Lesson video

Hello, my name is Mrs. Collins, and I'm gonna be taking you through your learning today.

This lesson forms part of the materials unit and is called "the reactivity series for metals".

By the end of this lesson, you'll be able to use experimental evidence to organise several metals in order of reactivity.

Here are the key words for today's lesson.

Reactivity series, effervescence, and exothermic.

Some of those words will be familiar to you, but others will be new.

What I suggest you do is pause the video at this stage, read through the definitions, and write down any notes that you feel are important.

Today's lesson has been divided into two separate sections.

So first of all, we're gonna look at the reaction of metals, and then we're gonna look at the reactivity series of metals.

So let's get started on part one.

Metals can react with dilute acid to form salts and hydrogen gas, and we can show this in a general equation.

Metal plus acid forms salt and hydrogen.

Let's have a look at an example.

So this is magnesium reacting with an acid.

Now you can see there's effervescence forming there, and if you were to touch that, you'd feel it was warm because it's exothermic.

And effervescence is a scientific term used for bubbles of gas when bubbles of gas are formed.

So effervescence.

And exothermic means that it's feeling hot to the touch.

So energy is being released from the reaction.

We can collect the gas that's being produced during the reaction and test it to prove that it's hydrogen.

First of all, we place a test tube over the top of the reaction to collect the gas, and then test it using a lighted splint.

Here there will be a squeaky pop to show that hydrogen's being produced.

In a moment, we're going to show that reaction taking place so that you can hear the pop.

But before we do that, we're gonna look at the equation for the reaction.

So in this case, we've got magnesium reacting with hydrochloric acid to form magnesium chloride and hydrogen.

Magnesium chloride is the name of the salt produced in this reaction.

It's a magnesium because magnesium was the metal involved in the reaction, and it's chloride because the metal was reacting with hydrochloric acid.

Let's watch the video.

Now we're gonna look at the reaction between zinc and sulfuric acid.

Now we can see some effervescence, but notice there's less than when magnesium reacted with an acid, and that's important to note at this stage.

If we were to touch the test tube, it would feel warm.

This shows us the reaction is exothermic, and we can prove this by putting a thermometer inside the reaction, and finding the temperature at the start, and then the highest temperature during the reaction.

And this will give us the temperature change.

Zinc reacts with sulfuric acid to form a salt called zinc sulphate, and hydrogen gas.

And we can represent this in an equation.

So zinc plus sulfuric acid forms zinc sulphate plus hydrogen.

So metal plus acid forms a salt plus hydrogen.

Notice the name of the salt in this equation.

So again, the zinc has come from the metal in the reaction, and the sulphate has come from the sulfuric acid.

We can also represent this equation using symbols.

Here's a question based on what we've learned so far.

When calcium is added to a dilute acid, effervescence is observed.

Is that true or false? And then look at the information below to use it to justify your answer.

Pause the video now and have a go at the question, and I'll see you when you're finished.

Welcome back.

So hopefully you've realised that this is true, and this is true because hydrogen gas is produced when some metals are added to acid.

Calcium is a metal, and it's been added to dilute acid to form effervescence, which is the hydrogen gas being produced.

So well done if you've got that correct.

Let's consider the reaction between metals and water now.

So some metals react with water to produce a metal hydroxide and hydrogen gas.

So we've got general equation for the reaction again.

So metal plus water forms metal hydroxide plus hydrogen.

So here's an example.

This is lithium, and it's been added to a trough of water containing universal indicator.

Now you can just see it whizzing across the surface there of the water.

The water appears green because the pH of water is seven, which is neutral.

And then underneath the metal, you can see that the colour is changing.

So the universal indicator colour is changing, and it's actually going purple.

So the lithium is moving across the surface of the water.

That'd be one of our observations.

And the second observation is that fizzing is being heard.

So there's definitely effervescence, and that shows us that a gas is forming, and the universal indicator is changing from green to blue, and that tells us that it's alkaline.

So looking at the reaction again, lithium reacting with water, with the universal indicator in place, we can interpret those observations that we've made earlier.

So we know that lithium metal reacts with water.

