Lesson video

Hi, it's Miss Simkin back again for your next science lesson.

And actually you can't see him, but Charlie is ready for our next science lesson too.

Let's take a look at what our lesson question is for today.

So today, we are going to be learning all about chemical reactions and how to tell whether a chemical reaction has taken place.

Before we begin, can you please check that you've got these things for today's lesson, an exercise book or a piece of paper, a pencil, a colouring pencil, and a ruler.

If you don't have those things, then can you please pause the video and go and grab them for me now please? Great, you're also going to need these star words.

So we're going to practise saying them.

I'm going to say them, then you're going to say them when I point to the screen like this.

Particle.

Physical.

Chemical.

Reactant.

Product.

Great, good job.

And we're going to talk about what those words mean as we do our lesson, although particle we can define already.

So a particle is essentially anything that has mass, and everything in the world is made up of particles.

In today's lesson, this is what we're going to cover.

We're going to start with some recap like we always do.

We're going to look at the difference between physical changes and chemical reactions.

Then we're going to look at word equations.

Then we're going to look at the indicators or the signs of a chemical reaction.

Then we're going to do a quick investigation.

So let's start with our recap.

First thing I want you to do, see if you can remember, and also to get that blood moving to your brain is can you show me in your screen your actions for solid, liquid, and gas? So use your hands as particles, and show me those actions, please.

Great, so let's practise them together.

We've got solid like this, so our particles are touching, and they vibrant.

Do your solid action for me again.

You can make your whole body vibrate.

Great, liquid is like this.

So they're still touching, but they can slide past each other.

Show me your action for liquid.

And last, our gas one.

Moving really fast all around in open space, and they're not touching each other.

They might bump into each other, but they're not touching.

Show me your action for gas.

Go! Fantastic.

Well done.

Okay, next bit of recap, I've got two particle diagrams for you.

So you've got two beakers of water, and you can see the particle diagrams for each.

What's the difference between these two beakers of water? Have a think for me.

Write down your answer if you want.

You might be able to spot more than one.

Great, so the difference is that, one of the differences you might have written is that one of these samples of water, the one on the left, is pure.

There's only one type of particle in it.

But the one on the right is impure.

You can see that there's a mixture of two different types of particle.

So it's impure.

It's got an impurity in it.

You might also recognise these diagrams from our lesson on dissolving.

The one on the right, the water, has something dissolved in it.

It's got a solid particle that's been surrounded by liquid particles.

Well done if you spotted and remembered that.

And your last bit of recap, can you tell me what separation strategy this is? Is it evaporation, filtration, or sieving? Point at your screen and say it really loudly.

It's.

It's sieving, great.

And we looked at lots of separation methods last lesson, and sieving is when you separate a solid from a liquid, so rice in this example from water, but the solid needs to be insoluble, which means it doesn't dissolve.

Well done if you remembered that.

Let's move on to today's lesson.

So in today's lesson, we are going to look at the difference between physical changes and chemical reactions.

And the reason that these two things are different is because of the particles.

Okay, I'll explain that in a moment.

I'm going to start just by showing you a physical change and a chemical reaction.

So I've got here some ice.

And very simply, example of a physical change is ice melting into water.

So if I just hold this in my hand, you can see, my hand's very warm, the ice is starting to melt quite quickly into water, which you can see dripping down from my hand.

Ooh, I've got chilly hands now.

That is an example of a physical change because the ice is changing.

It is changing.

It's a change.

It's changing from ice to water.

And the particles are changing their arrangement.

So they're going from solid particles in ice to liquid particles in water.

So they're changing their arrangement.

But the particles themself are the same.

They're still water particles even when they're solid in ice or liquid.

Okay, so that's an example of a physical change.

Now I'm going to show you an example of a chemical reaction.

What am I going to show you an example of? Say it to your screen.

A chemical reaction, great.

So I've got a piece of paper here.

I'm just going to rip a smaller piece.

I've got a box of matches.

This is a demonstration, I should just say.

I'm going to light a match and burn the paper.

And you should be watching, not doing this along with me.

You should never be using matches at home without permissions from your parents or supervision.

That means when they're watching you.

Okay, so you're just going to watch me do this.

I've got a piece of paper.

I'm going to light my match.

Ooh, I'm going to try to light my match.

Oh, nearly.

Cross your fingers.

Keep your fingers crossed.

Come on, Miss Simkin.

Okay, so I've lit my match, and I've used it to burn this piece of paper, and I'm going to hold it over this dish.

So we started off with solid paper.

Just have to drop it so I don't burn my hands.

And I set it on fire.

And a chemical reaction is currently taking place.

Okay, so it's just gone out now.

