Lesson video

Hello, I am Mrs. Adcock and welcome to today's lesson on extraction of metals by reduction.

We are going to be looking at how we extract different metals from their ores.

Today's lesson outcome is I can explain how carbon can extract some metals from metal oxides by heating.

Some of the keywords we will be covering in today's lesson include metal oxide, oxidation, reduction, ore, and redox reaction.

Here you can see each of those keywords written in a sentence.

It'd be a good idea to pause the video now and read through those sentences.

You might even like to make some notes so that you can refer back to them later in the lesson if needed.

Today's lesson on extraction of metals by reduction is split into three main parts.

First of all, we are going to be looking at metal oxides.

Then we are going to look at extraction of metals, and finally, we are going to look at reduction by carbon.

Let's get started on the first part of our lesson on metal oxides.

Metals react with oxygen to produce metal oxides.

A metal oxide is a compound that contains metal and oxygen atoms chemically bonded together.

The word equation for this reaction is metals reacting with oxygen to produce metal oxides.

An example would be tin, that's our metal, reacting with oxygen, and this would produce the metal oxide known as tin oxide.

Here, we can see a balanced symbol equation for this reaction.

We've got tin, reacting with oxygen to produce tin oxide, which has the molecular formula SnO2.

What is the product of a reaction between calcium and oxygen? Will calcium and oxygen react together to produce, A, carbon dioxide, B, calcium oxide, C, hydrogen, or D, calcium carbonate? The correct answer is B, calcium oxide.

So well done if you identified that as the correct product from a reaction between calcium and oxygen.

The reaction between a metal and oxygen to produce a metal oxide is an oxidation reaction.

Oxidation reactions involve the gain of oxygen.

An example of an oxidation reaction is sodium, that's a metal, reacting with oxygen to produce a metal oxide.

And in this case, the metal oxide will be sodium oxide.

Here we can see a balanced symbol equation for this reaction.

We have 4Na reacting with one molecule of O2, and this will produce two molecules of sodium oxide, which has the molecular formula Na2O.

The sodium has been oxidised because it has gained oxygen.

It's gone from Na to Na2O.

You can see that the sodium has gained oxygen, and therefore it has been oxidised.

This is an example of an oxidation reaction.

What has been oxidised in this reaction? We have a balanced symbol equation for this reaction.

We have four atoms of K reacting with one molecule of O2 to produce a compound with the formula K2O.

So we produce two molecules of K2O.

What has been oxidised in this reaction? The correct answer is A, potassium.

Well done if you chose potassium.

The potassium has gained oxygen to produce potassium oxide, so the potassium has been oxidised.

Magnesium can react with oxygen in an oxidation reaction to produce magnesium oxide.

Magnesium reacts with oxygen and they will produce magnesium oxide.

We can see that shown there in that word equation.

Here, we can see an oxidation reaction where the magnesium, when heated, reacts with oxygen to become magnesium oxide.

Oxygen can be lost from metal oxides in chemical reactions.

Reduction is the loss of oxygen.

And a reaction where both oxidation and reduction takes place is known as a redox reaction.

Let's just recap.

Oxidation is the gain of oxygen.

Reduction is the loss of oxygen.

And a redox reaction is a reaction where we have both oxidation and reduction taking place.

Let's look at an example.

Iron oxide reacts with carbon to produce iron and carbon oxide.

And we can see a balanced symbol equation for the reaction underneath.

The carbon has been oxidised.

It has gained oxygen and produced carbon dioxide.

The iron oxide has been reduced.

It has lost oxygen to produce iron.

This is an example of a redox reaction because we have both reduction and oxidation taking place.

Which of the following statements are true? A, oxidation is the loss of oxygen.

B, oxidation is the gain of oxygen.

C, reduction is the loss of oxygen.

And D, reduction is the gain of oxygen.

Choose any statements that you think are true.

The correct answers are B and C.

Oxidation is the gain of oxygen and reduction is the loss of oxygen.

Hopefully you chose both of those statements.

Time for our first practise task of today's lesson.

You've got two questions to have a go at answering here.

Question one, write word equations for the following reactions.

We've got statements there in A, B, and C, and we need to turn those into word equations.