We can see that happening.

We know that a gas has been produced, and if we were to collect that gas and test it, it would burn with a squeaky pop.

So that tells us that the gas is hydrogen, and the blue universal indicator shows us that an alkali is present.

So that alkali is lithium hydroxide.

And that can give us the equation for the reaction.

So lithium plus water forms lithium hydroxide plus hydrogen, and there we've got a balanced chemical equation underneath.

This time, we're gonna add potassium to a trough of water, and we're going to see what happens.

There's the potassium reacting with the water.

Notice the difference.

So the potassium is moving quickly across the surface of the water, much faster than the lithium.

And you can see there, there's a lilac flame.

This shows the reaction is exothermic, because it's released energy to the surroundings.

And we also have effervescence as well.

So the equation for this reaction is very similar to the lithium.

So we've got potassium plus water, this time forming potassium hydroxide plus hydrogen, and we can see the equation there.

So here's a question based upon the learning so far.

When sodium reacts with water, effervescence is observed, and universal indicator changes from green to blue.

What is produced? Have a go answering that question, pause the video now, and I'll see you when you've finished.

So hopefully you've worked out that sodium hydroxide has been produced during the reaction.

The universal indicator has changed from green to blue.

So that shows an alkali has been produced, and the alkali is sodium hydroxide.

And then hydrogen gas has been produced.

We know when a metal reacts with water, it produces hydrogen gas, and the observation shows that effervescence is happening.

So we know that a gas is being produced.

So well done if you got that right.

Let's have a look now at the reaction between metal and oxygen.

So when a metal reacts with oxygen, it forms a metal oxide, and there's the general word equation for this reaction.

So metal plus oxygen forms a metal oxide.

So if we consider magnesium reacting with oxygen, this would be the equation for the reaction.

Magnesium plus oxygen forms magnesium oxide.

So you can see there we've got metal plus oxygen forming a metal oxide.

When magnesium is heated, it reacts with oxygen in the air.

The reaction is exothermic.

During the reaction, a bright white light is observed, and at the end of the reaction, a white solid is produced.

This solid is magnesium oxide.

So different metals react with oxygen at different rates.

Some are very quick, like magnesium, and some are really slow.

So this is an example of silver reacting with oxygen in the air and changing colour.

So it appears to go dull, but that is actually silver oxide forming on the surface of the goblet.

So if we clean it, what we're doing is we're taking the silver oxide layer off the surface of the silver, returning it back to silver again, but that surface can react with oxygen in the air and become dull again.

And this is why, if you do have any silver, you have to keep cleaning it over time.

Here's a question based on what we've learned so far.

So we're gonna complete the equation between zinc and oxygen.

So try and think back to what the general equation for the reaction between zinc and oxygen is, and then work out what the product might be.

Have a think about your answer, maybe pause the video if you need to, and then we'll go through it.

So remember, the general equation for the reaction between a metal and oxygen is metal plus oxygen forms a metal oxide.

So the answer is B, zinc plus oxygen forms zinc oxide.

Well done if you got that correct.

We're now gonna have a look at task A, the reactions of metals.

So we've got two questions here with several parts.

So question one asks for the meaning of the words effervescence and exothermic.

And then question two looks at the reaction between sulfuric acid and iron.

Effervescence has been observed during the reaction.

So describe how you would test the gas to show it's hydrogen.

How would you show the reaction was exothermic? And you need to complete the word equation between iron and sulfuric acid.

So pause the video here, and have a go at answering those questions.

Welcome back.

So let's go through the answers to those questions then.

So 1a, effervescence is when bubbles of gas are produced in a liquid, or you could say that the liquid is fizzing, and then exothermic is a type of reaction when a substance transfers energy from the reactants to the surroundings.

And you could give an example if you wanted to.

So in this case, we've said combustion.

Question two, when sulfuric acid is added to iron filings, effervescence is observed.

So how would we test the gas to show it was hydrogen? So we would hold a burning splint to the end of the test tube, and if it's hydrogen, it will burn with a loud, squeaky pop.

And then how would you show the reaction was exothermic? Well, this time we need to measure the temperature.

