Lesson video

Hello, my name's Mrs. Clegg.

Welcome to today's lesson, which is all about salts.

We're gonna learn what a salt is, and also we'll look at how they're formed, as well as being able to work out their formula.

This is part of the unit called making salts.

So let's begin our lesson.

Here's our learning outcome for today.

So by the end of the lesson, I hope you'll feel much more confident in being able to describe salts and work out their empirical chemical formula from diagrams, as well as being able to give ionic descriptions of acids and alkalies.

Here are today's keywords that I want you to listen out for.

So salt, empirical formula, acid, base, and neutralisation.

You might want to pause the video right now and take some notes so that you can refer back to these words and definitions throughout the lesson.

Today's lesson is split into two parts.

We're going to look at the composition of salts first of all, and then we'll look at how we form them.

So let's get started with the first part of our lesson.

Now, salts have lots of uses.

Sodium chloride you will have come across.

We often call it table salt.

We use it as a flavouring.

And there's a picture of sodium chloride crystals there.

And you can see it's a solid, so don't forget the state symbol in brackets.

And we also use salt, usually rock salt, to spread on icy roads and paths to help melt the ice.

That's still sodium chloride, it's just less pure.

There are many other salts as well with lots of other different uses.

So ammonium carbonate is used as smelling salts.

Calcium sulphate, those of you that have broken bones, it's used in making plaster casts.

Iron sulphate, if you've ever had anaemia, you might have taken iron tablets, which would be tablets made of iron sulphate salt.

And then we also use a mixture of salts in fertilisers.

So lots of different uses there.

Let's have a look at salts in a little bit more detail now.

So they're all made of positive metal ions and negative non-metal ions held together by ionic bonds.

Here we've got potassium chloride.

Now remember, potassium is in group one, so that means it has one electron on the outer shell and it donates that electron to form a positive stable metal iron.

And the chloride ion is a halogen group seven.

So it has seven electrons on the outer shell, so it gains an electron to become a stable negative ion, and they're held together by ionic bonding.

And an ionic bond is the strong electrostatic force of attraction between the positive and the negatively charged ions.

Let's have a look at magnesium chloride here as well.

So we've got magnesium.

Remember that's in group two, so it donates two outer electrons to each of the chloride ions here.

So we've got a magnesium is a 2+ ion and each of the chlorides is a negative ion.

And here we've got the ionic bonding between magnesium and the two chloride ions.

The electrostatic force of attraction between the negative and the positive ions acts in all directions, and that creates this 3D lattice, a giant 3D lattice structure, of these alternative positive and negative ions.

So here we've got potassium and chloride ions.

The purple represents the potassium ions and the green are the chloride ions.

And as more ionic bonds form, crystals of the salt develop.

And we can see some crystals of the white potassium chloride there.

Remember that would be called a metal halide as well.

Let's have a quick check.

A salt is composed of one positive ion and one negative ion.

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

Now can you explain your answer? So pause the video and come back when you've got an explanation as to why that statement is false.

Welcome back.

So you might have written something slightly different, but salts are formed from many positive and negative ions forming a 3D lattice crystal.

As there is no definite number of each ion in a salt, its chemical formula is the same as its empirical formula.

A salt's empirical formula provides the ratio of its positive metal ions to its negative non-metal ions.

So it's basically the simplest whole number ratio of atoms in a compound.

So for every potassium ion in the lattice, there is one chloride ion.

And so the ratio of potassium ions to chloride ions is 1:1.

And so the chemical formula for potassium chloride is KCl.

Let's have a quick check here then.

What is the chemical formula for magnesium sulphate? The magnesium 2+ ions are the green spheres and the sulphate 2- ions are the red spheres.

Well done if you said d.

And the ratio of magnesium ions to sulphate ions is 1:1.

The ratio of ions in a salt ensures that the overall charge of the salt is zero.

In other words, the positive and the negative ions balance out.

