very bright light so my suggestion and my recommendation is that you don't look directly at the dish but instead you look to one side now you do need to look at the dish because you need to see if you can hit it with water so that's why we've given you these special goggles alright so off you go see if you can get a bit of water into that dish oh well done thank you very much [Applause] okay so that was the first kind of fire extinguisher that's that's the water-based fire extinguisher so if you see a little fire involving magnesium and silver nitrate don't try to put it out with that this is the next kind of fire extinguisher it's got a carbon dioxide fire extinguisher and it contains liquid carbon dioxide under very high pressure so just pull out the pin and with the nozzle up we'll just set this off okay so as you can see the liquid carbon dioxide under very high pressure comes out through the nozzle and it turns into a gas now carbon dioxide is often one of the main results of combustion if something like wood or paper is burning the carbon reacts with the oxygen in the air to produce carbon dioxide so the carbon dioxide is the end product of combustion that's why it's good for putting out fires so we use the carbon dioxide fire extinguisher to smother a fire to exclude the air and therefore exclude the oxygen and then the fire goes out so it'd be a bit odd if using a fire extinguisher like this would actually make the fire worse rather than better well let's see what that might look like so again we're going to use carbon dioxide in a very concentrated form in the form of solid carbon dioxide or dry ice which is something that we saw a little bit earlier in the lecture so this is a block of dry ice and again we're going to use magnesium so I have some magnesium metal here and we're just going to make a little pile in a little trough that we've cut inside the block and I'm going to set fire to the magnesium and once it's on fire Chris is going to put the the other half of the block on top and then the magnesium will be sort of trapped inside and if we bring the light stand and you can see the combustion is becoming more vigorous this is magnesium burning in carbon dioxide so it's not putting the fire out it's actually supporting combustion giving off this beautiful light the white smoke you see is magnesium oxide this is the sort of stuff that's used in indigestion tablets that kind of thing I wouldn't recommend that for dealing with indigestion so the magnesium combines with the carbon dioxide to make magnesium oxide and carbon thank you okay we have a third kind of fire extinguisher and that's this one this is called a dry powder fire extinguisher it contains a powder and it's pressurized when we set this off the powder comes out of the hose and we can squirt it at the fire and put the fire out now these are actually extremely good fire extinguishers if you have an extinguisher in your kitchen or one in your car it's probably a dry powder extinguisher and these extinguishers usually contain something like sodium or potassium carbonate or sodium or potassium bicarbonate they're very effective extinguishers they're good for dealing with all kinds of fire and it would be very surprising if using the powder out of one of those could actually make combustion faster or make it worse well perhaps it can in this spoon we have a gram of commercial gunpowder it's made from a mixture of three ingredients saltpeter whose chemical industry TAS iam nitrate and that acts as a source of concentrated oxygen you call that an oxidizer it contains charcoal which acts as the fuel and that burns in the oxygen released by the potassium nitrate and it contains sulfur and the sulfur is there to aid combustion to make the gunpowder burn more easily what would happen if we took gunpowder and instead of using charcoal which is the main fuel we use some of the powder from a fire english' so this seems pretty odd we're going to take away the main fuel from the Gunpowder and we're going to replace it with something that's used in a fire extinguisher that we're going to use potassium carbonate for this so if you mix those three things together that is potassium nitrate potassium carbonate and sulfur we get something called yellow powder and so in this spoon we have a gram of black powder and in this spoon we have a gram of yellow powder now we're going to do is to heat up these two spoons and we'll see if there's a difference between these two powders so there's the gun powder and this is the yellow powder now gun powder when it burns in the open doesn't make a bang it just burns with a puff and a little cloud of smoke so we're not expecting the gun powder to make a bang the yellow powder however very probably will make a bang and it could be fairly loud so sometime in the next minute or so there could be quite a loud bang and you might wish to cover your ears for this now as the spoons heat up at some point the gun powder will get hot enough that it will ignite and we'll see a puff of smoke the yellow powder is a little bit different inside that spoon the materials are starting to melt they're flowing together and some chemistry is taking place the chemical composition is actually changing there as a result of being warmed up and at some point that new mixture of chemicals should give rise to a little explosion because if the gun and a beautiful smoke ring [Applause] [Applause] okay so that's that's some of the science of combustion and that's how the powder from a powder a dry powder fire extinguisher could actually make combustion a little bit worse so if you remember one of the questions that we're asking in this lecture is whether a chemical reaction can go backwards and I said this is a very interesting question well let me show you a fascinating