Lesson video

Hello, I am Mrs. Adcock, and welcome to today's lesson on carboxylic acids and esters.

We are going to be looking at what are carboxylic acids and some of the reactions of carboxylic acids.

Then we are going to move on to think about what are esters and where are esters used.

Today's lesson outcome is, "I can describe the structure of the first four carboxylic acids and recognise and describe reactions where carboxylic acids are involved." Some of the keywords we will be using in today's lesson include carboxylic acids, weak acids, carbonate, esters, and ethyl ethanoate.

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

It would be a good idea to pause the video now and read over those sentences.

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

Today's lesson on carboxylic acids and esters is split into three main parts.

First of all, we are going to be looking at carboxylic acids and we have an introduction to carboxylic acids.

Then we're going to move on to look at the reactions of carboxylic acids before finally looking at esters.

Let's get started on the first part of our lesson on introduction to carboxylic acids.

Carboxylic acids are a homologous series of compounds that contain the COOH functional group.

Here is a model of the simplest carboxylic acid.

You can see this simple carboxylic acid contains one carbon atom and it contains that COOH functional group, which is split into a carbon with a double bond to an oxygen, and then also attached to that carbon is an OH group.

Here is the COOH functional group of carboxylic acids.

Citric acid is a carboxylic acid that's found in fruits such as lemons.

So we can see an image there of some lemons, and we can see a molecule of citric acid.

That citric acid molecule looks very complicated, but we can identify it as a carboxylic acid by finding those COOH functional groups that all carboxylic acids contain.

There they are highlighted for you.

Time for our first question, "Which functional group is present in carboxylic acids?" Is it A, a carbon-carbon double bond; B, COOH; or C, an OH? The functional group present in carboxylic acids is a COOH.

And remember, the functional group is the atoms or group of atoms that are responsible for the way a compound reacts.

A shows the functional group of alkenes, and C shows the functional group of alcohols.

When naming carboxylic acids, they have the suffix -oic acid.

The first four carboxylic acids in the homologous series are methanoic acid.

This is our simplest carboxylic acid.

It has that COOH, our functional group.

And then remember that each carbon atom can only form four covalent bonds, so that remaining covalent bond bonds to a hydrogen atom.

And you will notice when looking at the name that this carboxylic acid ends in -oic acid, so it's methanoic acid.

Here we've got the second carboxylic acid in the homologous series, and that's ethanoic acid.

So it starts with eth because we've got two carbon atoms there, and then it ends in -oic acid.

You can see there that we've got the structural formula for ethanoic acid.

It's a CH3, and that's bonded to a COOH.

Next we have propionic acid.

So prop, because we've got three carbon atoms. Here you can see the structural formula for propanoic acid is CH3CH2COOH.

And hopefully you can think what might be coming next.

It's gonna be a carboxylic acid that will have a chain length of four carbon atoms, and it's gonna have that COOH functional group.

We've had methanoic acid, ethanoic acid, propanoic acid, and the next carboxylic acid in the homologous series is butanoic acid.

Butanoic acid contains four carbon atoms, and again, hopefully you can spot that COOH functional group of carboxylic acids.

Time for another check for understanding.

The image shows a molecule of: is it A, methanol; B ethanol; C, methanoic acid; or D, ethanoic acid? The correct answer is D, ethanoic acid.

Methanol and ethanol are both alcohols, so these would just have the functional group OH, whereas this molecule, it has an OH, but it also has that carbon double bond to oxygen as well as part of the functional group.

So the functional group here is COOH, which means it's a carboxylic acid.

It contains two carbon atoms, so it will be ethanoic acid.

Another question for us to have a go at.

"What name is given to the carboxylic acid containing three carbon atoms?" And it would have the formula C2H5COOH.

Is it A, butanoic acid; B, methanoic acid; C, propanoic acid; or D, ethanoic acid? The correct answer is C, propanoic acid.

A, butanoic acid would contain four carbon atoms. Methanoic acid would contain only one carbon atom, and ethanoic acid contains two carbon atoms. So well done if you correctly identified that propanoic acid contains three carbon atoms. Carboxylic acids dissolve in water to produce solutions that are weakly acidic.

Weak acids partially dissociate to produce H+ ions when in solution.

And we've got an example here showing ethanoic acid and when it's added to water, so when it's in solution, it will partially dissociate, and that's why we've used that reversible reaction symbol there.

