Chemical Curiosities: Surprising Science and Dramatic Demonstrations


welcome to this lecture
on chemical curiosities I’m gonna start with the liquid in this container
and I just pour some into this cylinder since 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 mean 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 we’ll look at
the chemistry of that in just a moment let’s have a look at the liquid in
these two beakers they are both colorless 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 thats also rather odd
it seems as if a chemical reaction began
and produced the 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 is 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 its blue in alkali
conditions and there are lots of other indicators. I normally used in this
experiment was called universal indicator this has a range of different
colors it’s red when things are strongly acidic in the middle where things are neutral its green
and in strongly alkaline conditions its purple and this experiment is based on an
indicator called thymolphthalein. which is colorless
in acid and its blue in alkaline conditions so these cylinders had different amounts of acid
and alkaline in them producing the various different colors in this experiment the first beaker
had a mixture of thymolphthalein 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 are sort of opposites
they kind of cancel each other out so as I started to
pour the liquid the acid and final fehling from
here went into the alkali the alkali quickly cancelled out the
acid so the final fehling is now an alkaline solution that turns blue but as I keep on pouring I’m
adding more and more acid its neutralizing the alkali and
eventually this beaker becomes acid as well and the final fehling 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 chemical reactions go backwards at
all well it turns out to be a really interesting question
and it’s a question that we gonna come back to several times
during the course of this lecture but let me just show you
now an other 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 gonna add some acid we should see it go through a
sequence of colors rather like these now the particular acid that i’m gonna use
is acid that’s going to be made in the water from
carbon dioxide so, in this beaker I have carbon
dioxide but it’s frozen its at -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 the gas its always dry so when I add the dry
ice to the water it will react with the water to
form an acid called carbonic acid thats the same stuff that’s in fizzy drinks thats
what gives the the fizzy drinks that fizz so let’s see what happens
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 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 i was just shaking up a single liquid here is another flask it’s a similar
idea this is a yellow liquid if I shake it it turns red if we gave it a really
good shake it turns green there is 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 infact the red will go back to being
yellow so it’s going back through that sequence of colors again what’s more I can even repeat it so If I
shake it again goes back to being blue 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 but
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 reaction then go backwards as it fades from blue to colorless is it
a chemical reaction that”s going backwards well unfortunately it is’nt because
what’s happening is there’s a second chemical reaction taking place this flask contains a dye
called methylene blue when it reacts with oxygen it
goes from colorless to blue but also in the flask there is some glucose
and that glucose slowly turns methylene blue from blue-color back to being
colorless this is the same idea but with the different material
called indigo carmine so again we didn’t have a
chemical reaction going backwards but we’re gonna keep on looking for such
a reaction as we go through the lecture so in the reactions we’ve seen so
far then we mix to things together and we got a color change so let’s
have a look at what happens when i mix these two colorless liquid together so
first all this machine is just called a magnetic stirrer it just spins these little magnets and keeps
the liquid stirring it’s just because i’m too lazy to stand here
stir them by hand so if a colorless liquid being stirred
i’m gonna add a second colorless liquid and watch closely and see if you
can detect a color change so keep watching (Audience surprised) okay (Laughing) very strange, very strange indeed, we mixed
these two chemicals and it seemed as if no reaction took place we just sat there for 10 seconds
and then suddenly it reacted now 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 it was a reaction between two
chemicals that produced Iodine so imagine 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 is being mugged up by the second
material as soon as it’s produced when that second material runs out
after about 10 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 thats
called a clock reaction so now you understand how that one
works. Have a look at this one this involves three color
solutions so I poured out one into there and I pour this
into here again watch closely okay so thats a sort of two-stage clock
so i 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 had a change of color but 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 to a solid to liquid or from a gas to the solid then it’s changed state
