So our reaction’s ready. Now all we need
again is a little bit of water just to start it off. So we’re here today and we’ve come back
after hours because we need to use this room for a long
period of time because we’re going to do something quite exciting. Because Brady’s
bought another camera which you can see he’s setup over
there and we’re going to use that second camera to capture
one second of film every minute for maybe two or three hours and we’re going to do
some time lapse. Something I’ve seen on TV with like flowers
opening or plants growing but never with chemistry developing. Silver is one of the few metallic elements
that occurs naturally as the metal in nature. So that if you’re
lucky you can wander around and find lumps of silver lying around on the ground. And
this is how, in ancient times, silver was discovered so it
has been known for thousands if not tens of thousands of
years. Gold is somewhat similar and also copper. But most other metals combine too easily with
oxygen or other elements so you don’t find them
naturally. So I thought what we’d do today is through
a competition reaction and that competition reaction is based
on something called the reactivity series of metals. So we’re going to compare the
reactivity of two metals. It’s a bit like a game of football.
We’re going to give one of those metals the football and in this
case it’s another component or another salt component, nitrate. So the two metals that
are going to be competing for the nitrate are silver and copper.
And really these are related by something called the
reactivity series. One of these metals is going to win, I know that and I hope we’ll
find it during this video. Silver had a particular use in photography
and in the old days when people used photographic film the
black colour that you saw on developed negatives is in fact silver. A photographic film consists
of a layer of silver bromide or sometimes silver iodide
and when the light shines on it the light just starts a tiny
amount of reaction making silver and then when you put it in the developing solution
the catalytic amount of silver that you’ve produced causes
a big reaction and you make a large amount of silver. And
so you get this black colour which then you can print as pictures. So on the bench I’ve got a small beaker
or an Erlenmeyer flask, as we chemists call it, which is full of
deionised water. So we’ve passed the water through a machine which has taken out all
of the other ions so that they can’t play around with the
competition reaction that we want to start today. Firstly, I’m going
to start off by giving the prize of the competition to silver. So here I’ve got a sample of
silver nitrate. It’s sensitive to light so I can’t leave it out
on the bench very often. So now what I want to do, I’m going to
put some into the water to make a silver nitrate solution. So I want to make sure that there’s
plenty in there so that it’s saturated. Now we’ve
got to put in the competitor. So what we’re going to do, we’re
going to take some copper, copper metal. And this is just a sample of wire which I’ve
rubbed with some wire wool just to make it sort of nice and
shiny. And now all I’m going to do is dangle it into the silver
nitrate. Then it’s going to start to compete for the nitrate and we’ll see what happens. So Brady’s started the recording and I think
the best thing for us to do is to go away and do something a
little bit more exciting and come back and have a look in an hour. Silver has become quite popular recently as
a potential new way of making things anti-bacterial: killing
bacteria. So now we’re going to make some flash powder
and the flash powder we’re going to make today is a
two component mixture. It’s very finely ground magnesium and the second component
is ground silver nitrate, solid OK. So we take these two components
and we mix the two together very intimately and
Neil’s just weighing the materials out right now. So we’re going to put the magnesium
and the silver nitrate, the two powders, together into a
small plastic container here. We’re going to mix them very,
very carefully and then we’re going to see what happens when we initiate a chemical reaction. For hundreds of years people have used silver
spoons. Partly, I think, because silver is quite easy to
make but also because the silver does have properties that kill bacteria so a silver
spoon is less likely to get harmful bacteria on it than if you have
one that’s made out of wood or horn of a cow or something
like that. So we’re mixing these very carefully, in
the fume hood, just in case the chemistry starts before we want
it to. And in recent times people have started making
very, very fine particles of silver, so called nanoparticles, which can exist in solutions.
So here I’ve got a solution of silver nanoparticles. You can
see it doesn’t look silver it looks a bit yellow actually and you can tell that it’s
got particles in it because, if I can find a torch… So here we’ve got
particles and you can see the particles better if we shine a light
through it and if you look at the light you can see that there is a cone of light that
looks rather like the headlights of a car in fog. And this is an
effect that’s called the Tyndall Cone which indicates that there
are very, very tiny particles suspended in the solution. So this is not silver dissolved
in the water but actually very tiny particles. So let’s start the reaction, just with a
little bit of water. Wow! I think we should do it again though. Yeah!
LAUGHTER People are now using the silver nanoparticles
for all sorts of purposes. Here you can see that they’ve
been put onto some sort of plastic and you can now buy socks which have silver nanoparticles
on them which are claimed to kill the bacteria that
make your feet smell. So we’re going to repeat the reaction. B-B-B-B…
SQUAWCKS That’s going to come out somewhere isn’t
it? Silver will conduct electricity, it will also
conduct heat. If you’ve ever tried stirring tea with a silver spoon
it gets very hot, you tend to drop it. It also conducts electricity well. So we’re going to repeat the reaction so
that you can see it again, because that was really fast. This
time we’re going to do it on a glass dish so you can see it a bit better. We’ll pour
out a small amount. LAUGHTER So our reaction’s ready. Now all we need
again is a little bit of water just to start it off. Did you catch that? I managed to close my eyes this time(!) During the Second World War, when the US government
was involved in enriching uranium as part of
the Manhattan Project they needed an enormous amount of wire to make magnets. And so a huge
amount of silver was taken from the US treasury where it was stored as silver to give value
to the US dollar and was turned into wires to make magnets.
And I believe that the silver was never returned or at
least it wasn’t returned at the end of the war as was promised. Well, I’ve managed to fill maybe one minute’s
worth of time by now maybe two because we’ve been
away about two hours. So we’re going to go back and have a look at the flask to see
if there are any changes. If you remember when we left it was
a nice clear solution of silver nitrate with some copper
wire which was just immersed inside. So let’s go and have a look. There’s been big changes in our flask! So
if you look carefully you can see now that the copper wire
itself is covered in very, very sharp crystals of silver which have basically become deposited
on the surface. Copper has now won this chemical
reaction. It’s now going into the solution; it’s taking the salt
element and precipitating solid silver crystals. So if you look carefully, you can see that
the colour of the solution has changed. It was colourless, now
it’s blue which tells me there is another ion, copper, in the
solution.
Actually, all the silver in the calutrons were indeed returned to the treasury. No one's gonna let that much precious metal just walk away.