So make sure you identify the reactants, then draw an arrow, and then show what the product or products will be.

You've got, A, copper reacts with oxygen forming copper oxide, B, solid lead burns in oxygen when heated to form an oxide, and C, lithium reacting with oxygen.

For question two, you need to state the substance that has been oxidised and the substance that has been reduced in those reactions.

Look carefully at the reactions shown in question two, A, B, and C, and try and identify what has been oxidised, that means it's gained oxygen, and what's been reduced.

That means what is the substance that has lost oxygen.

Pause the video now and have a go at question one and two.

And I'll see you in a moment when you're ready to go over the answers.

Let's see how you got on.

Question one, we needed to write word equations for the following reactions.

A, copper reacts with oxygen forming copper oxide.

Your word equation should look like that.

For B, we should have a word equation showing lead and oxygen as our reactants, and these are going to react to produce the product lead oxide.

And in C, we should have lithium and oxygen as the reactants and these react to produce the product lithium oxide.

Hopefully you were able to identify the reactants and the products and turn these statements into word equations.

Question two, for the following reactions, state the substance that has been oxidised and the substance that has been reduced.

In two, A, aluminium has been oxidised.

It gained oxygen to produce aluminium oxide.

And the chromium oxide has been reduced.

It lost oxygen to produce chromium.

Check carefully that you got those ones correct.

In B, the potassium has been oxidised that gained oxygen to produce potassium oxide, and the iron oxide has been reduced because that lost oxygen to produce iron.

And finally for C, carbon has been oxidised and the zinc oxide has been reduced.

Well done if you've got those questions correct.

We have had a look at how metals react with oxygen in oxidation reactions to produce metal oxides.

Now, we are going to move on to have a look at the extraction of metals.

The reactivity series of metals shows the metals in order of reactivity.

More reactive metals are at the top and the less reactive metals are at the bottom.

If we look at the reactivity series that we have there on the left hand side, we can see that potassium is the most reactive metal at the top and gold is our least reactive metal at the bottom.

The metals are shown in order of decreasing reactivity down the reactivity series.

Carbon and hydrogen are non-metals that are often included for reference in the reactivity series.

We can see where carbon and hydrogen are positioned in the reactivity series there.

Which two non-metals are often included in the reactivity series of metals? Is it, A, carbon, B, oxygen, C, hydrogen, or D, nitrogen? The correct answers are carbon and hydrogen.

These are two non-metals that are often included in the reactivity series of metals.

Well done if you identified carbon and hydrogen.

The reactivity series is really useful when we are trying to determine the method of extraction of a metal.

Unreactive metals which are found at the bottom of our reactivity series such as gold and silver, they are found on Earth as the pure uncombined element.

This means we will find gold atoms not chemically bonded to other atoms, but just as the pure uncombined element itself.

Time for a check for understanding.

Why is gold found in Earth as the element itself? Is it because, A, it has reacted to form gold oxide, B, it is an unreactive metal, or C, gold has a high melting point? The reason that gold is found in Earth as the element itself is because gold is an unreactive metal, so well done if you identified B as the correct answer.

Most metals are found combined with other elements in compounds.

For example, aluminium is found as aluminium oxide.

These metal compounds are found in rocks called ores.

Here we have an image of a copper ore.

So this will contain copper compounds, and this copper ore is called malachite.

Here is a picture of an iron ore, so this is a rock that will contain iron compounds.

And this iron ore is known as hematite.

Here we have a picture of tin ore, and this is a rock that will contain tin compounds.

Most metals need to be extracted from ores found in Earth's crust.

Remember that those unreactive metals at the bottom of the reactivity series we often find as the pure uncombined element.

However, more reactive metals will have reacted and formed metal compounds, so we need to extract the metals from these metal compounds that are found in ores.

Metals that are less reactive than carbon can be extracted from their ores by heating them with carbon.

And we can see where carbon is placed on a reactivity series and the metals that are less reactive than carbon.

Time for a check for understanding.

Use the reactivity series to work out how iron can be extracted from its ore.

Look at the reactivity series and see where iron is positioned.