reaction so in this beaker is a colorless liquid I'm going to add a second color las' liquid it remains colorless I'm going to add some yellow liquid and it turns orange right a little bit of red liquid and it goes sort of green color kind of muddy color now in a minute or so that muddiness will fade away or we'll be able to see the color of the solution and what I want you to do is to watch the color of this solution as it changes and there's a rather interesting story behind this reaction it was first discovered in about 1951 by a Russian chemist called Boris bellows off and he was trying to study the way citric acid behaves in the human body and so he was mixing various materials together in a in a beaker and he discovered some very interesting color changes and in particular he discovered an oscillating chemical reaction that is a chemical reaction that went through a sequence of color changes and then came back to the starting point so you can see that muddy color is fading and we've now got you've got a green solution and the solution is now gradually turning blue so remember that it started out green and it's turned blue now Bella softride – he was very excited by the idea of an oscillating chemical reaction that's sort of like a reaction that goes backwards and people thought that reactions didn't do that sort of thing so he wrote this up and he sent it off to the top chemistry journal in Russia and the editors looked at this and they rejected the paper because they said that couldn't happen okay it's now turned from blue to red red green blue red so when Assaf had his paper rejected as we sent it to another journal and they did the same thing they rejected as well because they thought Timah Corrections just shouldn't behave like this there must be something wrong so he got pretty depressed about this in fact he got so depressed he actually gave up being a scientist and his discovery was sort of forgotten and then about 10 years later a student of chemistry Anatole zhabotinsky a Russian student discovered very soft notes that's turned back to blue that's turned green alright so remember that sequence were green for little while then blue that it went red then back to blue briefly now it's green so zhabotinsky discovered bela salsa notes and he recreated this experiment and he was able to get this published the conference in Vienna and then the whole world knew about it it became quite a sensation and people got very excited about these kinds of reactions so you see it's gone back to blue it's now turning back to red and it will keep going through that sequence of colors so it seems as if we have a reaction that sort of goes backwards or at least it goes round in a cycle so lots of people started to study these reactions and they came up with other kinds of oscillating reactions but I want to show you one that has quite a nice story to it because this was discovered not by professional chemists but by a couple of school teachers and their names were Briggs and rasher and they were working in a high school in San Francisco and they were using the school chemistry labs our four hours and they discovered a different kind of oscillating reaction so again I have a clear liquid I had a second clear liquid and a third clear liquid and it turns amber and we keep watching it turns blue very dark blue so there's a little bit like the clock reaction it's the same thing at the reaction between starch and iodine but this time it doesn't stay blue it's going clear again so it's become clear now it's going back to amber and if you keep watching back to blue again okay so those are two oscillating chemical reactions so it seems as if we found a chemical reaction that does actually go backwards but really that isn't what's happening it's not like a ball rolling downhill and then changing its mind and rolling back uphill again it's more like a ball going down a sort of a helix it gets back to the same color as when it started but it's not really in the same condition because some of the chemicals have been used up and we can watch these oscillations happening but after ten or twenty minutes they will come to a stop and that's because the chemicals have been used up so we haven't really found a reaction yet that can go backwards so does that mean that our theory of chemical reactions is correct remember our theory is that chemical reactions are like a ball rolling downhill the chemicals go from high energy to low energy and they give out that energy difference in the form of heat or light or sand or whatever well let's look at this reaction this is a reaction between two powders so in this beaker is some barium hydroxide it's a white powder I've got a block of wood I'm just going to put some water on the surface of the wood to make a sort of puddle and I'm gonna stand the beaker in the puddle and then in this beaker in this flask I have some ammonium chloride so I'm going to add the ammonium chloride to the the barium hydroxide and I'm going to stir it using this pro which is attached to this thermometer this digital thermometer you can see the temperature there is about 20 degrees well let me start to mix the powders together and we'll see what happens to the temperature so the temperatures falling very quickly well below 10 degrees now and the temperatures just gone negative this is now below naught degrees so it's a minus 7 degrees so the temperature is falling very rapidly the other thing that's happened is that it's turned from a solid into a liquid so it's now become a sort of slushy white liquid the temperature is down at minus 15 degrees so well below the freezing point of water now remember I stood it in a little puddle of water so what should have happened is that water should have frozen and there we are it's frozen it to the block