so we show you an example of a chemical reaction that involves a change of state so we will 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 so what I want to happen is for the
colorless liquid to be floating on top of the red liquid in in separate layers that they don’t
mix so that’s worked quite well so what i’ve got now is one liquid
floating on top of another and where they meets they undergo
a chemical reaction and they’re actually making a solid
a solid material is formed where the two liquids
meets 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 and it forms more this material and this substance that’s being formed is
actually nylon so we’re making nylon as I speak and if I’mcareful I’d be able to just keep on turning this
and making this long thread of nylon atleast until we run out of solutions. Okay so that’s an example of a chemical reaction that involves a change of state. So let’s
have a look at another reaction that involve a change of state and
for this i’d like a volunteer please … who would like to volunteer you are very keen, common, lets have
a big hand for our volunteer, you would like to stand
there, put those on what’s your name ? Dylan. Dylan, alright
you stand just there we gonna do some chemistry we gonna
make a solid alright I’m gonna start of with a flask that contains a solution
of silver nitrates and I’m going to
add a little bit of ammonia now when i add the ammonia you see that it’s forming
a sort of brown color now keep on adding the
ammonia and then in a minute brown color should disappear
that’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 black material so now I’m going to add more ammonia and again I’m going to add ammonia untill
the liquid goes back to being colorless It takes a moment or two there we go and then finally
I’m going to add some glucose so there’s the glucose
I’m gonna put the lid on with a clip-on I’m gonna give it to you Dylan and I want you to hold that and I want you to 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 is
there’s 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 is
that okay (Audience laughing) … it does actually take a minute but the harder you shake the better it
works so keep shaking don’t drop it. okay so metal silver metal is
being formed an 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 gonna happen
over the next minute or so is that those particles of silver will start to stick to the walls of the flask
and as they build up we should see a silver metal in the form of a mirror building up on the
inside of the flask and you’ve all seen those sort of decorations
you get it in Christmas those spheres that are shiny and they are made using this chemical
reaction little balls of glass and the inside is coated with
silver using this kind of chemistry doing really well okay
so I have quick look almost there keep going a little bit
longer so it looks a little bit dark excellent alright give it back to me
then right let me take the clip off you take out the stopper just wash that off and I pour out the
remaining chemicals and then I’m going to
rinse this out with distilled water and I’m going to add a second time third time there we go and just look at that one let’s dry this off and
then clip back on and if you like to just
give that a little polish if you’d 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 ok what I’m gonna do is give that to you. Take that to home and you can go back to your seat,
lets have a hand for our volunteer ok so that’s an example
of a chemical reaction the produces a change of state and 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 is a liquid as you can see, but it would very much like to be a solid it would like to turn
into a crystal but it needs a sort of an excuse
to get going and the excuse is gonna be some little crystals
of solid sodium acetate in this dish so watch what
happens if I pour the liquid onto the crystals I think
you can see that 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 what we’ve learned is that this actually has a
practical application in this is the practical application this is something called a hand warmer and it’s a plastic patch and it contains
exactly the same liquid as in this flask this is a solution of sodium acetate and it would like to turn into a
solid it would like to turn into a crystal but it needs some excuse to
get going and the excuse is this little metal
disc and if I just flip this disc backwards and forwards
that should be enough just to start the crystallization and
there it is and we can see the liquid turning into a
solid as it does so its actually getting warm
so it’s actually giving off heat and there it is it has turned entirely into crystals it’s become quite
warm in the process and 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 that’ll stay as
a liquid that will stay like that for weeks or months until I’m ready to use it again
we can use it thousands of times okay so that’s sodium acetate
it’s a sort of chemical sculpture I’m gonna show you now another way
to make a chemical sculpture and chris has been preparing
this this beaker contains a mixture of para nitro acetanilide 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 goesokay so that’s a chemical reactions
that involves a change of state so we’ve seen lots of chemical reactions now
