Hello, my name's Mrs. Clegg.

Welcome to our lesson today.

We'll be learning more about decomposition, which is a chemical reaction, and this is part of the unit Understanding chemical reactions.

Anyway, let's get on.

And here's today's outcomes.

So by the end of this lesson, you should be able to describe what happens during decomposition reactions, you should be much more comfortable in knowing what a decomposition reaction is, and you should be able to write chemical equations to show these.

And we'll be looking at both word equations and symbol equations.

Here are the key words today that I want you to listen out for, decompose and decomposition.

And here they're written into a sentence.

When a substance decomposes, it undergoes a decomposition reaction.

And a decomposition reaction is a type of reaction in which a reactant compounds breaks into two or more products.

Today's lesson is broken into two parts.

We're going to first of all look at the decomposition reactions and then we'll look at investigating a metal carbonate decomposing.

So let's get started with decomposition reactions.

Sometimes, one reactant produces more than one product.

And the breakdown of a compound into simpler substances is called decomposition.

Let's look at copper carbonate.

If you notice, copper carbonate is a lovely green coloured powder.

It's heated.

Nothing else is added.

So it's heated, and it turns into a black solid there with gas given off.

This is thermal decomposition.

So heat is being used to break down the copper carbonate.

And here's the word equation.

So copper carbonate is changed into copper oxide and carbon dioxide.

Copper carbonate's the reactant and copper oxide and carbon dioxide are all products.

When metal carbonates decompose upon heating, they typically form metal oxides and carbon dioxide gas.

When calcium carbonate undergoes thermal decomposition, it produces calcium oxide and carbon dioxide gas, and calcium oxide is a metal oxide.

Now, decomposition reactions commonly are started by heat, as in the case of calcium carbonate and copper carbonate we've just looked at, but light or electricity can also be involved.

The input that starts the chemical reaction is often included in the chemical equation over the top of the arrow.

So if we look at our acquired equation at the top there, we've put heat there 'cause it's thermal decomposition.

Some substances undergo decomposition reactions when electricity's applied.

So water can be broken down using electricity to produce hydrogen and oxygen.

We put electricity across the top of the arrow there.

And here's the balance chemical equation, and something's missing, electricity over the top of the arrow.

Well done for remembering that.

Now, other substances undergo decomposition reactions when light is present.

And here's hydrogen peroxide.

And you might notice it's being capped in a brown glass bottle.

And that's deliberate to try and prevent the hydrogen peroxide breaking down when light is present.

So here's the reaction.

Hydrogen peroxide breaks down under the presence of light to produce water and oxygen.

And here is our chemical equation, and it's balanced.

So which of these best matches the description of a decomposition reaction? Well done.

One reactant breaks down to form two or more products.

So hydrogen peroxide was the only reactant, and it broke down to produce water and oxygen.

Let's have another question.

So true or false.

The only way to start a decomposition reaction is to shine a light on the reactant.

Is that true or is that false? Well done if you said false.

And what's the justification? So which one of these two statements would you use? And the answer is, of course, A, a decomposition reaction can also start by heating the reactant or by passing an electrical current through the reactant.

Well done.

Let's look at Task A.

So we've got some statements coming up from pupils, and what I'd like you to do is to correct those pupils' statement.

We've got three students.

Can you correct their statements? Pause the video and come back when you are ready.

So let's have a look at the answers.

So for Jacob, we changed two compounds reacting into a single compound breaking down to form two or more products.

Well done if you got that.

Let's have a look at Jun.

So decomposition reaction usually require something light or something to occur.

So what were the answers? Heat or electricity.

Well done.

And then Sofia's answers, when metal carbonates decompose upon heating, they typically form metal oxides and carbon dioxide gas.

Brilliant if you've got those right.

Let's move on to the second part of our lesson, investigating metal carbonate decomposition.

So metal carbonates undergo thermal decomposition at different rates.

Let's have a look at copper carbonate again.

And you can see that that decomposes quite quickly to produce the black copper oxide and carbon dioxide gas.

Now, the longer it takes to decompose, the more stable the metal compound is and the stronger the bonds are between the metal and the carbonate.

Let's remind ourselves of the equation for this reaction.

So copper carbonate changes to form copper oxide and carbon dioxide.

And we can actually test carbon dioxide using lime water.

So let's have a look at this test.

What do we have to do? We bubble the gas through lime water, and the lime water changes from being colourless to cloudy and white.

If it stays colourless, if the lime water remains colourless, then the gas is not carbon dioxide.

And here we've got some carbon dioxide being bubbled through lime water there.

It's clear at the start.

And you can see the lime water is going cloudy.

Let's do a quick check.

So lime water has had carbon dioxide bubbled through it, and it has changed from colourless to.

Which of these is the correct answer? Well done if you said white.

Now, let's look at some equipment that we would use to see how easily metal carbonates undergo a decomposition reaction.

Remember, the longer it takes to decompose, the more stable the metal compound is and the stronger the bonds are between the metal and the carbonate.

So we've got a boiling tube here, we've got a clamp and stand, we've got the metal carbonate, we've got a Bunsen burner, a heat resistant mat, a bung in the top of the boiling tube, and a delivery tube so that the gas can bubble through lime water.

So have a look at that equipment and familiarise yourselves with the names.

And when you are ready, move on to the next question.

What part of the equipment transports the gas produced to the lime water? Which one of those is it? Well done if you said delivery tube.

