Lesson video

Hello and welcome to today's lesson.

My name's Mrs. Clegg.

We're gonna look at ionic equations for the formation of salts today and we'll also be thinking about oxidation, reduction and spectator ions too.

This lesson is part of the "Making Salts" unit, so let's get going.

Here's today's learning outcome.

So by the end of it, you should feel a lot more confident and comfortable writing balanced ionic equations for the formation of salts, including the ionic equation for the formation of water and using state symbols.

Here's today's keywords.

You might like to pause the video now and make some notes on these definitions to help you during the lesson.

Today's lesson is split into two parts, representing reactions and ionic equations for salt formation.

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

Chemical equations are like the recipes of chemistry.

They tell us what's needed and they tell us what will be made.

Different types of chemical equations can be used to present different information.

So we can use word equations for example, to represent reactions and it tells us the name of the reactants and the name of the products.

So that's a word equation and it's useful for those who are new to chemistry and who use the same language, but it's not universally understood, because not everybody is able to understand English.

And it doesn't give as much information actually about the atoms involved or the ratios involved.

There are no values in a word equation.

So another way is to use symbol equations.

And again, they tell us the reactants and the products and they use chemical formulae.

And the downside to this is that you need to be able to interpret chemical formulae and the state symbols.

It does tell us the elements that are present and it does tell us the ratio of atoms in each substance.

And when a symbol equation is balanced, the coefficients, the big numbers at the front, tell us the ratio of each substance in the reaction.

Let's have a quick check.

So true or false? Coefficients are found in both word and symbol equations.

Is that true or is that false? Well done if you said false and can you explain your answer now? Can you perhaps write two sentences? So let's have a look.

So the coefficients, the big numbers, are only found in symbol equations and they balance the number of atoms of each element in the reactants and products.

Great if you've got that.

Let's move on.

So some chemical equations provide hints to the type of reaction that's taken place.

So in this reaction, we can see that one reactant has produced multiple products, and that is a decomposition reaction.

Precipitation reactions are indicated by the aqueous reactants and at least one solid product.

So we've got a solution of potassium iodide and lead nitrate reacting together and forming lead iodide, which is a solid, and potassium nitrate solution.

Ionic equations represent the reaction between the ions in a solution and these chemical equations include only the chemical species that actively participate in the reaction.

They exclude what we call spectator ions, those which do not participate directly in the reaction, they stay dissolved in the solution.

So let's have a look at this equation again.

So potassium iodide and lead nitrate, both aqueous solutions, combine together to form lead iodide precipitate and potassium nitrate solution.

So if we look for the spectator ions here, those which do not participate directly in the reaction and remain dissolved in the solution, we would see that it's going to be the potassium ions and the nitrate ions.

We should also remember that electrons can be transferred or shared, forming bonds between atoms and half equations indicate which atom has lost or gained electrons.

So this is a different way again of showing what's happened in a reaction.

So if we think about the formation of sodium chloride from sodium and chlorine reacting together, the sodium metal undergoes oxidation.

And if you remember the mnemonic, oxidation is loss, we know that this means it's lost electrons.

So we can represent this in a half equation.

So just let's look at sodium first of all.

So the sodium reacts and an electron will be transferred.

So we form a sodium ion and an electron.

And then if we look at the half equation for chlorine, it undergoes reduction, that means it gains electrons.

So here's the half equation and there's the electrons that are being gained.

Now, an easy way to remember this in terms of oxidation and reduction and what happens to electrons is OIL RIG.

You might have come across that before.

So oxidation is loss of electrons and reduction is a gain of electrons, OIL RIG.

Let's do a quick check.

So a spectator ion is usually oxidised or reduced during the reaction.

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

Can you explain your answer? Let's have a look at the answer.

So spectator ions do not directly take part in a chemical reaction.

They remain dissolved in solution and are found in both the reactants and the products.

Well done if you got that correct.

Let's have a look at task A.

So what I'd like you to do, is match the terms to their description.

Use one line per key term.

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

Okay, let's have a look.

So ionic equation represents reactions between ions in the solution.

A half equation has electrons.

Spectator ions do not participate in the reaction.

State symbols indicates the physical state of a substance, solid, liquid or gas.

A word equation represents reactions using chemical names and a symbol equation uses formulae to represent the reaction.

Amazing if you've got all those right, well done.

Let's have a look at question two.

So I want you to write the particles that are represented by this equation or the state represented by the state symbol in each box.

So if the box is pointing to the state symbol, what is the state symbol? What does it mean? Write it in words.

Or if it's pointing at a chemical, are the particles atoms or ions and which particular atom or ion are they? So you can see copper chloride there.

It's pointing to the copper and that would be a copper ion and it would have a charge of two plus.

So pause the video and come back when you're ready.

Okay, let's have a look how you've done.

So let's start on the left-hand side.

So the box there is pointing to the chloride ion.

And then we've got the ion atom and we've got the iron ion and then we've got a state symbol which means aqueous and we've got the copper atom and the copper is a solid.

Well done.

So let's have a look at question two B.

So what I'd like you to do now is complete the table to show how the particles that make up the reactants, the copper chloride and the iron, compare with the product particles, the iron chloride and the copper.

So which of the reactants are atoms and which are ions? Pause the video and come back when you're ready.

Okay, let's have a look, see how you've done.

So on the reactants and the product side, which are atoms? So we've got iron in the reactant side and we've got copper in the product side.

And so therefore, in terms of ions on the reactant side, we've got copper and chloride ions.

And on the product side, we've got iron and we've got chloride ions.

Well done if you've got those correct.

Let's have a look at question three and four now.

So question three.

When copper oxide reacts with hydrochloric acid, a salt and water form.

So I want you to name the salt, write a word equation for the reaction and then complete the symbol equation, including the state symbols.