of wood [Applause] so that's pretty strange because that's a reaction that didn't give out energy it's a reaction that took in energy it actually took in heat from the surroundings and that's why the surroundings such as the thermometer dropped in temperature so that's a bit like putting a ball on a slope and seeing the ball roll uphill right it shouldn't happen so this is a very strange reaction and it means that our theory of why chemical reactions happen isn't quite right or at least it isn't complete there's something else that's missing so what's missing in our theory of how chemistry happens what I'm going to illustrate this with a little computer game what we got here are hundred disks and each disk is yellow on one side and it's red on the other and the bar down the right-hand side shows you the proportion of disks which are yellow and I've started them all off as yellow and let's see what happens when we run the little simulation so about a hundred times a second the computer is choosing a disk and it's deciding either to keep it the same color or to flip it over and you can see on the right-hand side the proportion of red and yellow now we started off with all the disks yellow and very quickly we've got to a state where about half of them are red and about half of them are yellow let's try it again this time we can set them all to red again we'll run the little simulation they start off all red but very quickly they come to a state where about half of them are red and about half of them are yellow so I'm going to say this is the thing that we started the disks off in a very ordered State they were all the same color and as the simulation rang the level of disorder increased okay it went from a an ordered state to a more random state and this is such an important idea we give it a special name we call the degree of disorder entropy and we say that entropy tends to increase with time we started off with things very ordered and they became very disordered and the reason this happens is very simple it's because there's only one way for the disk to be all yellow but there are lots and lots and lots of ways for the disks to be sort of roughly half yellow and half red and so it's just simply counting the number of different ways of arranging these disks that causes the disks to go from an ordered state to the disordered state now you might think well well hang on a moment if we wait long enough sooner or later by chance all of the disks will become yellow again so the system would then have gone from the disordered state to an ordered state now you're absolutely right you'd have to wait a long time this is doing about a hundred flips a second if we did a trillion flips a second you would still have to wait longer than the age of the universe on average before you see them all yellow again so it's almost certain that the world will move from an ordered States to a disordered state I've got a couple of teenage boys and their bedrooms provide a perfect illustration of this if I tidy their bedroom so everything is very ordered and come back the next day it's almost certain to be in a highly disordered state and without input from me it will never go in from being disordered to being ordered so that's the idea of entropy entropy increases and that can drive a chemical reaction so let's think about a solid in a solid the atoms or the molecules arranged in nice neat rows they're very ordered in a sort of crystal lattice in a liquid the molecules can move around they're not in fixed positions anymore so this is a more disordered state than a solid and a gas is even more disordered because the atoms or the molecules are free to move around they can fill the container so as we go from solid to liquid to gas the entropy or the disorder increases there are two things that can drive chemical reactions is the ball rolling downhill effect the decrease in energy or there is the increase in entropy the sort of teenager bedroom effect this reaction is being driven by that increase in entropy it's gone from a sword to a liquid and that increase in entropy is so big that it overcomes the fact that it actually has to increase the energy for that reaction to happen and so that reaction happens spontaneously and it's draws energy in from the environment and cools its environment down so that's why that reaction happens so that means that we have two things that can drive chemical reactions it's not just the ball rolling downhill it's also the the the bedroom effects and so perhaps now that we have that deeper understanding of chemistry perhaps we can now find a chemical reaction that goes backwards well to help us find this I'm going to use the word curious in a different sense we've used curious to mean strange or surprising or or unexpected that curious can also refer to a desire to learn – curiosity I'm going to tell you a story about curiosity in a young chemist so his name was IRA remson and as an adult he became very famous he founded the chemistry department at John Hopkins University and he discovered the first artificial sweetener that's called saccharin but as a teenager he was curious about chemistry and he used to do some little experiments and I'm going to tell you a story in his words about an experiment which he performed when he was a youngster now the experiment involves the reaction between copper and nitric acid and so when we get to the appropriate point in the story I'm actually going to show you the reaction and the reactions going to happen in this flask in this cylinder at the top we have some nitric acid and in the flask we have copper now the copper as you know for reasons you'll see in a moment is in the form of a coin and we can't use a modern a penny or two penny piece because they're actually made of steel with just a