So place a thermometer in the test tube and see if the temperature increases.

Complete the word equation.

The iron plus sulfuric acid forms iron sulphate plus hydrogen.

So well done if you got that right.

So we're moving on to question three and four now.

So question three says, "These tools are made from iron, which looks grey.

After being left outside, they turn a brown colour.

Suggest a reason why." So this is a suggest question.

You have to use your knowledge and apply it to the situation.

Question four, "Aluminium does not corrode because it reacts with oxygen in the air to form a protective layer.

What is this protective layer?" Now you might need to think about that one carefully.

You do know the answer to it, even though you might not know about aluminium and this surface coating.

Think about what happens when aluminium reacts with oxygen in the air, and think about what's formed in that case.

So pause the video, and have a go answering those two questions.

Welcome back.

So let's have a look at question three, first of all.

So the iron has reacted with oxygen in the air to form rust.

And rust is called iron oxide.

But in order for that to happen, there needs to be moisture in the air as well.

So there needs to be water.

So iron is grey, and rust is a brown colour.

This layer on the surface of the aluminium is aluminium oxide.

Remember, when a metal reacts with oxygen, it forms a metal oxide, and the metal in this case is aluminium.

So the oxide must be metal oxide.

Well done if you've got those correct.

We're now moving on to part two of this lesson, where we're looking at the reactivity of metals.

So different metals react in different ways, and we saw that in the first part of the lesson.

If you compared magnesium and zinc and their reaction with acid, you'll have seen there was a completely different amount of effervescence formed in the two different reactions.

So it's important to realise that metals have different levels of reactivity, and some metals are actually incredibly unreactive.

So sodium is an example of a very reactive or a highly reactive metal, and gold is a very unreactive metal.

If we look at these different reactions taking place like we did earlier, what we can do is create a reactivity series of metals, which is almost like a league table.

So we can put the most reactive metals at the top, and the least reactive metals at the bottom.

And we call this the reactivity series of metals.

The group one alkali metals, lithium, sodium, and potassium, are at the top of the reactivity series, and they're highly reactive.

We're going to watch a video, and then we're gonna answer the following questions.

So what you might want to do at this stage is just pause the video and write down the questions, so that when you watch the video, you can answer them.

So question one, why are the alkali metals stored under oil? Question two, how do we know a chemical reaction has taken place? And question three, what is the order of decreasing reactivity? So let's watch the video.

Before reacting the group one metals with water, we have to remove the oil they're covered in.

The metals are stored in oil to prevent them reacting with water and oxygen in the air.

We can see they are so soft, they can be cut with a knife.

The inside is very shiny, but the outside is dull.

The outside has reacted with either water or oxygen in the air, and caused the metal to tarnish.

Let's see how these metals react with water.

So firstly, lithium.

It's reacting quite vigorously.

You can see it moving across the surface there.

It's producing lithium hydroxide and hydrogen gas.

The next metal you see dropped in is going to be sodium.

And this time it's reacting so vigorously and it's so exothermic that the hydrogen gas is igniting with an orange flame, and this time sodium hydroxide's produced.

Lastly, we're going to add potassium to the water.

So potassium reacts much more vigorously and it burns with a lilac flame this time, and potassium hydroxide is produced.

It is possible for us to light the hydrogen gas being released when lithium reacts with water.

If we place a lighted splint next to the gas, we'll see a crimson flame.

Here we've added universal indicator to the water, and it shows that group one metals react with water to form alkaline solutions.

Okay, let's have a look through these questions then.

So why are the alkali metals stored under oil? That's to stop them reacting with oxygen and water in the air.

Remember, these are incredibly reactive metals, and they will react with oxygen in the air.

How do we know a chemical reaction has taken place? Well, there's several bits of evidence.

So we can see effervescence taking place.

We saw the metals move across the surface of the water, and that showed a trail of bubbles.

We saw the universal indicator change from green to blue, and we saw sodium and potassium burst into flames.

So all of that is evidence that there's a chemical reaction taking place.

And then the order of decreasing reactivity.

So you need to put the most reactive metal first, and then have it decreasing in reactivity.