in this lecture we’ve seen reactions that produced color changes we’ve
seen reactions that produce changes of States and we’re asking
ourselves the question could a chemical reaction go backwards
you may have seen several reactions that appear to be going backwards but when we understood them a
bit more carefully we realize no they weren’t going backwards so we’d still like to understand whether
a chemical reaction could ever go backwards now to do that we first of all have
to ask why does a chemical reaction happen at all why the chemical reactions happen in the first place but to understand that we’re gonna
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 gonna set fire to the baloon
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
can you put your hand up if you enjoyed that demonstration its quite a few can you put your hand up
if you’d like to see a slightly bigger one okay that’s everybody
alright come on Chris okay now the last
balloon may have quite a pop this one is going to make an even
louder pop quite a loud bang in fact I’m standing quite close to this so
I’m gonna wear my ear defenders 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 would have
noticed in that reaction that energy was released clearly so we’ve got a lot of noise we saw the flame we saw the lights I could feel the heat and probably in the front row could as well so energy was released in that
reaction so what’s happening is that the starting material
the hydrogen and oxygen were in a state
of high energy and as a result of the reaction they’ve
moved 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 is given out in the form of that bang that’s a the heat and the light and the sound and
so on so maybe that’s why chemical reactions happen may be chemical reactions happen because the
chemicals move from a state of high-energy to a 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 down hill from a state of high energy to a state of low energy so maybe that’s how
chemical reactions work if it is how 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 up hill that’s not gonna 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 in
the form a bang we saw a little bit light being given off there
in the form of that flame and I want to show you reaction that
gives off a great deal of lights it’s the reaction of a rather special
element it’s called phosphorous and the word phosphorus comes from the Greek
it means that 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 larger 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 gonna burn quite a big
chunk of white phosphorus inside this flask, and to make it burn really
well, we’re gonna fill the flask with pure oxygen now in order to fill the flask
with pure oxygen we’re going to use liquid oxygen; and we’re gonna
make the liquid oxygen by starting from another
liquefied gas – liquid nitrogen so in this vacuum
flask I have some liquid nitrogen it’s a, a colorless
liquid – it looks pretty much like water but it’s at a very low temperature. It’s at – 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 -196 degrees centigrade and pour it into some pretty
much boiling water okay and and this is what happens there’s no real point in 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 this 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 liquid itself and so this
vacuum flask contains liquid oxygen i just want to show you one interesting
thing about to 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; and the air of course is completely transparent and yet oxygen when it becomes a
liquid turns this lovely blue color okay so we’re going to use this
liquid oxygen then to fill this flask with
oxygen. So I’m going to pour this in and we’ll add a bit more for good
measure should be enough ok and so the oxygen the liquid oxygen is warming up as it touches the flask
and it’s evaporating it’s turning into oxygen gas and as 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 flask and filling
the flask with oxygen just to help that along a
bit just gonna swirl this around okay you can see a little bit of liquid oxygen there that lovely blue
color sloshing around in the bottom of this flask so that 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 fill it with oxygen
that way but I think this was more fun okay while that last little bit is evaporating the next thing we’re going to do is to get some phosphorous there are two kinds of phosphorus red
phosphorus 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 a bench it will actually catch fire after a few
minutes and so we store it under water So I’m gonna fetch out this piece of white phosphorous and we’re going to put
it in a little spoon that’s suspended from
the lid of the flask You can see the phosphorous 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
phosphorous just to get things going and as a as soon as the phosphorous
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 that’s being given out it’s a very vigorous reaction the flask is filling with
oxides of phosphorous so thats white phosphorus
the bearer of light 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 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 disulfide. I’m gonna
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 we’ll just bring the
lights down first So you’ve seen a couple 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 fifty-pound note as an example of