So what we're left with is not paper.

It's now ash.

It's really soft, and it's really light, and it comes off on my fingers like this little dust.

So the difference there is that that is a chemical reaction.

We started with solid paper particles, and we ended with a different type of particles.

We now have ash.

That's a different substance.

It's not paper anymore.

A chemical reaction has taken place, and now we have ash.

So let's take a look at a diagram of what's happening in those, with the particles in those reactions.

So here you can see we started with our paper.

And we call what we start with in a chemical reaction the reactant.

So our paper was the reactant.

And you can see what our reactant particles look like.

They're a solid, so they're in that arrangement that we'd expect, regular arrangement close together.

Then when I set it on fire, I cause a chemical reaction to take place.

That's what that arrow is showing, that a chemical reaction is taking place, or a change is taking place.

And I end up with ash.

Okay, the ask in that picture is a bit blacker than my ash, but it's the same substance.

And it's a different substance to our paper.

The particles you can see are a different colour because it's a different substance.

And we call the substance that we end up with in a chemical reaction our product.

So our reactant was paper, and our product was ash.

And the particles are different at the beginning and the end, so that's why we call it a chemical reaction.

Whereas when we looked at melting our ice, that was a physical change.

So we started with our ice, our solid particles, and then they melted.

They changed state, and we ended up with liquid particles.

So in a physical change, the type of particle stays the same, but the substance might change state.

So that's what was happening there, solid to liquid.

That's changing state.

That's melting.

Or another example of a physical change is when something might change shape.

So if I were to take this cardboard matchbox and twist it, I've changed it.

I've changed its shape.

That's a physical change.

But the particles are still the same, okay.

They're still cardboard particles 'cause it's made out of cardboard.

And a third way that we see a physical change occur is when we get two types of particle that become mixed with each other.

So for example, if I were to mix sugar into my water, that would be a physical change.

I'm mixing two types of particle together.

I'm not changing them.

I still have water particles at the end.

And I still have sugar particles at the end.

They're just mixed together.

It is a physical change.

So these, just to recap, are the three types of physical change we have, change of state, change of shape, or mixed together.

Can you just say those with me again and just do them on your fingers? Sometimes saying things out loud helps us to remember them.

So these are our three types of physical reaction.

Number one, change of state, change of shape, and mixed together.

Okay, and those are very different to chemical reaction.

Here are your questions.

So are the following examples chemical reactions or physical changes? Pause the video and answer this question for me now, please.

Great, let's check your answers.

So paper burning is a chemical reaction.

Ice melting is a physical change.

And sugar dissolving is a physical change, okay.

We can also, to help us think about this, physical changes are reversible.

That means we can undo them.

So with my ice melting into water, it's reversible because all I need to do is to put the water back in the freezer or somewhere cold, and it will turn back into ice again.

The same with sugar dissolving.

It's reversible.

One I've mixed my sugar into my water, we learnt that we can separated them again.

We learnt this last lesson.

How do we separate a soluble solid from water? Can you remember? Was it sieving, filtration, or evaporation? Take a moment to think, and say it to your screen.

It was evaporation.

Okay, so that's reversible as well.

Paper burning is a chemical reaction.

That's not reversible.

No matter how hard I try, I can't turn this ash in my bowl back into paper.

Nothing I do will change that.

It's irreversible.

It's a chemical reaction.

The particles have changed.

Okay, next questions.

What happens to particles in a physical change, and what happens to particles in a chemical reaction? Can you pause the video and answer those questions for me now, please? Great, let's check your answers.

So in a physical change, the particles stay the same.

That's the key point.

You might have written that they can get mixed together or change arrangement, but the particles themselves stay the same.

In number two, the particles.

I'm sorry, in a chemical reaction in number two, the particles change from one type of particle to another.

Okay, that's the key there, they change from one type to another, so from paper to ash, for example.

Pause the video and give yourself a tick if you got those right.

If not, take this time, pause it, and correct your answers, please.

Pause the video and do that for me now, please.

Great, okay.

Now we're going to move on to the next part of our lesson, word equations.

I'll tell you what those are.

So scientists represent chemical reactions using word equations.

Scientists always write the reactants, that's what we start with, on the left-hand side of an arrow.

And then they write the products, that's the substances that are made in the reaction, what we end up with, on the right-hand side of the arrow.

So it goes reactants, arrow, products.

And when reading out a word equation, a scientist would say produces rather than the word arrow.

So you wouldn't say paper, arrow, ash.

You'd say paper and heat produces ash.

Okay, so when you see that arrow, you can think or say produces.

What do you think or say when you see the arrow? Produces.

Okay, I'm going to give you an example there, using an experiment that you might know.

