Lesson video

Hello, my name is Mrs. Collins and I'm going to be guiding you through the learning today.

This lesson forms part of the unit "Materials" and is called "Catalysts." So let's get started.

So during this lesson, we're going to describe how catalysts, including enzymes, speed up chemical reactions.

Here are the keywords for this lesson.

Catalyst, enzyme, and chemical reaction.

Now some of these words you will have come across before, but others will be new to you.

So pause the video here, read through the descriptions, and make any notes you feel will be useful.

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

So firstly, we're going to talk about catalysts generally and how they're used in industry.

And then we're going to talk about enzymes, which are biological catalysts.

They're found inside living things.

So let's start with part one then, catalysts.

A good place to start is a definition.

So a catalyst is a chemical that speeds up the rate of a chemical reaction without being used up during the reaction.

And that's important because it means that we can use that chemical again to speed up another chemical reaction.

Now during this first part of the lesson, we're going to talk about the chemical hydrogen peroxide.

Now hydrogen peroxide, as you can see, is a colourless liquid, and it breaks down or decomposes over time into water and oxygen.

But this is actually quite a slow process.

We might see oxygen bubbles forming slowly over time inside that liquid.

Chemical decomposition is a type of chemical reaction.

Now hopefully you remember that chemical reactions happen when atoms are rearranged to make new products.

And we can observe these changes by looking out for things like bubbles or effervescence and sometimes colour changes and sometimes we can see the new product being formed.

The symbol equation for a reaction shows how these atoms rearrange, and we can see the equation based on the breakdown of hydrogen peroxide here.

So if you notice, hydrogen peroxide is the only reactant, and that's because it decomposes to form the water and the oxygen.

And we can show that in a symbol equation.

And we've coloured the different letters here so that you can see what's happening.

So inside the hydrogen peroxide, we've got hydrogen atoms and oxygen atoms, and you can see they've been rearranged to form the products.

So all of the hydrogen atoms have ended up in the water, but the oxygen atoms have been divided between the water and the oxygen.

In the next slide, we're going to see what happens when a catalyst is added to hydrogen peroxide.

Now as you can see here, we've got a lot of effervescence or bubbling taking place, and the reaction happens quite vigorously.

So when a catalyst is added to the hydrogen peroxide, it speeds up that decomposition reaction.

And the catalyst we're using today is manganese dioxide.

It's a black solid, and when it's added to the flask, we can see there's vigorous effervescence.

And at the end of the reaction, just as we pan down here, you'll see the black manganese dioxide remains in the flask at the end of the reaction.

And that means we can use it again to speed up another reaction, making it quite useful.

We're now going to have a go at a question based on our learning so far.

So which of the following statements best describes a catalyst? Pause the video here, read through the statements, and decide which one you think is correct.

Hopefully you identified that it's a chemical that speeds up the rate of reaction without being used up.

And that's really important, that end bit.

It's not used up during the chemical reaction.

Well done if you got that correct.

So catalysts are specific to particular reactions, and this means different reactions need different catalysts.

And we're going to see an experiment here where we've investigated this.

So different catalysts were added to the same volume of hydrogen peroxide.

And the catalysts that we're going to use are iron oxide, copper oxide, and manganese dioxide.

So they're all catalysts.

And a drop of washing-up liquid was added to the hydrogen peroxide to help show which one produced the most gas.

So it'll help form foam in the reaction.

You'll be able to see that happening.

So now we're going to watch the video to see what happened during the experiment.

Remember, each of these measuring cylinders contains hydrogen peroxide and a drop of washing-up liquid.

We're going to add a spatula full of each of the three catalysts and observe what happens during the reaction.

As we can see, we're shaking each of them just to enable the reaction to start.

Let's watch the results.

As we can see, one of the reactions is producing a large amount of foam, and this is the catalyst catalysing the reaction so that lots of oxygen is being produced and that's causing foam in the washing-up liquid.

In the second one, we can see a small amount of foam being produced, and in the first one, very little.

Here are the results of that experiment that we just watched.

Manganese dioxide is definitely the most effective catalyst.

It produced a lot of foam during that experiment, and that's because lots of oxygen was produced and it was produced very quickly.

You can see a little bit of foam on the top of the copper oxide and not very much at all on top of the iron oxide.