combustion so let me soak the fifty pound notes
in some flammable liquid and then we’ll set it on fire this
is a this is my fifty pound notes its brand new, and there
it is on fire the flames have gone out but the fifty
pound notes I’m pleased to say is entirely intact. I’m very pleased about that Now the reason that the fifty-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 fifty pound note – it
absorbs heat, and it stopped 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 I’ve got here three fire extinguishers based on different
kinds of Chemistry Now it would be very surprising wouldn’t it if we could use a fire
extinguisher not to put out a fire it to make a fire worse. It would be really
surprising if we could use a fire extinguisher to start a fire okay let’s look at the first
kinda fire extinguisher so this is called a water fire
extinguisher it contains water under pressure when you let extinguisher
off the water comes out at the hose you soak the fire and you put the fire
out. Now if I let that off in here it would just flood the lecture theatre so we do
something else that’s 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 we can you’re careful or you’re wishful so this is just like that
water fire extinguisher it squirts a jet of 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 are very quick lets give a hand for our volunteer please and what’s your name yeah
Ciara, right Ciara ifyou like to put on these safety goggles these are special
safety goggles because they are tinted nice trendy shades
all right and what you are going to do is
to squirt the water pistol at the little metal dish. Can you see
that on the little stand there and that dish contains a
mixture of silver nitrate and finally padded magnesium and if you
get a little bit of water to land on it we’ll see if that can start a fire now because
this contains magnesium is going to produce a very
bright light so my suggestion 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 can hit it in the water so that’s we’ve given you these special
goggles all right so of you go see if you could get a little bit water into that dish well done but thank
you very much okay so that was the first time a
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 kinda fire extinguisher it has
got a carbon dioxide fire extinguisher and it contains
liquid carbon dioxide under very high pressure
so just I pull out the pin and point the nozzle up
we’ll just set this off and okay so you can see the liquid carbon
dioxide and a very high pressure comes out through the nozzle it turns
into a gas now carbon dioxide is often one of the main results of combustion
it’s something light wood or paper is burning the carbon reacts with the oxygen in
the air to produce carbon dioxide to the carbon dioxide is the
end product of combustion that’s why it is good for putting out fires
so we use the carbon dioxide fire extinguisher to smother a fire
exclude the air and therefore exclude the oxygen
and then the fire goes at to be a bit odd if using a fire extinguisher like this would
actually make the fireworse 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 little
bit earlier in the lecture this is a block of dry ice and again
we are going to use magnesium so I have some
magnesium metal here and its gonna make a
little pile in a little trough that we’ve cut inside
the block I’m going to set fire to the magnesium
and once its 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 it’s not putting
the fire out it’s actually supporting combustion giving out this beautiful light the white
smoke you see is magnesium oxide this is the sort of stuff that’s used
in the indigestion tablets that kind of thing I would’nt 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
kinda fire extinguisher and that’s this one this
is called a dry powder fire extinguisher it contains
a powder this pressurized when we set this off the
powder comes out of the hose and we can squirt at the fire and put
the fire out now these are actually extremely good fire extinguishers you have an
extinguisher in your kitchen one in your car is probably a dry
powder extinguisher and these extinguishes usually contain
something like sodium or potassium carbonate or sodium or potassium bicarbonate
they’re very effective extinguishers they are good for
dealing with all kinds of fire and it would be very surprising if using the
powder out of one of those that actually make combustion faster
on make it worse well i have to say can in this spoon we have a gram of
commercial gun powder it’s made from a mixture of three ingredients saltpeter ( chemical name is potassium nitrate ) and that act’s as a source of concentrated
oxygen we call that an oxidizer it contains charcoal
which acts as the fuel that burns in the oxygen released
by the potassium nitrate and it contains sulfur and
the sulfur is there to aid combustions make the gun powder burn more easily what would happen if
we took gun powder and instead of using charcoal
which is the main fuel we use some of the powder from a
fire extinguisher so this seems pretty odd we gonna take away the
main fuel from the Gunpowder and we are gonna replace it with something
that’s used in a fire extinguisher we are gonna use potassium carbonate for this so if we 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 black powder and in this spoon