We can see when it's added to water, how it can dissociate to form those H+ ions.

Carboxylic acids are weak acids because they partially dissociate.

We have the formula there at the bottom.

So ethanoic acid is CH3COOH, and that will form this ion, which is CH3COO, and that's got a negative charge and a H+ ion.

Weak acids, such as carboxylic acids, have higher pH values than stronger acids with the same concentration.

If we look at our pH chart here, we can see that neutral solutions will have a pH of seven, and alkalis have a pH ranging from 8 to 14.

And acids will have a pH somewhere between zero and six.

Carboxylic acids are weak acids, so you will notice that they will have higher pH values than strong acids with the same concentration that will have a lower pH value.

This chart also shows us the colours that we would expect when we add our acids or alkali or neutral solutions to universal indicator.

For carboxylic acids, we would expect to see an orange or yellow colour when they're added to universal indicator.

Time for another check for understanding.

"Carboxylic acids are weak acids that fully dissociate in solution to produce H+ ions." Read that statement again carefully and decide whether you think it is true or false.

That statement is in fact false.

Can you justify your answer? Is it false because, A, carboxylic acids are strong acids that fully dissociate in solution to produce H+ ions? Or is that statement false because, B, carboxylic acids are weak acids that partially dissociate in solution to produce some H+ ions? The correct answer is B.

So carboxylic acids are weak acids, and they do not fully dissociate.

They partially dissociate to produce some H+ ions.

Time for first practise task of today's lesson.

And for this practise task, you need to complete the table.

In the first row, you need to fit in the carboxylic acid name, so you've got other clues to help you work out the names.

Then in the second row you need to write out the structural formula.

And if you notice here when we are writing out the structural formula, we show how those atoms are arranged in the molecule, and you've got two examples there done for you.

And in the final row, you need to draw out the displayed formula, and when you draw out the displayed formula, you will show all the covalent bonds present in the molecule.

Good luck completing this task.

If you pause the video now, have a go, and come back when you're ready to go over the answers.

If we look in the first column, the structural formula there is for methanoic acid, and your displayed formula should look similar to this molecule here.

Ethanoic acid has the structural formula CH3COOH.

And the displayed formula should look similar to this where you've got two carbon atoms, and make sure that each of your carbons has formed only four covalent bonds.

The final two columns, we've got the displayed formula here, and that's the displayed formula for propionic acid, which has the structural formula CH3CH2COOH.

And in our final column we've got butanoic acid, and the displayed formula should look similar to this one that you can see now.

Well done if you correctly identified the names, the structural formula, and you drew the correct displayed formula for those molecules.

The second question in this task is to show what happens when each of these carboxylic acids is added to water.

So you've got two carboxylic acids there, they're gonna be added to water.

We've got that reversible reaction symbol because these will partially dissociate.

You need to draw the products to show what happens when each of these carboxylic acids is added to water.

Pause the video now, answer this second question, and then we'll go over the answers.

For A, you should have drawn this negative ion, and then you'll have the positive H+ ion.

And for B, you'll have C3H7COO-, that's got a negative one charge.

And then we have the hydrogen which has a positive one charge.

We've finished the first part of today's lesson on an introduction to carboxylic acids.

Let's move on now to look at how these carboxylic acids can react.

Carboxylic acids can be formed from the oxidation of alcohols using oxidising agents.

An example showing the oxidation of ethanol.

So this is showing us how we can form carboxylic acids from alcohols.

So we've got an alcohol there, we can see that's ethanol with two carbon atoms. And we can see the OH which is the functional group in alcohols.

This is going to be oxidised in the presence of an oxidising agent, and we form a carboxylic acid.

And the carboxylic acid we form in this case will be ethanoic acid 'cause we start with ethanol and we can oxidise that to ethanoic acid, which is a carboxylic acid.

Here's a question to have a go at.

"Propionic acid can be produced from the oxidation of:" Do we oxidise, A, ethanoic acid; B, butanoic acid; or c, propanol if we want to form propanoic acid? The correct answer is C propanol is an alcohol and that can be oxidised by an oxidising agent to form propanoic acid.

Well done if you chose answer C.

Carboxylic acids can react with metal carbonates to produce salt, water and carbon dioxide.

So metal carbonates react with acids to produce salt, water and carbon dioxide.

And because carboxylic acids are weak acids, then you can see we produce the same products.

We also produce salt, water and carbon dioxide.