So if the charges of the positive and negative ions are the same, the ratio will always be 1:1.

So here we've got lithium fluoride, so lithium + fluoride -, that's a 1:1.

And so the formula is LiF.

Don't forget to make sure you've got the symbols correct.

So lithium is L, capital L, and lowercase i and fluoride would have a capital F.

Let's have a look at another example.

So here we've got calcium 2+ ions and sulphate 2- ions.

So what will the ratio be here and what will the formula be? So the ratio is 1:1.

We've got a 2+ and a 2-, so they cancel each other out really.

And so the formula is CaSO4.

Let's have a look at different one.

So NH4, those are ammonium ions, NH4+, and nitrate, NO 3-.

So let's have a look at the ratio of ions.

It's one plus to one negative, so 1:1.

So the formula is NH4NO3.

And don't forget to make sure that those numbers are subscript.

That's really important.

If the charges of the ions in the salt differ, then the ion ratio can be determined using a calculation grid and the charge of each ion.

So here is one way of doing it.

So calcium bromide contains calcium ions, calcium 2+, and bromide ions, Br-.

So here is a calculation grid that might help you.

So we put the charge value, so that we know calcium has a charge of 2+, bromide has a charge of 1-.

Put those in there.

And then we look to see which ion has the highest charge value, so that would be calcium, and assign that ion a ratio of one.

So we put one there for calcium ions.

And then what we do is multiply the ratio by the charge to find the overall charge for the calcium 2+ ions.

So it's two.

And then to find out about the bromide ion, we know that the total charges must balance, we know that, so the total charge for calcium must balance that for the bromide.

So we can put a two there.

We divide the total charge in the bromide ion column by the ratio value.

So two divided by one is two, and that gives us the ratio.

So there is one calcium to two bromide ions, and so the formula therefore is CaBr2.

We'll go through this again with another couple of examples, so don't worry if you haven't got it yet.

So a salt is composed of ammonium ions, NH4+, and sulphate ions, SO4 2-.

What is its empirical formula? So let's put the grid up.

So what's the charge value on the ammonium ion is one, and for the sulphate it's two.

So remember then we look for the ion with the highest charge value, so that would be the sulphate ion and we allocate that to one in the ratio.

Then we multiply the ratio by the charge value and put that in the total charge box.

We know that the total charge on the ammonium ions must be the same as the sulphate ions.

So we can put a two here.

And then we divide the total charges by the charge value there, and that is our ratio.

So we know we need two ammonium ions for every sulphate iron.

And we do that by putting the ammonium ions in brackets to show that there's two of them, otherwise it would get a little bit complicated.

So let's have a look at another example.

So I'm going to put one up now, and I want you to have a go and then we'll go through the answer in a moment.

So here's the statement.

A salt is composed of potassium ions, K+, and phosphate ions, PO4 3-.

What is its empirical formula? So you need to draw up your grid, work it out, and come up with the formula for potassium phosphate.

Pause the video and come back when you're ready.

So here's the answer.

So remember the charge value for a potassium ion is one, and there were three.

The charge on the phosphate ion is three.

Then the phosphate ion has the highest charge value, so we allocate that one in the ratio block.

We would multiply the ratio by charge value to give us three.

We know that the potassium ions must balance the phosphate, so we put three of the total charge for the potassium ions.

We divide the total charges by the charge value.

Three divided by one gives us a ratio of three, the potassium ions.

So there are three potassium ions for every phosphate, K3PO4.

Well done if you've got that correct.

Let's have a go at Task A.

So we've got a series of sentences here, and what I'd like you to do is use a word from the box to complete the sentences.

So pause the video and come back when you've completed the sentences.

How did you do? Let's have a look at the answers then.

So "Salts have a variety of uses, including flavouring food, plaster casts and fertilisers.

Salts are compounds composed of many positive and negative ions.

These are held together by strong electrostatic forces of attraction, i.

e.

ionic bonds, forming a giant 3D crystal lattice.