we have a gram of yellow powder now what I’m gonna 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 a yellow powder now gunpowder when it burns in
the open doesn’t make a bang it just burns with the Puff in a little cloud
of smoke so we are not expecting the gun powder to make a bang
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 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 but it will ignite we’ll see a puff of
smoke the other part 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 as a result of being warmed up and at some point that
new mixture of chemicals should give rise to a little
explosion and the gun powder gives a beautiful smoke ring okay so that’s some of the science of
combustion and that’s how the powde the powder from 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 I said this is a very interesting
question let me show you a fascinating reaction so in this beaker is a colorless liquid
I’m going to add a second colorless
liquid it remains colorless I’m gonna add some
yellow liquid and it turned orange and add a little bit of red liquid and it goes sort of green color kind of muddy color now in a minute
or so that muddy mess will fade away we’d be able to see the color of the
solution what I want you to do with to watch the color of this solution as it changes now the rather interesting story behind this reaction was first discovered in
about 1951 by a russian chemist called Boris Belousov 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 beaker and he discovered some very interesting
color changes any 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 you can see that muddy
color is fading and we’ve now got got a green solution the solution
is not gradually turning blue remember that it started at
Green and it’s turned blue I Borissov tried to sum it
all by the late in chemical reaction sort of like a reaction
that goes backwards and people thought that reaction’s
didn’t do that sort of thing so you 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 not turn from
blue to red and green to do Reds so missile had his paper rejected
3 send it to another journal and they did the same thing they
rejected as well because they thought democrats it just shouldn’t
behave like this must be something wrong so you got
pretty depressed about this if I got so depressed that he gave
up being a scientist a discovery was so difficult and and about ten years later
a Stevens have chemistry zabinski that since the
Russian student discovered status of notes not stand up
to blues has turned grade all rights so remember that sequence
a green for a little while then blew that it went Reds them but
simply briefly now it screened so that the tin CE discovered the
littles notes and he recreated this experiment and he was able to is
published the conference in Vienna and then the whole world near back
sittin’ again quite a sensation they’ve got very excited about
these kinds of reactions cases gone back to play it is now turning back
to read we’ll keep going through that sequence of colors so it seems as if we have a
reaction sorta goes back with released it goes round in a cycle so
most people started to study these reactions and they came
up with other kinds all oscillating reactions 2012 show you
one that has quite a nice story to it because this is discovered not by
professional chemists the by a couple earth schoolteachers and
their names were Briggs and Russia and then working a high
school in San Francisco and they were using the school
chemistry labs after hours and they discovered a different
kind all oscillating reaction so again I have a clear liquids
I had a second clear liquid and a third clear
liquid that turns amber to keep watching turns blue radar late so there’s a
little bit like the clock reaction the same thing erection
something starts and I attained at this time it doesn’t stay
play is going clear again so it’s become clear that’s going back to amber to keep watching
actively work and turns to blue again okay so those are two
oscillating chemical reactions just seems as if we found a chemical
reaction the does actually go backwards but really that isn’t what’s happening
it’s not like a ball rolling downhill and then change its mind a rolling back up hill again
it’s more like a ball going down a so to the 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 we could watch these oscillations happening but after 10 or 20 minutes
they will come to a stop and that’s because the chemicals have
been used up so we haven’t really found reaction yet that can go backwards
so does that mean that of theory of chemical reactions is
correct member of theory is the chemical reactions
like a ball rolling downhill the chemicals go from high-energy to
low-energy and they give that back energy difference in the fall
people light or sound or whatever well let’s look at this reaction
this interaction between two powders so in the beaker’s some barium
hydroxide it’s a white powder I’ve got a block of wood I
was gonna put some water on the surface the what makes a
puddle I’m gonna stand the beaker in the puddle and then in
this peak and this flask I have some ammonium
chloride I’m at the ammonium chloride to
the the barium hydroxide and I’m gonna stare
using this probe which is attached to this the moment
that this digital thermometer things in the temperature
there is about 20 degrees let me start to mix the prior to us