The word equation for this reaction is metal carbonate plus carboxylic acid, and they react together to produce salt plus carbon dioxide plus water.

An example of a reaction between a metal carbonate and carboxylic acid is sodium carbonate, that's our metal carbonate, can react with methanoic acid or carboxylic acid.

And these are going to produce a salt plus carbon dioxide plus water.

And in this case our salt will be sodium, so the name of the metal, sodium methanoate.

And that methanoate part comes from the carboxylic acid.

Here we can see a reaction between a metal carbonate and carboxylic acid.

We have a carboxylic acid in the beaker, and to that we are adding a metal carbonate.

These will react together to produce a salt and carbon dioxide and water.

And we can tell we are producing a gas, in this case, carbon dioxide because of the effervescence we can witness there.

Looking at the displayed formula helps us to see how that salt forms. We can use our example here of sodium carbonate reacting with methanoic acid to form sodium methanoate and carbon dioxide and water.

Underneath that, we have got a balanced symbol equation.

And if you look towards the bottom of your screen, you can see that we have our sodium carbonate and methanoic acid.

And when these react together, the sodium has now bonded with part of our methanoic acid to form that salt, sodium methanoate.

We form carbon dioxide, and those atoms have come from the carbonate.

And then our final product, water, is formed because of the oxygen from the carbonate and the hydrogen that's been released from the carboxylic acid.

"Which gas is produced when carboxylic acids react with metal carbonates?" Do you form A, oxygen; B, hydrogen; or C, carbon dioxide? The correct answer is C, carbon dioxide.

So when a metal carbonate reacts with a carboxylic acid, we form a salt plus water plus carbon dioxide gas.

Carboxylic acids can also react with alcohols.

And when they do this in the presence of an acid catalyst, you'll form esters.

We've got the word equation written there for us.

An alcohol reacts with a carboxylic acid in the presence of an acid catalyst to form an ester plus water.

Here we've got an example of a carboxylic acid forming an ester.

We've got methanol, that's our alcohol, plus propanoic acid, which is a carboxylic acid.

These react together in the presence of an acid catalyst to form methyl propanoate, and that's our ester plus water.

We've got our alcohol and a carboxylic acid forming our ester plus water.

Time for quick check for understanding.

"When a carboxylic acid reacts with an alcohol in the presence of an acid catalyst, which organic compound is produced?" And an organic compound is a carbon-based compound.

Will it be A, a haloalkane; B, an alkene; C, an ester; or D, an alcohol? The correct answer is C, an ester.

When a carboxylic acid reacts with an alcohol in the presence of an acid catalyst, we will form an ester and water.

Well done if you choose answer C.

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

You need to identify which of these molecules are carboxylic acids.

And remember, the carboxylic acids contain the functional group COOH.

Pause the video.

Now look carefully each of those molecules.

You've got a mixture between structural formula and displayed formula.

Identify the carboxylic acids, and then come back when you're ready to go over the answers.

For question two, you need to complete the following equations.

If you pause the video now, have a go at this question, and I'll see you back in a moment.

Question one, identify which of these molecules are carboxylic acids.

You should have C, D and G.

So well done if you identified those three carboxylic acids.

They all have the COOH functional group, which none of the other molecules contain.

Question two, complete the following equations.

In A, we have sodium carbonate that's going to react with methanoic acid to produce our salt there, which is sodium methanoate plus carbon dioxide plus water.

In B, it would be calcium carbonate, and that will react with propanoic acid to form calcium propanoate, which is our salt, and carbon dioxide and water.

And in C, we have an alcohol that reacts with carboxylic acid in the presence of an acid catalyst to produce an ester and water.

And in D, we have the opportunity to try and name our alcohol here.

We are forming the ester ethyl ethanoate.

So our alcohol is ethanol.

Well done if you got that one correct.

Plus ethanoic acid, and these react together to form the ester there ethyl ethanoate and water.

Some tricky questions there.

So well done for having a go, and hopefully you got most of those correct.

It's time for us to move on to the final part of our lesson on esters.

Esters can be synthetic or found naturally.

They are found naturally in many fruits.

We've got an image there showing strawberries, and strawberries are an example of a fruit that contain esters.

Esters are used in foods as flavouring and in perfumes due to their sweet smell.

So we've got image there of some perfume containing esters as well.

Esters contain the functional group COO, and it looks like this.

So you can see an example there of an ester.

We have that COO functional group.