Now, name the equipment used to heat the metal carbonate.

Which of those would you use? Well done if you said Bunsen burner.

So let's have a look at Task B now.

This task involves carrying out an experiment to see how stable metal carbonates are.

In chemistry, that word stable means that a substance is not particularly reactive.

So if we say something is stable, it's not reactive.

If it was unstable, it's very reactive.

We can measure how stable a metal carbonate is by heating it and bubbling the carbon dioxide given off through lime water.

The faster the lime water goes milky or cloudy or white, then the faster the rate of decomposition.

So here's the equipment that I showed you earlier.

Could you still label it? You might like to pause the video and check.

The method for the experiment is broken down into steps.

So step one, place a large spatula of a metal carbonate into the boiling tube.

The spatula is a piece of lab equipment which we use to transfer powder or small granules.

It might have a flat end or a scoop, a bit like a spoon.

And first of all, I'd like you to observe and record the colour of the metal carbonate into your table.

Step two, we place the bung with the delivery tube into the boiling tube, and make sure the other end of the delivery tube is in the test tube under the level of the lime water.

And this is really important so that the carbon dioxide gas bubbles through the lime water.

Step three, I'm gonna heat the metal carbonate gently at first and then strongly.

Observe and record any colour changes into your table.

Step four, we're gonna observe and record the lime water colour to identify if carbon dioxide gas is released.

Remember, lime water is colourless at the start, and if carbon dioxide is present, it will turn cloudy or we might call it milky or white.

If it stays colourless, then carbon dioxide is not present.

And step five, we'd repeat the same experiment with the other metal carbonates we want to test.

And each time we would change the lime water so it's fresh.

We're also going to record how easy it was to get the metal carbonate to decompose and produce carbon dioxide.

Here's a results table that you could use.

So we've got the metal carbonates on the left hand side, colour before heating, colour after heating, gas bubbles observed, that's a yes or no, and how easy was it for the metal carbonate to break down.

So pause the video and come back when you've carried out the experiment and completed your results table.

Okay, how did you do? Let's have a look at the results and see if they're similar to mine.

So copper carbonate is a lovely green colour before heating.

Afterwards it goes black.

We definitely saw gas bubbles observed.

And it was very easy to decompose.

Lead carbonate is white, and it goes yellow after heating.

We definitely saw bubbles, and it was easy, but maybe not as easy as the copper carbonate.

Zinc carbonate, it was white beforehand, and then it was yellow when it was hot, and it was white when it cooled down.

Did you notice that? You saw bubbles, and yes, it was quite easy.

So how did you do with sodium carbonate? It was white before heating and white after heating.

And there was no gas bubbles seen.

The sodium carbonate did not decompose.

There was no reaction.

And potassium carbonate was also white before and white afterwards.

No gas bubbles seen, so it didn't decompose.

So using your results, could you write a conclusion for your experiments? And you could use this sentence starter.

The least stable metal carbonate was, and I know this because I observed what? The most stable metal carbonate was, and I know this because I observed what? So pause the video and come back when you've completed those.

Okay, let's have a look at the answers.

The least stable metal carbonate was copper carbonate.

And I know this because I observed carbon dioxide was produced quite quickly, the lime water changed colour quickly, and the copper carbonate changed from green to black quickly.

So a great answer would have all of those observations.

The most stable metal carbonate was sodium carbonate or potassium carbonate or both.

And I know this because I observed carbon dioxide was not produced.

The lime water did not change colour.

And no colour change of the carbonate was observed.

Well done.

Let's have a look at question three.

So see if you can write word equations for the reactions that did occur, and then write symbol equations for the reaction that occurred, and include their states of matter.

Use the information in the table I've given you below.

So we've got the compound name and the compound formula to help you.

So question three, write word equations.

And question four, write symbol equations.

And don't forget the states of matter.

Pause video and come back when you are ready.

So how did you do? Let's have a look at the answers.

So copper carbonate decomposers with heat to form copper oxide and carbon dioxide.

Lead carbonate decomposes with heat to form lead oxide and carbon dioxide.

Zinc carbonate decomposes with heat to form zinc oxide and carbon dioxide.

So let's have a look at the symbol equations now.

And don't forget those states of matter.

You might like to pause the video and check your answers.

So there's copper carbonate.

It's a solid.

It's decomposed by heat to produce solid copper oxide and carbon dioxide gas.

And there's the answer for lead carbonate and for zinc carbonate.

So pause the video, if you need to, to check your answers.

So we've come to the end of the lesson now.

So let's have a quick look at the summary of our learning today.

So decomposition reactions involve a single compound breaking down into two or more products.

So remember we looked at copper carbonate, we've looked at zinc carbonate, lead carbonate.

So they were all single compounds that then broke down into two or more products.

So decomposition reactions usually require heat, light, or electricity to occur.

Remember the light with hydrogen peroxide that was kept in a brown bottle? Can you remember why? And you've looked at thermal decomposition.

That was decomposition using heat.

And remember, electricity can actually break down water into hydrogen gas and oxygen gas.

And then finally, when metal carbonates decompose upon heating, they typically form metal oxides and carbon dioxide gas.

And we worked out that we can test for the carbon dioxide gas using lime water, which is colourless and that goes cloudy or milky or white when carbon dioxide is present.

So well done.

I look forward to working with you again next lesson.