So if you have ever made one of those volcanoes or you're familiar with that experiment where you add baking soda or bicarbonate of soda to vinegar, you'll know that it bubbles up.

Okay, if we were to write that as a word equation, it would look like this.

The reactants that we start with are bicarbonate of soda and vinegar.

So you write bicarbonate of soda add vinegar.

It's an equation, so we don't use the word and.

We say the word and, but we write our add symbol, like if we were writing an equation in maths.

We then have our arrow that shows the changes occurring, and then we have our products.

So when these two substances are mixed together, three products are formed, and so the word equation would look like this.

Sodium acetate, water, and carbon dioxide.

Carbon dioxide is a gas.

That's why you see those bubbles when you do this volcano experiment.

So that's what that reaction would be.

So bicarbonate of soda and vinegar produces sodium acetate, water, and carbon dioxide.

Everybody, can you read out this word equation with me? We're going to do it together.

I'm going to one, two, three, and then we'll begin.

And remember, you need to say produces where the arrow is.

One, two, three.

Bicarbonate of soda and vinegar produces sodium acetate, good job, that one's hard, and water and carbon dioxide.

Good job, try it once by yourself.

Great, okay, I've got some more questions for you.

In that reaction we just looked at, what were the reactants, what were the products, and then what goes on the left-hand side of an arrow in a word equation? Is it the reactants or the products? Pause the video and have a go at answering that question now.

If you need to, remember, you can always scroll back, skip back in the video, and watch a part of the lesson again if you need a reminder.

Pause the video and do that for me now, please.

Great, let's check your answers.

Number one, the reactants are what we started with, so bicarbonate of soda and vinegar in that experiment.

Number two, the products are what we end with, so sodium acetate, water, and carbon dioxide.

And then number three, on the left-hand side, we write the reactants.

You might also have written the reactants for this equation, bicarbonate of soda and water, and that's fine as well.

You can give yourself a tick for both of those answers.

So give yourself a tick if you got these correct.

If you need to edit your work, then that's fine.

Just pause the video to give yourself some time to do that now.

Great, next we're going to look at the indicators of a chemical reaction.

An indicator is like a sign.

So when we see or we observe these indicators, then they can give us a clue that a chemical reaction is taking place.

There are five of them.

I'm going to show you a picture that represents each one, and I wonder if you can figure out what it's showing you.

I'll of course tell you what it is, but I wonder if you can figure it out first.

What sign of a chemical reaction do you think this picture might be representing? You can just say it to your screen, think it in your head, or write it down if you want.

So this is showing colour change.

So you can see the colour is changing from red to green, so that's one of our indicators, colour change.

What do you think B might be representing? What about C? I'm going to give you time to think about each one, and then we'll go through the answers at the end.

This one's tricky.

Have a guess.

It's not colour change again.

And then finally, E.

What do you think E is showing you? Okay, let's talk through each one.

So the first one was showing us a colour change.

So sometimes a substance might change colour during a chemical reaction, and actually that did happen in our demonstration at the beginning.

The paper started off as white, and then the ash at the end was black.

A colour change had taken place.

Another sign is an odour or a smell.

If I sniff my living room where I'm filming now, I can actually smell burning from that chemical reaction I did before burning that paper.

Okay, often we will have a smell when a chemical reaction takes place, not always.

Remember, these are five signs of a chemical reaction.

They can give us a clue that a chemical reaction is happening, but it doesn't mean that all five of them happen every single time.

The next one was a temperature change.

So sometimes when a chemical reaction occurs, the substance can become really cold, or it might become really hot, and that temperature change can be a sign.

This was the tricky one.

So in this, two substances are being added together.

Two liquids are being added together.

And a precipitate is forming.

Just practise saying that with me, precipitate.

A precipitate is when a solid is produced inside a liquid during a chemical reaction.

So they're adding two liquids together, but a solid is being produced.

So that bright orange stuff you can see is actually like little parts of a solid being produced, okay.

So a precipitate can be made when two liquids form a solid during a chemical reaction.

And lastly, we have the formation of gas.

So this means that gas is being made, and the sign of that that we're going to see is bubbles.

So you can see the bubbles at the bottom of this.

The bubbles are gas bubbles coming out of the liquid, okay.

So those are our five signs of a chemical reaction.

Can you remember all five? Just take a moment and see if you can count them out on your fingers.

I'm going to remind you in a second.

I'm going to see if I can do it.

Okay, can you remember all five? We've got odour.

We've got the one on the screen, formation of gas, so bubbles.

Temperature change, colour change, and then what was that really tricky one? Formation of a precipitate.

Okay, so if you haven't already, can you please write down those five things on your piece of paper? You might have been doing it as we're going> Because we're going to need them for the next section.