How can we extract iron from its ore? Do we need to, A, heat with carbon, B, heat with copper, or C, heat with hydrogen? The correct answer is, A, heat with carbon.

If we look on the reactivity series, we can see that iron is less reactive than carbon, and therefore we extract it from its ore by reacting it with carbon.

Metals that are more reactive than carbon, such as potassium and aluminium, are extracted from their ores using electrolysis.

Here we can see on the reactivity series the position of carbon and we can see those metals that are more reactive than carbon.

We've got potassium, sodium, calcium, magnesium, and aluminium.

Electrolysis is used to extract these metals from their ores.

And electrolysis is a process that uses electricity to break down a compound.

Electrolysis involves passing a current through a molten or aqueous ionic compound so that the ions discharge, so they lose their charge, and the compound is separated.

The image shows the apparatus that we may use to perform electrolysis in the lab.

We have a power supply and then we have wires with crocodile clips holding the two electrodes.

We have the anode and the cathode.

And then we have our molten or aqueous ionic compound.

A disadvantage of electrolysis is that it requires a lot of energy.

We need energy to melt the compound into the molten form.

And we also need energy to produce an electrical current.

Therefore, we only use electrolysis to extract metals from their ores if they are more reactive than carbon.

If they are less reactive than carbon, then we will extract those metals from their ores by reacting them with carbon.

Time for a question.

What process is used to extract aluminium from aluminium oxide? Have a look at the reactivity series so you can see the position of aluminium on the reactivity series.

Will we extract aluminium by, A, using displacement, B, reduction by carbon, or C, electrolysis? The correct answer is C, electrolysis.

Aluminium is more reactive than carbon, therefore we cannot heat the aluminium with carbon.

Instead, we need to use electrolysis to extract aluminium from aluminium oxide.

Time for another practise task.

In this practise task, you've got three questions to have a go at.

Question one.

Why does gold not need to be extracted from an ore? Question two.

Use the reactivity series to determine how each of the following metals can be extracted from their ores.

So we've got iron, gold, magnesium, zinc, calcium, and copper.

And finally, question three, why do scientists not use electrolysis to extract zinc from its ore? Pause the video now.

Have a go at these questions and then come back when you're ready to go over the answers.

Let's see how you got on.

Question one.

Why does gold not need to be extracted from an ore? That's because gold is an unreactive metal and it is found in Earth as an uncombined element.

Question two.

How can each of the following metals be extracted from their ore? Iron is less reactive than carbon, and therefore we can extract it by heating with carbon.

Gold, that was a bit of a trick question there because gold does not need any chemical extraction process because gold is found as a pure uncombined element.

Magnesium, we would use electrolysis to extract magnesium from its ore because it is more reactive than carbon.

Zinc is less reactive than carbon.

We could heat zinc compounds with carbon.

E, calcium is more reactive than carbon, so we would need to use electrolysis.

And F, copper, we could heat again with carbon because copper is less reactive than carbon.

Question three, why do scientists not use electrolysis to extract zinc from its ore? That's because zinc is less reactive than carbon.

It can be extracted from its ore by heating it with carbon.

We do not want to use electrolysis if we don't need to because electrolysis requires energy.

It requires energy to melt the zinc compound, to make it molten and also to produce an electrical current.

You may not have used the exact same wording there in your answer, but hopefully you included lots of the key points in your answer.

We have looked at metal oxides and extraction of metals.

Now, we are going to move on to the final part of our lesson, reduction by carbon.

We mentioned earlier that most metals exist as metal compounds in ores.

And those metal compounds are often metal oxides.

If the metal is less reactive than carbon, then it can be extracted by heating the metal oxide with carbon.

Here, we've got an example.

We have zinc oxide and we are going to heat that with carbon.

And because the carbon is more reactive, it will displace the zinc in the zinc oxide and we will produce zinc plus carbon dioxide.

And we can see a balanced symbol equation for that reaction too.

The zinc oxide has been heated with carbon and the zinc you'll notice has been extracted from the zinc oxide ore.

So in our products we now have the zinc that we wanted and we've managed to extract it from that zinc oxide.

Iron is extracted from iron ore in a blast furnace.

The iron oxide reacts with carbon.