So it shows you how much oxygen were produced in those reactions.

So iron oxide and copper oxide would not be good choices for catalysts for this particular reaction because they didn't really speed it up.

And that confirms that catalysts are specific to particular reactions.

Now we're going to have a go at another question.

This time, it's true or false.

So metal oxides are used as catalysts for all chemical reactions.

So decide if that's true or false, and then underneath, justify your answer.

So pause the video here, answer the question, and I'll see you in a moment.

Welcome back.

So this statement is actually false and this is because catalysts are specific to particular reactions.

Well done if you got that correct.

So catalysts have quite important applications in everyday life, and one example is in a car.

So if you have a petrol or a diesel engine in a car, it produces toxic and polluting gases into the atmosphere.

And we can fit a catalyst into the exhaust system to help reduce these polluting gases.

So the toxic and polluting gases produced in an engine include carbon monoxide, which is a toxic gas, and carbon particulate, so that's little bits of soot, because of incomplete combustion.

We also get nitrogen oxides produced because of the high temperatures.

This causes the nitrogen to react with oxygen in the air.

Now a catalyst fitted to the exhaust system is called a catalytic converter.

And you might have heard of this before.

So cars, petrol and diesel cars, have catalytic converters inside the exhaust system.

And normally, these are made with transition metals like platinum or rhodium, and platinum and rhodium act as catalysts.

And there's an example there.

You can see the catalytic converter inside the exhaust system.

So when it's fitted, chemical reactions inside the converter speed up and less harmful gases are produced.

Now we need to talk about those gases that are produced.

They're less harmful than the nitrous oxides and the carbon monoxide.

So in the exhaust system, the following chemical reactions take place.

So in the first one, the carbon monoxide, which is a toxic gas, reacts with oxygen to form carbon dioxide.

And you can see that uses a catalyst, which is the platinum.

That's what Pt stands for.

Can you see that the catalyst is written on top of the arrow? And that's because it's not used up during the chemical reaction.

So we always put the enzyme or the catalyst above the arrow to show that it's not used up during the reaction.

The other reaction is also catalysed by platinum, and this is nitrogen oxide reacts with carbon monoxide to form nitrogen and carbon dioxide.

Now we know that carbon dioxide is a greenhouse gas, but that is less harmful than the carbon monoxide and the nitrous oxides or the nitrogen oxide.

Catalysts are used in industry to ensure the product is made efficiently and is cost effective.

So here we've got some ammonia-based fertiliser, and many fertilisers are made from ammonia-based chemicals.

Ammonia is produced from nitrogen and hydrogen in the Haber process, and this uses iron as a catalyst to speed up the chemical reaction.

So here's the chemical reaction that takes place.

Nitrogen and hydrogen react together to form ammonia.

And you can see again we've written the iron catalyst above the arrow.

Now you may notice that the arrow is slightly different this time, and this means it's a reversible reaction.

So the reaction can actually go in both directions and that's why you have a bit of an arrowhead going in one direction and in the other.

But as you can see, the iron is increasing the rate of the reaction and it actually increases the rate in both directions.

So it makes both directions faster.

So here we have a question based on the learning so far.

Catalysts have many applications because.

So what I'd like you to do is read through those statements, decide which ones are correct and which ones are not correct.

Pause the video and I'll see you when you're finished.

Welcome back.

So hopefully you've realised that there is more than one correct answer to this question.

So catalysts have many applications because they make chemical processes more efficient by speeding up the chemical reaction.

They make the chemical processes more cost effective.

And they can be reused.

C is incorrect because, remember, catalysts are specific to a reaction.

Well done if you got that correct.

Let's have a go at Task A and we've got several questions here.

So question one is asking you to write a definition for a chemical reaction and for a catalyst.

Question two has an experiment.

So a class carried out an investigation to find a suitable catalyst for a chemical reaction, and you can see the results there in the diagram.

So question A wants to know which chemical was the best catalyst? B, give a reason for your answer.

And C, why didn't all the chemicals catalyse the reaction? So you can see B there doesn't catalyse the reaction.

Pause the video here and answer the questions.

Welcome back.

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

So a chemical reaction is when atoms are rearranged to make new products and changes can be observed.

And you could give several examples there.

