so this is another place where you might
find co2 every day at work or maybe even
at home in the kitchen we use it in fire
extinguishers now if we shake this
bottle we can hear that there's some
liquid slopping around inside and that's
liquefied co2 so co2 is useful as an
extinguisher for fires because it
doesn't sustain combustion it's non
flammable so if there is a fire we
squirt co2 which is quite dense it
blankets over the fire excludes oxygen
and puts the fire out so let's see some
more gaseous co2 carbon dioxide is
really interesting molecule it's very
simple this has carbon here with two
oxygen atoms one on each side so it's
just three atoms in a row today what
we're going to do is we're going to
explore the three state of matter
looking at a single molecule and we're
going to use co2 so at standard
temperature and pressure co2 is a gas
and actually I'm breathing it out so
here we go we make some co2 the molecule
has many interesting properties one of
them is that most gases when you
compress them will liquefy and form a
liquid and then if you cool the liquid
down it will freeze what is interesting
about common dioxide is that you cannot
get the liquid at atmospheric pressure
so you can get all sorts of little
containers that contain liquid co2 but
if you open them release the pressure
the co2 converts into a solid so called
dry ice which is very cold but goes
straight from the solid to the gas
without melting so hopefully today we're
going to look at co2 at a gas co2 is a
liquid and co2 is a solid and perhaps
we'll look at some reactions as well
there are double bonds between the
carbon and the oxygen
because each oxygen normally wants to be
bonded to two atoms but here you can see
it's only bonded to one carbon so it has
a double bond two bonds together
so this is where we're going to get our
co2 from it's a rather large cylinder so
on on the cylinder we have a device
called a regulator which you can see
here now what that does is it limits the
pressure of the gas that we get out into
our pipe so this is really for safety
because the pressure inside the cylinder
is a lot higher than the pressure that
we require in our reactor or inside our
balloon so here we have a balloon a
rather strange button so now you can see
we've we've collected a balloon full of
carbon dioxide and as you can see it's a
rather nice balloon it's the same as any
other balloon what do you think what a
blue sea you do so see you too is a gas
co2 is one of my favorite molecules
because co2 is a liquid or a highly
compressed gas will dissolve chemicals
just in the same way as petrol or other
organic liquids will dissolve them and
so you can use carbon dioxide as a
solvent for chemical reactions and this
highly compressed gas the so called
supercritical fluid is something that
both I and Pete licensed who does lots
of our demonstrations we've done a lot
of research on this most people when
they think of co2 they think of as a gas
but if you you take that gas and you
pressurize that gas you squeeze it if
you put it into a bottle perhaps or a
container and you squeeze it the gas
molecules are brought closer and closer
and closer and closer together until
eventually they will condense and form a
liquid phase now what we've done with
our experiment is we've taken the co2
and we've connected it to a special
piece of apparatus which you can see
it's made out of things like stainless
steel and technical instrumentation but
the key thing about this apparatus is
that unlike a normal stainless steel
vessel we have a window inside this
vessel which is able to maintain
pressure it's able to take the stresses
because of the pressure trying to
push against the atmosphere and its
really good for chemical reactions and
again by using carbon dioxide as a
solvent you can avoid having to use and
products made from petroleum which might
otherwise use up and deplete the
petroleum wares carbon dioxide we have
more than we know what to do with from
various industrial processes so it is
available really quite widely so the
window that you're looking through in
this experiment is is sapphire I must be
expensive
hell yeah they're about the front window
in this cell is approximately eight
hundred pounds and the rear window the
one which moves is about fourteen
hundred pounds so quite expensive and
but but absolutely critical for this
experiment and if as is proposed co2 is
captured from power stations there's
going to be a huge amount of co2 and if
you can use that for chemical reactions
for extracting materials one of the main
commercial applications of high-pressure
come dioxide at the moment is for
decaffeinated coffee many years ago
coffee was decaffeinated using dry
cleaning fluids which can leave all
sorts of residues in the coffee beans
people may not want to drink the coffee
but caffeine is soluble in co2 and most
of the other components of coffee beans
are not so you can extract the caffeine
from green coffee beans so you get
decaffeinated coffee and the co2 leaves
no residues at all and then by reducing
the pressure or washing the co2 with
water you can get the caffeine out and
you can sell it to people to put in
their soft drinks now Neil's been really
active and he's ordered in a special
piece of co2 for us which he's going to
get out of the box now
so um what we thought to do today is
perhaps a little bit of an ice sculpting
so we're going to cut the co2 and a half
and make a reaction vessel okay and then
we're going to do a nice chemical
reaction with it
so here Neil's cutting the the co2 now
with a saw and this is the typical saw
that you might find in a hardware shop
or a do-it-yourself shop so one of the
advantages of sawing this material is
that you don't have to clean up the
sawdust because it just evaporates