The chemical formula of a salt is the same as its empirical formula, the simplest whole number ratio of ions in the salt." Well done if you've got all of those correct.

Let's have a look at question two now.

We've got some giant ionic lattices to have a look at here, and I want you to have a look and see if you can work out the chemical formula for each of the salts shown.

Pause the video and come back when you're ready.

Welcome back.

Let's have a look.

So the first one, rubidium chloride.

We can see that the charges are balanced and for every rubidium ion there is a chloride ion.

So the ratio is 1:1, so the formula is RbCl.

b is a little bit more complicated.

Sodium is a 1+ ion and sulphate is a 2- ion and they need to balance.

And so we need two sodium ions for every one sulphate ion, so the formula is Na2SO4.

Amazing if you got those correct.

Well done.

Let's look at question three.

So I want you to determine the formula for the salt composed of potassium ions and iodide ions.

Iron III ions, remember the three in Roman numerals there means it's an Fe 3+ ion, and chloride ions.

Ammonium ions and phosphate ions.

Pause the video and join us when you've completed that.

Welcome back.

Let's have a look at the answers.

So the potassium ions and the iodide ions, the charges are the same for each iron.

The ratio's 1:1, so the formula is KI, two capitals remember.

The iron III and chloride ions, you might like to use the ratio grid again.

And basically we know that we need three chloride ions for every iron ion.

Tricky one to say that.

So the formula is FeCl3.

Well done.

And finally, ammonium phosphate.

We know we need three ammonium ions for every phosphate ion to balance them out.

And remember, we need to use brackets here to show there are three ammonium ions for every one phosphate ion.

Absolutely cracked it if you've got all of those correct.

Well done.

Let's move on to the second part of our lesson now, forming salts.

So salts are produced when an acid reacts with a metal.

Here's an example.

Hydrochloric acid plus magnesium combine together to form magnesium chloride and hydrogen.

Salts are also produced when an acid reacts with a base, which is a metal compound that will react with an acid.

These are often oxides.

So here we've got hydrochloric acid plus magnesium oxide, which form magnesium chloride and water.

And salts are also produced when an acid reacts with an alkali, which is a soluble base.

Hydrochloric acid and magnesium hydroxide combine to form magnesium chloride and water.

And just to make sure that you know where the salts are, I've highlighted them here.

Acids that we tend to use in the laboratory include hydrochloric acid, the formula HCl there, sulfuric acid, H2SO4, nitric acid, HNO3.

And you might also use ethanoic acid, which has the formula CH3COOH.

Vinegar contains ethanoic acid.

In solution, acids release hydrogen ions, H+.

And if we look at all the acids there, we can see that they've all got hydrogen in their formula.

So let's have a look at some common bases now that you might use in the laboratory.

So sodium hydroxide, NaOH.

And just remember that soluble bases are also called alkalis.

Copper II oxide.

And in water, these bases will release or produce hydroxide ions, OH-.

And there we are.

We can see all the hydroxides.

So sodium hydroxide, copper hydroxide, ammonium hydroxide.

Let's have a look at what happens when we mix acids and bases together now.

So the reaction between an acid and a base produces a salt and a by-product, and we call these neutralisation reactions.

And there's a general reaction equation that we can use here.

Acid plus base combines together to produce a salt and water.

So let's look at a specific example here.

Hydrochloric acid combines with sodium hydroxide to form sodium chloride and water.

So we've got the acid, the base, the salt, and the water.

During a neutralisation reaction, hydrogen ions from the acid react with the base's hydroxide ions.

And the reaction between these ions forms water.

Pure water is neutral.

It has a pH of seven.

Remember there is nothing else in pure water, it is simply H2O.

A neutralisation reaction can be represented by the ions that react to form the neutral substance.

So we've got the hydrogen ions from the acid, the hydroxide ions from the base forming the neutral product water.

And look at the state symbols there.

Water is a liquid.

Let's have a quick check.