So here we've written bubbles of gas forming.

But you can see colour changes and other things as well.

Temperature differences.

The definition for a catalyst.

So a catalyst is a chemical that speeds up the rate of reaction without itself being used up.

For question two, which chemical was the best catalyst? Well, that was chemical C, and you can see that because there's more effervescence or bubbling inside the beaker.

So more bubbles were produced as seen in the beaker, suggesting that the chemical reaction was occurring faster or at a quicker rate.

And then why didn't all the chemicals catalyse the reaction? A catalyst is specific to a particular reaction.

So different reactions need different catalysts.

So well done if you got those questions correct.

Now looking at question three.

So use the following words to complete the sentences below to explain why petrol and diesel cars have a catalytic converter fitted to their exhaust system.

So read through those words and decide which ones best complete those sentences.

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

So a combustion engine produces toxic gases such as carbon monoxide and nitrogen oxides, which are pollutants.

And a catalytic converter is fitted to the engine or the exhaust system to speed up the chemical reactions and reduce the amount of toxic gases going into the atmosphere.

Well done if you got that correct.

Now it's time to move on to the second part of the lesson where we're looking at enzymes.

So an enzyme is what we call a biological catalyst.

It's biological because it's found in living things, and it's a catalyst because it speeds up chemical reactions.

They're not used up in the chemical reaction, remember.

The same as other catalysts.

And we've got an image here of an enzyme.

So an enzyme is a protein and it has this section called an active site.

So it's got a specific shape and the active site is where the chemical reaction takes place.

Here's a question based on that learning.

So we need to decide if this statement is true or false and then justify our answer using the statements below.

So an enzyme is a biological catalyst.

True or false? And then justify your answer.

So pause the video here, answer the question, and I'll see you afterwards.

So an enzyme is a biological catalyst.

It's a molecule that speeds up a chemical reaction in living cells.

Remember that's the biological part.

So it's found in living things.

Well done for getting that correct.

Now you will have learned about enzymes in your biology lessons, particularly when talking about the digestive system.

So the enzyme amylase is used to speed up the breakdown of large starch molecules into smaller glucose molecules.

So if you look at this diagram, we've got a starch molecule, and that's a whole series of glucose molecules chemically bonded together.

We add the amylase enzyme and that then catalyses the reaction, breaking down the starch into these glucose molecules.

Now this chemical reaction takes place in the active site of the enzyme.

And what we call the starch in this instance is a substrate.

So the substrate is the substance that goes into the active site of the enzyme.

We can see that in a series of diagrams now.

So during the enzyme reaction, the substrate, which in that case was starch, enters the active site of the enzyme, which in the previous example was amylase.

The chemical reaction takes place.

So the starch breaks down.

And this produces the products which leave the active site.

And in the previous case, that would've been glucose.

Now enzymes, like other catalysts, are specific to particular reactions.

So for the reaction to be catalysed, the substrate, that's the molecule or group of molecules, must fit into the active site.

And that's why it's specific.

And we can say this is acting a little bit like a lock and key.

So we use something called the lock and key model.

So in this example, the substrate acts like the key, the lock acts like the enzyme, and the active site is a little bit like the place where the key fits into the lock.

So a lock and key is often used to model an enzyme, and only the correct-shaped key will open the lock.

And you can see how that makes it quite a good model to explain about how enzymes are quite specific to particular chemical reactions.

So only the correct-shaped substrate will fit in the active site.

Only the correct key will unlock the lock.

Here's a question based on that learning.

A lock and key is often used to model an enzyme.

And what does the key represent? So pause the video here, think about your answer, and I'll join you when you're finished.

So in the lock and key model, the key represents the substrate.

Well done if you got that correct.

So catalase is an enzyme that's found in nearly all living things that are exposed to oxygen and it speeds up the decomposition of hydrogen peroxide.

So back to hydrogen peroxide again.

So if you remember, hydrogen peroxide decomposes into water and oxygen.

And here we've got the chemical equation for that as well.

And hydrogen peroxide's got the potential to do harm to living cells, so it needs to be removed.

And this is done by speeding up the decomposition reaction and the catalase enzyme can speed up that reaction.

