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 goes
okay 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