thin coating of copper so I've got an old-fashioned penny here this was made in 1945 so this is actually made of solid copper so we put one of these pennies into the flask and we're going to do this reaction in a sealed environment in a sealed flask any fumes that are produced will be led away through this tube and absorbed in this sodium hydroxide for reasons that will become apparent in a moment okay so this is the story of IRA Remsen while reading a textbook of chemistry I came across the statement nitric acid acts upon copper I was getting tired of reading such absurd stuff and I determined to see what this meant copper was more or less familiar to me for copper cents with any news I'd seen a bottle marked nitric acid on a table in the doctor's office where I was then doing time I did not know its peculiarities but I was getting on and likely to learn the spirit of adventure was upon me having nitric acid and copper I had only to learn what the words act upon meant then the statement nitric acid acts upon copper would be something more than mere words all was still in the interest of knowledge I was even willing to sacrifice one of the few copper cents then in my possession I put one of them on the table opened the bottle marked nitric acid poured some of the liquid on the copper and prepared to make an observation so let's add the nitric acid to the copper and see what happens I think you can see that quite a vigorous reaction is taking place sort of green liquid it's bubbling away some fumes are coming off all right let's continue with the story but what was this wonderful thing which I beheld the scent was already changed it was no small change either a greenish blue liquid foamed and fumed over the scent and over the table the air in the neighborhood of the performance became colored dark red a great cloud arose this was disagreeable and suffocating how should I stop this I tried to get rid of the objectionable mess by picking it up and throwing it out of the window which I had meanwhile opened I learned another fact nitric acid not only acts upon copper but it acts upon fingers the pain led to another unpremeditated experiment I drew my fingers across my trousers and another fact was discovered nitric acid acts upon trousers taking everything into consideration that was probably the most impressive experiment and relatively probably the most costly experiment I have ever performed I tell you that even now with interest it was a revelation to me it resulted in a desire on my part to learn more about that remarkable kind of action plainly the only way to learn about it was to see its results to experiment to work in a laboratory so that's the reaction of nitric acid with copper and it's produced these dark brown fumes which you can see and those fumes are called nitrogen dioxide and they are actually pretty unpleasant which is why we're doing this in a SCL apparatus but now shouldn't dioxide is a material that can help us understand this question about whether a chemical reaction can go backwards so in these tubes we have equal amounts of nitrogen dioxide and what I'm going to do is to take one of the tubes and to place it in iced water so that it will cool down and the other tube I'm going to place in hot water to heat it up so we'll come back in a moment and see if they're changed in any way so let's have a little look at the chemistry that's going on inside those tubes now nitrogen dioxide has a molecule which consists of one atom of nitrogen and two atoms of oxygen if we have two molecules of nitrogen dioxide they can react together to form one molecule of another oxide of nitrogen called dummy nitrogen tetroxide now that process releases energy when that extra nitrogen nitrogen bond is formed it gives out energy so that's like the ball rolling downhill the ball rolling downhill wants the notion dioxide to come together and form dinitrogen tetroxide with the dinitrogen tetroxide can split up the molecule can split in half to give two molecules of nitrogen dioxide and because for every molecule of dinitrogen tetroxide we get two molecules of nitrogen dioxide we have twice as many molecules they can be arranged in many more ways and that means the entropy has increased so the entropy tends to drive this reaction from the right to the left so these two effects the ball rolling downhill effect and the teenager bedroom effect are driving this reaction in sort of opposite directions what happens is that the reaction actually goes in both directions at the same time and it reaches a sort of balance we call it an equilibrium where there is some nitrogen dioxide present and some dinitrogen tetroxide present and the relative proportions of these depends upon the temperature so if we increase the temperature we put energy into the system that's like pushing the ball uphill we go from right to left and if we cool the system bang then conversely we go from left to right so that's the prediction and we can test the prediction because nitrogen dioxide is this dark brown gas that you see in the flask here but dinitrogen tetroxide is colorless so if we go back to our tubes this is the tube that was in the cold water and you can see that it's become a paler color and this is the tube that was in the hot water so I just put these side-by-side you can see that heating up this gas has made it darker Brown contains more nitrogen dioxide whereas cooling it down has made it less dark and contains more dinitrogen tetroxide and just to check our theory what we can do is we can take the hot tube the dark tube and place it into the cold water and then the the cold tube which is the paler color we can place that into hot water and we'll come back and have a look at those in a moment and we'll see if they've swapped places okay so that really brings