Now interestingly, potatoes, which are exposed to oxygen, contain catalase, and we can investigate the rate of decomposition at different temperatures and learn more about enzymes.

So what we're going to do is see a chemical reaction taking place here.

And for this reaction, we're going to need this range of equipment.

So we need a potato because we're going to use potato cells and the catalase that's found inside the potato cells.

A cork borer.

So that is used to bore holes inside the potato.

We've got hydrogen peroxide.

And potato samples here that we're going to place inside the hydrogen peroxide.

We've got test tubes for the reaction to take place.

Washing-up liquid, which is going to show the foaming again, as with our previous experiment.

A beaker for hot water, and iced water.

And that's how we're going to change the temperature of this particular experiment.

So now let's watch the video to observe the effect of temperature on the rate of reaction of catalase enzymes from potatoes to learn more about the enzymes and the temperature.

So the purpose of this investigation is to observe the effect of temperature on the rate of reaction.

So first of all, we're going to place one of the potato cores into the iced water and then the other potato core into hot water.

And this will change the temperature of the reaction because the two potatoes will be at different temperatures.

Next, we're going to add five centimetre cubed of hydrogen peroxide and place it into each of three test tubes.

This ensures that the volume of hydrogen peroxide is the same for each individual experiment.

We're then going to take one centimetre cubed of washing-up liquid and place that into each of the three test tubes.

The three temperatures that we're going to test are room temperature.

You can see the potato chip on the tile there next to the washing-up liquid.

The cold temperature and then the hot temperature, and see what happens for each individual experiment.

Now we're going to take each of the pieces of potato and place them into the test tube.

So firstly, here's the one that was placed in the ice water, the one that was at room temperature, and lastly, the one from the hot water.

And we're going to leave them now and see what happens and observe the results.

Here are the results after a few minutes.

So now we've watched that video, what we're actually going to do is have a look at the results themselves.

So here are the results from that experiment.

At which temperature does the catalase work best? So I'll just give you a moment to think about that.

And it's actually at room temperature.

So temperature really affects the way that enzymes work.

So if it's too hot, then that can prevent the reaction from taking place at all.

And if it's too cold, it can slow down the reaction.

Let's have a go at Task B.

So for this part, we're going to define what an enzyme is.

You're going to have a go at labelling the diagram.

You're going to name an enzyme.

See if you can remember the name of one.

And we're going to describe why the lock and key model is a good model.

So pause the video here and then I'll see you when you're finished.

So an enzyme is a biological catalyst that speeds up reactions in living things.

You need to make sure you mention it's a biological catalyst.

In terms of labelling the diagram, we've got the substrate, the active site, and the enzyme.

And then naming enzymes, those are the two that we've mentioned in this lesson.

But you may well remember some other ones from your biology lessons.

So well done if you've included those two.

Now we're going to go through question three.

So the lock and key is often used to model an enzyme.

Describe why it's a good model.

So we need to say what the various parts of the model represent, first of all.

So the lock represents the enzyme.

The keyhole represents the active site.

And the key represents the substrate.

And then, only the correct-shape key will open the lock.

So that's what makes it a good model because it represents what an enzyme does.

And only the correct-shape substrate will fit into the active site.

And the lock can be used many times and so can the enzyme.

And that's really important because remember, catalysts can be used more than once.

So well done if you got that correct.

Now we're going to have a look at question four.

So proteins are digested in the stomach and small intestine.

Protease enzymes break down proteins into amino acids.

Complete the diagram.

Now although we've not talked about protease enzymes in this lesson, what you need to do is apply your knowledge and understanding of what we've covered so far to this particular question.

So pause the video now and answer the question.

Let's take a look at the answer to this question then.

So we've got a section of protein molecule and the question says, an enzyme, the protease enzyme breaks down proteins into amino acids.

So remember, we need to put protease over the arrow because it's not used up during the chemical reaction.

And then we need to show that the products are the amino acids and that they're chemically not bonded to each other.

So well done for getting that correct.

Here is a summary of today's lesson.

So a catalyst speeds up a chemical reaction without being used up or chemically changed during the reaction.

Catalysts are specific to particular reactions, and different reactions require different catalysts.

And enzymes are biological catalysts that speed up the reactions in living cells.

So thank you very much for joining me for today's lesson, and I hope you enjoyed it.