together and we’ll see what happens to the temperature so the temperatures falling
very quickly well below 10 degrees now and they took it has just gone negative
this is now the low note the grace so it’s a -7 degrees so the
temperatures falling very rapidly the other thing that’s happened
is that it’s turned from a solid into a liquid does not come
with a slushie white liquid the temperatures down to -15 degrees so
well below the freezing point of water i remember i stupid in
little puddle of water so what should have happened
is that water should a frozen never got frozen it
to the block it would so that’s pretty strange
because that’s the reaction that didn’t give an insanity
it’s a reaction took in energy it actually took in heat from the
surroundings and that’s why the surrounding such
as the thermometer dropped in temperature
so that’s a bit like putting the ball on a slope and
seeing the ball roll up hill but it shouldn’t happen to
this array strange reaction it means that all theory
of wine 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 you know theory all had chemistry happens went
to illustrate this with the little computer game we got
here a hundred discs and each disc is yellow
on one side it’s red on the other and the ball
down the right answer side show see the proportion of this
coochie yellow now starts at the mall of as Yellow and let’s see what
happens when we run little simulation so that a
hundred times a second the computer is choosing
a desk and its deciding either to keep it the same color or to
flip it over and you can see on the right hand side the proportion upgrade and yellow now we
started off with all the disks yellow very quickly we’ve got to state
where about half of them Red in about half the
yellow let’s try again at this time we can set them all to
read we can run the little simulation they start of all rate
very quickly they come to a state where about half as the
reading about half of the magellan so me to say this is
the think that we started the discs off in a very ordered
state they were all the same color and as the simulation run the level is disorder increased it went from a and ordered
state two more random States and this is such an important idea given
a special name we call the degree of disorder entropy we say the entropy
tends to increase with time we start of the things recorded
and they became very disordered and the reason this happens very simple
is because there’s only one way for the disturb your yellow there are lots and lots and lots of ways
for the DS the beast the roughly half yellow and of bread and so it’s just simply can sing
the number of different ways have arranging these discs that causes the
dais to go from an ordered States the disordered state now
you might think well well hang on a moment
if we wait long enough sooner or later by chance although
this will become yellow again so the system would then have gone from
the disordered stay tuned ordered States now you’re absolutely right
you have to wait a long time this is doing about a hundred flip to
second if we did a trillion flips the second you still have to wait longer
in the age of the universe on average before you see
them or yellow again so it’s almost certain that the world will move
from an altered states to disordered state I’ve got a couple other
teenage boys and their bedrooms provide a perfect
illustration of this at if i tidy their bedrooms everything is
very or didn’t come back the next day is almost certain to be a highly
disordered state without input from me it will never gain from being disordered
to being ordered so that’s the idea entropy entry fee increases and that
can drive a chemical reaction so let’s think about a solid in a solid the atoms or molecules
are arranged in nicely rose they’re very order in so
the crystal lattice in a liquid the molecules can move around
not in fixed positions anymore so this is a more
disordered state in a solid and a gas is even more
disordered because the atoms or molecules are free to move
around they can fill the container so as we go from solid to
liquid to gas the entropy all the disorder increases up sarra to
things that can drive chemical reactions is the ball rolling downhill
effects the decrease in energy all there is the
increase in entropy the teenager bedroom
effect this reaction is being driven by that increase
in entropy is gone from a solid to a liquid and that increase
in entropy is so big the overcomes the fact he actually
has two increase the energy that reaction to happen that
reaction happens spontaneously let’s draws energy in from the
environment and cools its environment and 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 I find a chemical reaction
that goes backwards well to help this find
this I’m going to use the word curious in a different
sense we’ve used curious to the strange or surprising or unexpected the curious
can also refer to desire2learn to curiosity I’m gonna
tell you a story about curiosity in a a young chemist so
easily with ira rents in and as an adult he became
very famous he founded the chemistry department at John Hopkins
University and he discovered the first official sweetener let’s call saccharine but
as a teenager he was curious about chemistry and used
to do some little experiments I’m good telly 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 gonna show you their action