us towards the end of the lecture what I want to do is just to show you one more curiosity and it concerns a rather interesting and unusual element now this element was discovered in a mine in outside a little town called Iturbi which is near stockholm in sweden and they had been extracting minerals from the mine and they found a mineral that seemed rather peculiar they couldn't understand what it contained until they realised that it contained a new element this was sort of the beginning of the 18th century now in those days if you discovered a new element you got to choose its name and they decided to name the element after the town of Iturbi and this element is called yttrium what rather interesting is that this mineral contained not just one new element where they found out it contained four new elements and so they decided to name all four elements after the town of its Herbie so these four elements are called yttrium ytterbium erbium and terbium which is a little bit confusing I think we can look at the first of these yttrium now it reom can be used to make a compound and I have some of the compound here it's called yttrium barium copper oxide and it's just a hard black lump of ceramic material what I'm here to do is to put it into some liquid nitrogen and so that it tree and barium copper oxide is now being cooled down to minus 196 degrees it takes a moment or two to cool down so while we're waiting I also have in this cup another piece of identical material exactly the same as the first and I'm going to cover this in liquid nitrogen so that too can be cooling down now at room temperature this material isn't very remarkable but when it gets sufficiently cold it has a very interesting a very strange property becomes what we call a superconductor now a superconductor is a material that has lost all its electrical resistance a material which has zero electrical resistance has the property that it can repel a magnetic field so this ring is a ring made of steel and it's covered in little magnets very strong magnets they alternate North Pole South Pole north pole and so on and in a minute when this is cooled down we're going to see if that it reembarked side can repel the magnetic field produced by these magnets this just takes a a moment or two to cool down so if I look in here I can see they're boiling away very vigorously that means the the ceramic material is giving up its heat to the liquid nitrogen is boiling the liquid nitrogen away and and cooling down in the process so essentially I'm just waiting for the boiling to stop when it stops boiling that means the ceramic material has reached the same temperature of the liquid nitrogen so will then be at minus 196 degrees okay so let's fetch this out then and let's see if this can repel magnetic field [Applause] okay so this is actually quite a special kind of superconductor it's what we call a type 2 superconductor and that means that as well as a repelling magnetic field it can also trap magnetic field now remember I've got another one of these sitting inside this polystyrene Cup and underneath is a cylinder and on the top of the cylinder is a very strong magnet now the field from that magnet was already passing through the ceramic material before I added the liquid nitrogen so I've now cooled it down it should have become a superconductor and hopefully it will have trapped that magnetic field so it should still be gripping onto that field that means I should be able to take away the support from this cylinder and by the way on the outside of the cylinder we've put the logo for the International Year of chemistry 2011 has been a year-long celebration around the world of the delights of chemistry and as the importance of chemistry for our everyday lives and I thought it would be a nice way to just mark that occasion so I think this has cooled down now so I'm going to see if I can lower this very carefully [Applause] [Applause] okay well thank you very much that that pretty much brings us to the end of the lecture just before we wrap up I thought we would we've finished with with a rather nice demo but just before we do I just want to ask you to join me in thanking somebody who's put a lot of effort into helping me prepare and deliver this lecture and that's Chris Braxton [Applause] okay just before we finish I thought we'd take a look at this block of dry ice if you remember we burned some magnesium inside this block of dry ice so the chemistry here is that the magnesium reacted with carbon dioxide to produce magnesium oxide and carbon and if we look at the surface of this we can see that it's coated in a white powder and that's the magnesium oxide and if we dig down inside the black powder is the carbon and then finally we swapped those two tubes over we put the dark tube inside the iced water and we put the white color tube in the hot water and we can see they have indeed swapped places so the tube that was dark has been cooled down has become light and the light color tube has been heated up and it's become dark so we have the rather curious conclusion that chemical reactions can go forwards and backwards at the same time all right well that really is the end of the lecture but I thought we'd have just one more demonstration to finish and I thought what we would do is to repeat one of the earlier demonstrations it's the demonstration of the reaction between nitric oxide and carbon disulfide but I thought we'd do it on a slightly bigger scale so Chris is bring you on a tube of nitric oxide so I'm going to add the carbon disulphide again Chris is going to mix these together and once they're thoroughly mixed we'll set fire to the end of the tube all right and we'll put the lights down for this just like to say thank you all for coming here we go [Applause] [Applause] you

