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.