Extracting Metals (GCSE Chemistry)


Uploaded by freeeschool on 04.09.2012

Transcript:
GCSE Chemistry – Extracting Metals
Hello and welcome to this video about Extracting Metals. We are going to look at the processes
involved and how metals can be extracted from the earth.
An overall view of this to start us off is something like this. We have the metal ore
and the metal ore often contains some impurities. In the first stage, what we do is we can concentrate
the ore by removing some of those impurities. So we concentrate the ore and then with the
concentrated ore which has a higher proportion of metal in it, we can carry out some chemical
reactions. Through the process of chemical reaction, we can then have the pure metal.
This chemical reaction over here usually involves removing oxygen. The reason for that is the
metal over here is usually metal oxide. The metal is in the form of an oxide. It is not
usable as a metal as such, but once we remove the oxygen from the metal oxide, it then becomes
a pure metal so that we can use that for whatever purpose we want. This is an overall view of
how this process works.
Let’s have a look at a particular example. Before we do that, let’s have a look at
this list of metals here called The Reactivity Series. Now, you do need to be aware that
this is unlikely that you are going to be asked to memorize it, but certainly, you will
be asked to use the list.
Basically, what we have here is the list of metals and their order and in the order of
their reactivity. In other words, we have the most reactive metal at the top and the
further down we go, the less reactive the metals. The least reactive metal is in the
bottom. In this list, the least reactive metal is gold and the most reactive is potassium.
I’ve put in carbon here. Carbon is not a metal, but I’ve put it in the list to show
how reactive it is compared to the metals because we often use carbon to extract metals
from their ores, but it depends where the metal is on this list, whether we can use
carbon or not. I will explain this further.
If we take the example of say, Iron ore, this is a rough diagram of iron ore or iron oxide.
If we react it with carbon, a very interesting thing happens. It happens based on this list
over here. Now, you can see in this list, in the Reactivity Series list, you can see
that carbon is higher than iron in the list. So that means that carbon is more reactive
than the iron. What that tends to do is because it is more reactive, it will remove this oxide,
this oxygen away from the iron. So what we are left with as a result of this is you will
have the iron metal and you have the carbon reacting with oxygen and that actually produces
carbon dioxide gas. Because carbon is more reactive than iron, it removes the oxide away
from the iron, leaving the iron in its pure form. If you write that as a chemical equation,
it would look like this: we would have iron oxide plus carbon will give you iron plus
carbon dioxide and this is the reaction that we used. It is actually using something called
the “blast furnace” which we will not go into now. But this is a reaction that we
use to remove oxygen from iron oxide to give us pure iron.
Now, let’s have a look at another example. An example that we are going to look at now
is Aluminium oxide. Aluminium oxide produces the metal aluminium which is very useful but
we have to remove the oxygen from it first. So if we then react it with carbon or by heating
it with carbon, is it possible to react and remove the oxygen and therefore get the aluminium?
Well, let’s have a look at our list over here. We can see that the aluminium is more
reactive than the carbon. So whereas carbon was more reactive than iron in the first example,
in this example, the aluminium is more reactive than the carbon. That means that it is actually
going to hold on to the oxygen. The aluminium is going to hold on to the oxygen and as a
result of this reaction, is we are still going to have the aluminium oxide and we are still
going to have the carbon. In actual fact, there is not going to be a reaction here.
Therefore, we are not going to be able to extract the aluminium, but that’s not the
end of it because aluminium metal is an important metal and it is a very useful metal. We have
to use a different strategy. What we have to do is to heat the aluminium oxide which
will melt it and we use a process called “electrolysis”. So metal up this end of the pure reactivity
series tend to require electrolysis to remove them, but what you have to remember is electrolysis
requires a lot of energy which makes it more expensive. So the method for extracting metals
up the top end here is possibly and probably electrolysis, but you have to remember that
it requires more energy. It makes the process more expensive and therefore, makes the metal
more expensive and overall, the cost of aluminium is higher simply because it takes more energy
and energy-hungry process.
So overall, that’s the extraction of metal. One last thing probably worth mentioning is
that the metals down this end are very unreactive and in fact, something like gold is so unreactive,
it won’t react with anything in the environment. It won’t produce gold oxide. It won’t
react with oxygen. So it can just be found what we call “native” in the ground as
the element itself. It doesn’t need any chemical reactions to extract it. That’s
it for now, I hope you enjoyed and I’ll see you again soon.
[end of audio – 6:30] GCSE Chemistry – Extracting Metals Page…1