49 thoughts on “Chemical Curiosities: Surprising Science and Dramatic Demonstrations

  1. If kids spent as much time learning this as fortnite and minecraft we would have a cure for cancer in 1 year.

  2. *=* Strange echoes sound between 0:15 and 1:45, lol ?
    34:26 Wow, rocket nozzle ?
    35:37 Interesting inverted reaction, CO2 to C by Mg making MgO, and the final reaction 1:06:50, about chlorophyll chemistry ?

  3. This guy is polymath. His PhD is in THEORETICAL PHYSICS, and is currently a Professor of COMPUTER SCIENCE at the University of Edinburgh. In 2004, he was elected Fellow of the Royal Academy of ENGINEERING and is also a Microsoft Technical Fellow and Director of the Microsoft Research Lab in Cambridge, UK.

    CHEMISTRY doesn't seem to be included in any of his bios, maybe he mastered it in his free time.

  4. If this were Mr. Bean, I would be impressed, but sadly, there is a severe lack of Mr. Bean. I’m going to have to rate this a 4/10

  5. this lecture is basically a copy of the one from Andrew Syzdlo. he has a few different ones and so far this is like watching a re-run with a younger more boring teacher. even the same jokes…Andrew is definitely funnier !!!

  6. Burn H2 (2*H2 + O2 -> 2*H20). Then electrolyze the water (2*H20 -> 2H2 + O2)… Is a reaction that goes backwards..

  7. Hi, This is an amazing video. This resource will be very helpful for children. But the video is in English. Majority of the children in India study in vernacular languages. We, Pratham Education Foundation an NGO working in the field of education is trying to find a solution to this difficulty. We are trying to develop as well as outsource resources and translate it into all Indian languages. I have sent an email to [email protected] regarding the same. I request your attention to this.

  8. Isn't the hand warmer 17:30 a chemical reaction going in both ways, if you just can boil it and it goes back, and then flick the metal and make it crystal again?

  9. Wonderful lecture, however two points are misrepresented, when the solution went from liquid to crystal that was not a chemical reaction but a phase change of a supersaturated solution (technically thermodynamics). Second the superconducting magnet also did not undergo any chemical change instead it was a physical one as it was cooled. Otherwise outstanding.

  10. silver is elemental. unless the silver was in compound going in, it will not b created, only reveiled. not worthy of clapping because there was bad data (not a lie).

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