So that's potassium, sodium, and lithium.

So well done if you've got all those answers correct.

So here is the reactivity series for metals.

And you can see there's a number of metals there that we've already come across.

So potassium and sodium at the top there.

We've talked about zinc, we've talked about magnesium, aluminium, and gold.

So at the very top, we've got the very reactive metals, and at the bottom, the very unreactive metals.

Now what's interesting is we can put two non-metals into this series as well.

And later on in your learning, you will understand precisely why this is the case.

But at this stage, we're just going to touch on them.

So we've got carbon at the top there, and we've got hydrogen towards the bottom there.

And they're important, because they can help us understand some of the reactions of metals.

Now the reactivity series can be used to predict how different metals are going to react, and we're gonna have a look at the summary here.

So first of all, the higher the position of the metal in the reactivity series, the more vigorous it's going to react.

So potassium will react more vigorously than calcium, because it's higher in the reactivity series.

If we look at the reactions with oxygen, we can see that gold and below is very unreactive with oxygen, but silver and above does react with oxygen.

So we saw that silver will tarnish over time as it reacts with oxygen in the air, but we also know that metals like potassium and sodium will react very vigorously with oxygen.

In terms of reacting with dilute acids, now this is important.

This is why hydrogen is in the table.

So anything above hydrogen in the table will react with a dilute acid.

Anything below hydrogen will not.

Then we got the reactions with water, and you can see only the most reactive metals at the very top of the table will react with water.

And that's important to remember later on.

You might want to pause the video here and just digest that a little bit more, and maybe make a couple of notes.

So we can use the reactivity series to make predictions about how metals will react in certain situations.

So sodium is near the very top of the table, so it will react with water with a vigorous reaction, and we can write a word equation for this.

So sodium plus water forms sodium hydroxide plus hydrogen.

Remember, metal plus water forms metal hydroxide plus hydrogen.

Silver is below hydrogen in the reactivity series, so it will not react with dilute acids.

We could write a word equation like this.

Silver plus hydrochloric acid has no reaction.

And remember, that's because silver is below hydrogen in the reactivity series.

And what I'd like you to do is read through this question and answer it using the reactivity series to help you.

So which statements about the reactivity series for metals are correct? So pause the video, read through the statements, and decide which ones are true and which ones are false, and put a tick next to the ones that are true.

Welcome back.

So let's see which statements are correct.

So the reactivity of metals does increase as you go up the series.

Remember, potassium is more reactive than sodium.

And the second one that's correct is calcium will react with water.

So that's important to remember.

So well done if you got that correct.

The reactivity series of metals can be used to determine the method by which they're extracted from the ground.

Anything that's more reactive than carbon needs electricity to help them be extracted.

So this is extraction by electrolysis, a process called electrolysis, and you will learn about electrolysis later in your lessons.

Those lower than carbon can be extracted by displacement with carbon.

And again, we're going to be talking about displacement reactions later in the topic.

But those that are at the very bottom of the reactivity series, those that are credibly unreactive, can actually be extracted as themselves.

So gold, we find as gold in the ground.

It's not combined with other chemicals normally, so that makes it easier to extract.

Here's a question based on that learning that we've just covered, and it's a true or false question.

So you need to decide if the statement is true or false, and then you need to justify it using the statements underneath.

So pure gold is found in nature.

So by pure gold they mean not combined with any other substance.

So decide if that statement is true or false, and then justify it.

Pause the video here, answer the question, and I'll see you when you're finished.

So hopefully you've realised that that statement is true.

So gold is not found combined with other substances.

It's found as pure gold.

And the reason is because it's found at the bottom of the reactivity series.

So well done if you got that correct.

We're now gonna move on to task B, and this is going to be challenging in places, but you do have the information you need to answer the question, so do think carefully about your answers, and I'm going to support you through those answers.

So firstly, we've got a whole series of metals here that are reacting with dilute hydrochloric acid, and you need to look at the results.

So have a look at the bubbles that are being produced, the effervescence that's being produced in each of those beakers.

So A, you need to name the gas that's produced during the reaction.

So reaction between metals and acids.