So actually I'm just going to go back and give you a chance to do that.

You've already written them down, then you can just skip to the next part of the video that says investigation, okay? So colour change.

Pause the video and write that down.

Odour.

Pause the video and write it down.

Temperature change.

Pause the video and write it down.

Formation of a precipitate.

Pause the video and write that down you might also want to write a note to yourself about what that means, so solid produced in a liquid.

And lastly, formation of gas bubbles.

Okay, great, now we've got those written down, let's move on to our investigation.

So what I would like you to do, please, we're just going to do a really simple investigation today.

We're just going to investigate one thing.

I'm going to demonstrate this for you.

So if you don't have these things at home, that's okay.

You can watch my demonstration.

If you do have these things, then you're more than welcome to take part too.

So before we begin, I need you, please, to draw this table on your piece of paper.

So you've got a reactants column, an observation column, and a chemical reaction or physical change question mark column.

Pause the video and draw this table for me now, please.

Great, okay.

So these are the steps that we're going to follow.

We're going to take two teaspoons of sodium bicarbonate, bicarbonate of soda in a cup.

Then we're going to fill that cup 1/4 full with vinegar.

And then we're going to look at the reaction and write down our observations.

So if I just flick back to this table, we're going to write down your observation.

What do you see when you add the sodium bicarbonate to the vinegar? And then I want you to check those observations.

Do you notice any of those five signs of a chemical reaction that we wrote down before? If you do, then you can write in the next column that it's a chemical reaction.

If you don't notice any of those things, then you can write that it's a physical change, okay.

If you have these things, if you have vinegar and you have sodium bicarbonate, then you can pause the video here, and you can have a go at doing this yourself because it can be more fun to try yourself before you watch me do it.

If you don't have these things or you'd like to watch me do an example first, then that's okay.

I'm going to do that for you now.

Okay, so I've got my cup, and the first instruction on my method was to put two teaspoons of bicarbonate of soda in.

So I've got my bicarbonate of soda here.

It's a white powder.

If you don't have bicarbonate of soda at home, you could also use baking powder, okay.

These are things that you or your parents, your adults at home might cook with.

If not, don't worry 'cause you're going to watch me, and you'll still get to see it.

So I'm going to put two teaspoons into my cup like this.

And just put a little extra 'cause I spilled some.

And then it says to fill your cup 1/4 full, so to about there, with vinegar.

So I'm going to do that next.

I've got my vinegar.

And I'm going to fill the cup.

When this happens, you need to watch what happens and write down your observations in the table.

You're looking for any of those five signs of a chemical reaction.

What can you see is happening? Write down your observations.

There you go.

So that is the basis of the volcano experiment.

So if you wanted to make a model volcano, then that's often what's used to make the lava.

So in your table, you should've written what you saw there.

And you saw quite clearly bubbles being produced, so the formation of gas.

So does that mean it's a chemical or a physical change? Can you write that in your table in the last column for me, please? It's a chemical change, okay.

Now, would you please answer these questions for me? So what evidence do you have to support the conclusion that a chemical reaction took place? So how do we know that a chemical reaction took place? You can write down what your observations were.

And then your second question is in another reaction, lead nitrate was added to potassium iodide.

Don't worry if you haven't heard of those chemicals before.

Just think about what the question's asking you.

A yellow solid was formed.

Is this a chemical or a physical reaction? So both lead nitrate and potassium iodide are liquid, and when they're added together, a yellow solid is formed.

Is this a chemical or physical reaction? How do you know? Pause the video and answer these questions for me now, please.

Great, let's check our answers.

So you might have written for number one something like this.

When sodium bicarbonate was added to vinegar, I observed bubbles, which indicates that a gas is being produced.

This is evidence of a chemical reaction.

And then for number two, this is a chemical reaction as or because a solid precipitate was formed.

Well done if you got those correct.

I would like everybody now to take the opportunity to make your answer better.

So even if you got the right answers, we can always improve our answers by changing our wording to sound more scientific, like adding a bit more detail in or making sure that we've got full sentences.

So can you pause the video, and can you use what's on the screen, please, to edit your answer and make it even better? Fantastic.

That brings us to the end of the lesson.

Well done for all of your hard work today.

I'm really proud of all you've accomplished.

If you'd like to share your work with someone, then maybe go and show your work to the adult in your house.

And if you'd like, you can ask your parent or your carer to share photos of your work on Twitter with the hashtag #LearnWithOak or #ONAscience.

I hope you enjoyed today's lesson and that you have a fantastic rest of your day.

I will hopefully see you back here soon for another science lesson.

Bye, everybody!.