Esters can be produced from reacting together an alcohol and a carboxylic acid in the presence of an acid catalyst.

Here we've got an example.

We have an alcohol which has that OH functional group.

We are going to react that with a carboxylic acid.

And our carboxylic acid contains that COOH functional group.

And when these react together, they form an ester and water.

Here we can see that part of our ester came from the alcohol.

And then the other part of our ester, which contains that C double bond O, came from the carboxylic acid.

And the hydrogen was removed from our alcohol, the OH group was removed from our carboxylic acid, and these bonded together to form our other product, which was water.

"To produce an ester, what does a carboxylic acid react with?" Is it A, an alkane; B, a metal carbonate; C, an alcohol; or D, water? To produce an ester, a carboxylic acid will react with an alcohol.

And they react together in the presence of an acid catalyst to produce an ester and water.

Well done if you choose option C, alcohol.

When naming esters, we take the alcohol part first and this ends in -yl.

And then we take the carboxylic acid part and this ends in -oate.

Here we have an example.

We've got the alcohol ethanol, and this is going to react with the carboxylic acid, propanoic acid, and these react together to form our ester and water.

And the name of our ester is ethyl, and that came from the name of the alcohol, ethanol.

So we changed that into ethyl.

And then we have propanoate, which came from our propanoic acid.

So we changed the name of our carboxylic acid.

It has the ending -oate.

So we end up with the ester, ethyl propanoate.

Let's look at another example.

Butanol is our alcohol, and this is going to react with methanoic acid.

So we take the name of the alcohol first, and we put the ending -yl.

So we have butyl, and then we have the carboxylic acid part, and this ends in -oate.

So we have butyl methanoate, and our other product is water.

Here we have another example, and this time we are going to practise naming the esters when we've been given a displayed formula showing the molecule.

This ester is called ethyl ethanoate.

Here we can see the ethyl part because this would've come from the alcohol ethanol.

So ethanol, when it reacts with a carboxylic acid, will give us an ester that starts with ethyl.

And this part would've come from the carboxylic acid.

And if we look, it contains two carbon atoms. So this would've been ethanoic acid.

So ethanoic acid would've react with ethanol to produce the ester ethanoate.

What is the name of this ester? Look carefully at the part that's come from the alcohol and the parts that has come from the carboxylic acid, and see if you can name this ester.

Is it A, propyl methanoate; B, methyl propanoate; or C, ethyl ethanoate? The name of this ester is methyl propanoate.

If you look at the first part of that molecule, you can see it contains one carbon atom, and that would've come from a molecule of methanol.

So we know that this ester's gonna start with methyl.

Then if we look to the other part of the molecule that contains the carbon double bond O, this would've come from our carboxylic acid.

This contains three carbon atoms, so it would've been propanoic acid before it reacted with our methanol, and therefore it forms the ester methyl propanoate.

Well done if you've got that difficult question correct.

Time for our final practise task of today's lesson, and this is on esters.

Question one, ethanoic acid reacts with ethanol in the presence of concentrated sulfuric acid.

What is the role of the concentrated sulfuric acid? Can you draw the displayed structure of the ester that forms? Can you name the ester formed? And finally, what is a possible use of this ester? Pause the video now, have a go at answering this question, and then come back when you're finished.

Let's go over the answers.

The role of the concentrated sulfuric acid is that it acts as a catalyst, the displayed structure of the ester.

Your image should look similar to that one there.

Just check your number of carbon atoms. Check that you've drawn that functional group for the ester correctly, and check that each of your carbon atoms has only formed four covalent bonds.

When we name this ester, it'll be ethyl ethanol.

We know this because it was produced from ethanol and ethanoic acid.

And a possible use of this ester, your answer may include that we could use esters in perfumes or as flavourings in food.

Well done if you got those questions correct.

We have covered a lot in today's lesson, so well done for focusing well.

Let's just summarise some of the key points we have covered on carboxylic acids and esters.

Carboxylic acids have a COOH functional group.

Carboxylic acids are weak acids.

When ethanol, which is an alcohol, is oxidised, a carboxylic acid, and in this case, ethanoic acid is formed.

Carboxylic acids react with carbonates, and when they do this, they produce a metal salt, carbon dioxide and water.

Carboxylic acid can react with alcohol in the presence of an acid catalyst to produce esters such as ethyl ethanoate.

I hope that you've enjoyed today's lesson, and I hope that you're able to join me for another lesson soon.