List the metals in increasing order of reactivity, so the least reactive first.

And then give a reason for your answer.

And then you need to think, do you think one of those is copper? Give a reason for your answer.

So consider your answer to that question, pause the video, and I'll see you when you're finished.

Welcome back.

So let's go through the answers to that question then.

Firstly, we need to name the gas that's produced during the reaction, and that's hydrogen gas.

And remember, we can test that gas to prove it's hydrogen.

It will have a squeaky pop.

Then we need to list the metals in increasing order of reactivity, and give a reason.

So the least reactive is A, then it's D, C, and B.

And the number of bubbles produced is related to the reactivity.

So the more bubbles are produced, the more reactive the substance.

So the least reactive substance is metal A, and the most reactive substance is metal B, and we can tell because of the effervescence.

And the last question was slightly more difficult, and you really needed to think about it.

So the answer is no, because copper does not react with dilute acids, because it's lower than hydrogen in the reactivity series, so it doesn't react.

So metal A, even though it might look like copper, isn't actually copper.

So well done if you got the answers to that question correct.

Now we're gonna move on to question two.

And this time you've got the reactivity series there to refer to.

So it says, "Complete the word equations or write 'no reaction' next to them." So for each of those reactions, think about what the products might be.

So metal plus water forms what? Metal plus oxygen forms what? Metal plus acid forms what? And look at where those metals are in the reactivity series.

Remember, for some of them, you need to look at how they relate to hydrogen, the position of hydrogen in the reactivity series.

So pause the video here, and have a go at answering the question.

Welcome back.

So let's go through each of those equations.

So A, lead plus water.

Now there's no reaction there, because only the most reactive metals will react with water.

So remember that.

Next one, sodium and water.

Well, this time there is going to be a reaction, because sodium is right near the top of the reactivity series.

So sodium plus water form sodium hydroxide plus hydrogen.

Next one, silver and oxygen.

Silver does react with the oxygen, and it forms silver oxide.

We've then got gold and nitric acid.

Now gold is below hydrogen on the reactivity series, so it's not going to react with the acid.

It won't produce anything, it won't react with it.

And then calcium and hydrochloric acid.

Well, calcium is above hydrogen in the list, so therefore it will react, and it will form calcium hydroxide plus hydrogen.

Now well done if you got that correct.

That was a little bit more challenging, but I'm sure you did well.

Question three.

This time we've got a vigorous exothermic reaction taking place, when the potassium reacts with water, and the hydrogen gas ignites and a lilac flame is observed.

So we need to think about what evidence is there for an exothermic reaction.

So how do we know it's an exothermic reaction? If the calcium was added to water, how would the reaction compare? Okay? So comparing potassium to calcium.

And look at the reactivity series to help you answer that question.

And then lastly, predict what you'd see if zinc was added to water.

And look at where zinc is on the reactivity series to make that prediction.

So pause the video now, and have a go at answering that question.

Welcome back.

So let's go through the answers.

So what is the evidence for an exothermic reaction? So good thing to do is to define what the word means, first of all, and then answer the question.

So exothermic means that energy is transferred from the substance to the surroundings, the hydrogen gas ignites, and a lilac flame is observed.

So that's the evidence that that's happened.

If calcium was added to water, how would the reaction compare and why? Well, calcium is less reactive than potassium.

So think about how that might affect the results.

So as calcium is quite high in the reactivity series, it would still, I would still expect to see a vigorous reaction with lots of effervescence, but the reaction would not get hot enough to burst into flames.

And then predict what you'd see if zinc was added to water.

No reaction.

'Cause zinc is lower down the reactivity series.

So remember, only the most reactive metals will react with water.

Well done.

Here's a summary for today's lesson.

Some metals react with acid to produce a metal salt and hydrogen gas.

Some metals react with water to produce a metal hydroxide and hydrogen gas.

Some metals react with oxygen to form a metal oxide.

The reactivity series of metals shows how vigorously metals react compared to each other.

And the higher the position of the metal in the reactivity series, the more vigorous it's likely to react.

So thank you very much for joining me today for this lesson.

I hope you learnt a lot.