The carbon is more reactive than the iron, so it will displace the iron in the compound and we produce iron and carbon dioxide.

Here, we can see the product is iron.

We have managed to extract the iron from the iron oxide.

This process is expensive as high temperatures are needed.

We can see an image there showing molten iron from a blast furnace.

When we extract metals by heating them with carbon, the carbon gains oxygen to produce carbon dioxide.

And we can see the reaction there again of iron oxide reacting with carbon to produce iron and carbon dioxide.

The carbon has been oxidised because it has gained oxygen.

Now, where did that oxygen come from? That oxygen came from the iron oxide.

The carbon caused that iron oxide to lose oxygen, so we can describe the carbon as a reducing agent.

It caused the iron oxide to be reduced.

So the thing that is oxidised is also known as a reducing agent as it causes something else to be reduced.

The iron oxide has lost oxygen.

It has gone from iron oxide to iron.

When something loses oxygen, we describe it as being reduced.

So the iron oxide has lost oxygen and it has been reduced by carbon because the iron oxide has lost oxygen and caused something else to gain oxygen.

We can describe the iron oxide as an oxidising agent, and it caused the carbon to be oxidised.

The substance that is reduced is known as an oxidising agent.

And just to recap, the substance that is oxidised is also known as a reducing agent.

Let's see if we can use what we've just learned to answer this question.

Identify the reducing agent in the following reaction.

Remember, the reducing agent is the substance that has been oxidised itself.

And as it's oxidised, it causes something else to be reduced, so it's known as a reducing agent.

Look at that reaction between zinc oxide and carbon and they react together to produce zinc and carbon dioxide and see if you can identify the reducing agent.

Is it, A, zinc oxide, B, carbon, C, zinc, or D, carbon dioxide? The correct answer is carbon.

Carbon has been oxidised to carbon dioxide.

And in doing so, it has caused the zinc oxide to be reduced to zinc, so the carbon is the reducing agent.

Time for our final practise task of today's lesson.

For this task, you've got two questions.

First of all, the manufacturer of lead involves the reduction of lead oxide with carbon.

Carbon dioxide is one of the products in this reaction.

First of all, you need to write a word equation for this reaction.

Then you need to identify which substance has been oxidised and which substance has been reduced.

And finally, what is the reducing agent and the oxidising agent in this reaction? Once you've done that, question two is to explain how oxygen can be removed from iron oxide to produce iron.

Pause the video now.

Have a go at answering these questions and then we'll go over the answers when you come back.

Question one, A, we needed to write a word equation for this reaction.

We had lead oxide and that was reacting with carbon, and they produced lead and carbon dioxide.

Well done if you got that question correct.

In B, we have to identify which substance has been oxidised and what's been reduced.

The carbon has been oxidised because that gained oxygen to produce carbon dioxide and the lead oxide has been reduced because that lost oxygen.

The reducing agent is therefore the carbon.

The carbon has been oxidised in the process.

It caused the lead oxide to be reduced, so the carbon is the reducing agent and the lead oxide is the oxidising agent.

A difficult question there at the bottom, so well done if you got that correct.

Question two, explain how oxygen can be removed from iron oxide to produce iron.

So, your answer may include that you would need to react the iron oxide with a more reactive element such as carbon, and the iron oxide will be reduced by that carbon to produce iron.

An alternative answer that you may have written is to perform electrolysis using molten iron oxide.

However, electrolysis uses lots of energy, and therefore we normally only use it to extract metals from their ores if they are more reactive than carbon.

Hopefully you got that question correct.

Well done if you did.

We've reached the end of today's lesson on extraction of metals by reduction.

Let's just summarise some of the key points that we've covered in today's lesson.

Unreactive metals are often found in the Earth as pure metal.

Metals that are less reactive than carbon can be extracted by heating their oxides with carbon.

A metal oxide is said to be reduced by carbon because the metal oxide loses oxygen.

Carbon is oxidised when it reacts with a metal oxide because it gains oxygen to form carbon dioxide.

Well done for all your hard work throughout today's lesson.

I've really enjoyed the lesson and I hope you have too and that you're able to join me for another lesson soon.