the reactions gonna happen in this flask in this cylinder at the top
we have some nitric acid and the flask we have
copper now the copper as you for reasons you’ll see in
a moment in the former a coil account is the Morton a penny or tea
party piece because they’re actually made of steel just a thin coating of copper
so gonna an old-fashioned penny here this was made in there 1945 this actually made of solid copper
so we put one of these pennies into the flask and we gonna do this
reaction in a sealed environment in a sealed flask any fumes that a pretty to be led away
through this cheap and absorbed in this sodium hydroxide for reasons that will
become apparent in a moment okay so this is the
story although I Ramson while reading a textbook of Chemistry
I came across the statement nitric acid acts upon copper I was getting tired reading such
absurd stuff and I determined to see what this meant copper
was more or less familiar to me for copper sense with that in use I’d
seen a bottle marked nitric acid on a table in the doctor’s office
well I was then doing time I did not know its
peculiarities was getting on likely to learn the spirit
of adventure was upon me having nitric acid and
copper I had only to learn what the word act upon meant then the statement nitric
acid acts upon copper would be something
more the mere words all was still
interested knowledge I was even willing to sacrifice one
of the few copper sense that 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 a prepared to make an observation so let’s at the nitric acid to the copper and see what happens I think you can say that quite a
vigorous reaction is taking place to the green liquid
bubbling away fumes are coming off I let’s
continue with the story but what was this wonderful
thing which I beheld the saint was already changed
there was no small change either a greenish blue liquid phoned
in fumed over the scent and over the table the area 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 attacks upon fingers the pain led to another
unpremeditated experiment I drew my fingers across my trousers
another fact was discovered nitric acid acts upon tries as taking everything
into consideration that was probably the most
impressive experiment and relatively probably the
most costly experiment I never performed I tell
it 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 a faction plainly the only way
to learn about it was to see its results
to experiment to work in the laboratory so that the
reaction of nitric acid with copper which produce these dark
brown fumes that 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 SEO apparatus but nice and I oxide is a material that
can help us understand this question about whether a chemical
reaction can go backwards so in these cubes we have equal amounts all nitrogen dioxide
what I’m gonna do is to take one of the tubes
and to place it in iced water that it will cool down and the
other cheap a little place in hot water to heat it up
so come back in a moment and see if they’re changed in any
way let’s have a little look at the chemistry that’s
going on inside those tubes and nitrogen dioxide
has a molecule which consists of one at
Earth nitrogen and two atoms oxygen if we have two molecules nitrogen dioxide they can react
together to form one molecule all another oxides of nitrogen
called dummy nitrogen tetroxide that process
releases energy when that extra nitrogen 19 bond
is formed it gives out energy so that’s like the ball rolling
downhill the ball rolling downhill want the notion dioxide come together
performed I nitrogen tetroxide but the domination tetroxide can split up the molecule can split in half if two molecules
of nitrogen dioxide because for every molecule diana ichton tetroxide we
get two molecules Nigerian 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 a
driving this reaction is to love opposite directions what happens is that the reaction
actually goes in both directions at the same time it
reaches a sort of balance we call it an equilibrium where there
is some much in by upside present and some dynamited and
tetroxide present and the relative proportions that these
depends upon the temperature so if we increase the temperature we put energy
into the system that’s like pushing the ball up hill we go from right to left
if we cool system banned then conversely we go from left
to right so that’s the prediction and we can test the prediction because nineties and dioxide is this
dark brown gas that you see in the flask here but die nice in tetroxide is colorless so we
go back to a cubes this is the cheap that
was in the cold water and you can see that
it’s become a pale kala this is the cheap that was in the hot
water I just put the side by side you can see that heating up this
gas has made it dark brown and contains more nitrogen
dioxide rest cooling it done has made it at less
dark it contains more die nitrogen tetroxide and
just two check of theory what we can do is we can take
the hockey if the doc to you and place it into the cold
war stop and then the the coach you which is the pale
kala we can place that in hot water will come back and have a look at those
in a moment we’ll see if they swapped places the case that really brings us
towards the end of the lecture want to do is just
to show you one more curiosity and it concerns a
rather interesting and unusual element and this elements was