Which reaction equation below describes a neutralisation reaction? Well done if you've got b, and even better if you've got d as well and noticed that was correct, fantastic.

You might be wondering why a was incorrect.

Look at the state symbols.

The hydrogen ions are not liquid, they are aqueous, so that is not correct.

And c is not correct because water, H2O, is liquid.

It is pure liquid, nothing else.

It's not dissolved in anything else.

The other ions in a neutralisation reaction combine to form the salt.

So hydrochloric acid plus sodium hydroxide gives sodium chloride, which is the salt, and water.

So first of all, let's get rid of the hydrogen ions, and the hydroxide ions, and the water 'cause we know what happens with those, and let's look at the other ions involved.

So we've got chloride ions and we've got sodium ions.

The chloride ions from the hydrochloric acid separate from the hydrogen ions and recombine with the sodium ions from sodium hydroxide to form sodium chloride, a new product.

Let's look at how we name salts.

And so the first part of the salt's name comes from the metal ion, which in this case is coming from the base, sodium hydroxide.

And the second part of the salt's name depends on the acid that's being used.

So we were using hydrochloric acid here, and so the salt ending would be chloride, and that's where the sodium chloride comes from.

Let's have a quick check.

So which salt would be produced when nitric acid reacts with potassium carbonate? Well done if you said potassium nitrate.

Remember the first part of the salt's name comes from the metal ion, potassium, and the second part comes from the acid that's been used, so the nitrate comes from the nitric acid.

Fantastic, well done.

Cracking this.

Let's go on to Task B now.

So I want you to match each keyword to the most appropriate description.

Pause the video and come back when you've completed the task.

Welcome back.

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

Hydrogen ion is the H+, which is released by an acid.

Salt is the name dependent on the acid that's used to form it.

Hydroxide ion is OH-, which is released or produced by a base.

A base reacts with an acid to form a salt.

Neutralisation is a reaction that forms a neutral product, which would be pH seven.

And acid reacts with a base or a metal to form a salt.

Well done if you've got those correct.

Let's look at question two.

I'd like you to classify all these substances as either an acid, a base, or a salt.

Pause the video and come back when you've had a go.

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

Okay, so we've got ethanoic acid, sulfuric acid, hydrochloric acid, and nitric acid there.

We've got sodium hydroxide, copper II oxide, potassium hydroxide, and magnesium oxide as bases.

And then the others are all salts.

Amazing job if you've got those correct.

Let's have a look at question three.

So complete the following neutralisation reaction equations.

So see how you do.

And don't forget in d, we're looking for a state symbol as well.

Pause the video and come back when you're ready.

Welcome back.

Let's have a look.

So here's the answers.

Well done.

I've got a question four for you as well.

So a barium meal allows X-ray imaging of some of the soft tissues, including the stomach.

Barium sulphate is a salt that's used to create a barium meal.

Suggest a suitable acid and base to produce the salt barium sulphate.

Pause the video, come back when you're ready.

Okay, let's have a look.

So the only acid that we could really use to produce the metal sulphate here is sulfuric acid, and then the base could either be barium oxide or it could have been barium hydroxide.

Well done.

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

So let's have a look at our summary.

So salts are giant 3D ionic structures that form crystals with a regular arrangement of ions.

We looked at potassium chloride and we also looked at magnesium sulphate.

And you may well have seen sodium chloride models in your laboratory.

The empirical chemical formula of a salt provides the ratio of metal to non-metal ions it contains.

And a salt is formed when an acid neutralises a base.

And the general equation that we use is acid plus base combine to form salt plus water.

Acids release aqueous hydrogen ions and bases release or produce aqueous hydroxide ions.

And during a neutralisation reaction, hydrogen ions and hydroxide ions combine to form pure water, H2O.

Well done.

I hope you feel more confident now about being able to describe salts, how to name them, reactions that form salts, and also to work out their empirical formulae.

Well done, and I look forward to working with you again next time.