discovered in a mine in a outside a little time court Turkey
which is near Stockholm in Sweden and they have been extracting minerals
from the mine and they found a mineral it seemed rather peculiar
they couldn’t understand what it contained insulate realize
that it contained a new element this is so the beginning of the
eighteenth century and those that is if you discovered a new element
you got to choose its name and they decided to name the element
after the town to the turkey this element is called yttrium
what rather interesting is that this mineral contain
not just one new element but they found out to
contain four developments and so they decided to name all four
elements after the time to the turbine so these four elements
accord yttrium ytterbium erbium and terbium which is a a little bit confusing I think
we can look at the thirsty these yttrium now yttrium can be used to make a compound and I
have some at the compound here it’s called yttrium
barium copper oxide that just a hard black
love ceramic material when you to do is
to put into some liquid nitrogen and so that the tree in barium copper
oxide is now being cool down to minus a hundred ninety-six degrees but 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 gonna cover this in liquid nitrogen so that too can be cooling down now at room temperature this
material isn’t very remarkable but when he gets officially cold has a
very interesting a very strange property becomes what we call
a superconductor now superconductor is a material that
is lost all its electrical resistance and material which has 0
electrical resistance has the property that it
can repel a magnetic field so this rig the ring made of
steel and it’s covered in little magnets very strong magnets I alternates
North Pole South Pole North Pole and so on and in a minute when this is
cool down on we get to see if thats yttrium
barium copper oxide can repel the magnetic field
produced by these magnets this just takes a a moment
or two to cool down so we’re looking here I can see
their boiling away very vigorously that means the the ceramic materials
giving up its heats to the liquid nitrogen is boiling
liquid nitrogen away and and cooling down in the process
essentially I’m just waiting for the boiling to stop when it stops boiling that
means the ceramic material has reached the same temperatures the
liquid nitrogen so limit minus a hundred ninety-six degrees okay so let’s touch the Sun
then let’s see if this can repel magnetic field okay so this is actually
quite a special kind of superconductors what we call the type to
see picking up to and that means that as well as repelling magnetic field you can
also track magnetic field remember I’ve got another wanna be sitting
inside this policy link-up and underneath is a still at that
and on the top of the cylinder is a very strong magnet now the field from that night that
was already passing through the ceramic material before
I added the liquid nitrogen site now cool it down should
have become a superconductor and hopefully it will have traps that
magnetic field so should still be gripping onto that field that means I should be able to take
away the support from this cylinder by the way on the outside the cylinder
we’ve put the logo for the International Year of Chemistry 2011 has been a year-long
celebration around the world off with the likes of Chemistry and
the importance of Chemistry for our everyday lives I thought it would
be a nice way to just mark the occasion I think this is cool
down as sunday tea see if I can lower
this very carefully the okay well thank you very much that that
pretty much brings us to the end of the lecture just before we wrap up I’m I thought
we would we finish with the with a rather nice demo but
just before we do as 12 ask you to join me in thanking somebody
please put a lot of effort into helping me prepare and
deliver this lecture and thats crisp black stallion okay just before we finish I thought we
take a look at this block of dry ice if you remember we burn some magnesium
inside this block is dry ice so the chemistry here was that the
magnesium reacted with carbon dioxide to produce magnesium oxide and carbon
and if you look at the surface if this we can see that it’s coated in
a white powder and that’s the the magnesium oxide
if we dig down inside the black had a is the
carbon and then finally we swaps those two teams
that we put the dark to you inside the iced water we put the
light-colored cheap in the hot water we can say they have indeed
swapped places so the cheap was dark has been cool
down has become lights and the like quality has been heated up
it’s become dark so we have the role other curious conclusion the chemical
reactions can go forwards and backwards at the same time alright
well that really is the end of the lecture but I thought would have just one
more demonstration to finish and I thought what
we do is two repeats one of the earlier demonstrations
it’s the demonstration all the reaction between nitric
oxide and carbon by sulfide I thought we did on a slightly
bigger scale so chris is bringing on a cube of nitric oxide some good add the carbon dice 05 began
chris is going to mix these together once they thoroughly mixed will set fire to the
end of the queue all rights and will put the light stand for
this might say thank you will for coming we go old its

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