That's question three.

Question four, I want you to identify which half equation show oxidation or reduction, and then explain why you think that.

So pause the video and join us when you've completed them.

Let's have a look.

Okay, so what is the salt? When copper oxide reacts with hydrochloric acid, what's the salt that's formed? It would be copper chloride.

Write a word equation for the reaction.

It would be copper oxide plus hydrochloric acid combines to form copper chloride and water.

And then we've got the symbol equation there and the state symbols.

So how did you do? Let's go to question four now.

If you need to pause the video at any time, do so.

Question four, let's have a look at the half equations that show oxidation or reduction.

So is this oxidation or reduction? It is an oxidation reaction, because the calcium has lost two electrons.

B, oxidation or reduction? It's reduction, because each oxygen atom has gained two electrons.

Part C, oxidation or reduction? Again, reduction, because the aluminium ion has gained three electrons.

And part D, oxidation or reduction? Neither, because no electrons have been transferred, so we know therefore the chloride ion here is behaving as a spectator ion.

Amazing if you've got those right.

Well done, well done.

Let's move on to the second part of our lesson today.

Acids are substances that dissociate or ionise to release hydrogen ions when they're in solution.

So hydrochloric acid dissociates to form hydrogen ion and a chloride ion and this can be represented by a symbol equation.

Now, what about alkalis? Well, they release hydroxide ions when they react with acids to form salts.

Neutralisation occurs when equal concentration of hydroxide ions and hydrogen ions released by the acid, react to form water, and here's the ionic equation.

And it's actually called the ionic equation of neutralisation.

And so neutralisation only occurs when we've got equal concentrations of hydroxide ions and hydrogen ions.

The law of conservation of mass states that matter cannot be created or destroyed.

So just as the number of each type of atom needs to be balanced in a symbol equation, so does the charge in a ionic equation.

In this ionic equation of neutralisation, the one positive ion, the hydrogen, reacts with the one negatively charged ion, the hydroxide ion.

They cancel out each other's charge to be neutral and the product is a neutral compound which has no charge.

When a neutralisation reaction happens, the general equation is acid plus base combines to form salt and water.

Let's look at a specific example.

The equation for the neutralisation of hydrochloric acid with sodium hydroxide solution.

The word equation is this and the symbol equation is this.

And there's the state symbols.

Now, let's have a look at this and see which are the spectator ions.

Remember, to be a spectator ion, they don't take part and they remain dissolved in solution.

So the ions forming the salt, in this case, the sodium and chloride, are spectator ions.

Let's have a check.

Which of the spectator ions in the neutralisation reaction, sulfuric acid plus potassium hydroxide combine to form potassium sulphate and water? So which would you say the spectator ions are? They don't directly participate in the reaction and remain dissolved in solution.

Potassium and sulphate.

Well done.

Let's have a look at the steps now to writing an ionic equation.

We have to start by writing the full balanced chemical equation for the reaction.

And then for any compounds in aqueous solution, we need to split them into their constituent ions, the ions they are made of.

Then we identify and remove the spectator ions.

These appear unchanged on both sides of the equation.

And then the remaining ions and compounds form the net ionic equation which represent the actual chemical change.

You might want to pause the video and take notes here.

Let's have a look at a specific example.

So hydrochloric acid reacting with sodium hydroxide.

So we need the full balanced chemical equation.

So here it is.

Then we need to split the compounds that are an aqueous solution into their constituent ions.

There we go.

So hydrochloric acid becomes hydrogen ion and chloride ions.

Sodium hydroxide is sodium ions and hydroxide ions.

Sodium chloride is sodium ions and chloride ions.

And then we've got water.

Let's identify and remove the spectator ions.

Remember these appear unchanged on both sides of the equation.

So if we have a look at those, it appears to be the chloride ions and the sodium ions.

They remain unchanged on both sides of the equation.

So let's cancel them out.

And then the remaining ions and compounds form the actual net ionic equation, which represents the actual chemical change, what has actually changed.

And the ionic equation would therefore be this, hydrogen ions plus hydroxide ions combine to form water.

So let's have a look at some examples.

So if we had to write the ionic equation for the formation of the insoluble salt, lead iodide, from this equation.

So the first thing we've got to do is make sure the equation is balanced, which it is.

Then we have to split any compounds that are in aqueous solution into their constituent ions.

So potassium iodide would be potassium ions and iodide ions.

Lead nitrate would be lead ions and nitrate ions.

And then we've got lead iodide, which is a solid and potassium nitrate is aqueous, so we split that up into its constituent ions.

So we've got potassium ions and nitrate ions.

Then we need to identify the spectator ions, which appear unchanged.

So that would be the potassium ions and the nitrate ions, which leaves us with iodide and lead ions combining to form lead iodide.

So I'd like you to have a go now at writing the ionic equation for the formation of the insoluble salt, lead bromide.

So have a look at the equation and remember the steps you have to go through.

So check it's balanced and then split compounds and aqueous solution into their constituent ions, identify the spectator ions and then the remaining ions and compounds form the net ionic equation.

So let's have a look.

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

Okay, let's have a look.

How did you do? So it is balanced, so now let's separate the compounds that are in aqueous solution into their constituent ions.

So there we go.

Then identify the spectator ions and cross them out.

So that would be the sodium ions and the nitrate ions.

And then we're left with lead plus bromide ions combine to form lead bromide.

Well done if you've managed that, that's absolutely brilliant.

You can write ionic equations.

So let's have a look at task B.

So hydrochloric acid reacts with calcium hydroxide to produce a salt and water.

I'd like you to write the full balanced chemical equation for this reaction.

Rewrite the equation showing all the ions.

Cross out the spectator ions.

Write the ionic equation for this reaction.

And what does the ionic equation tell us about this type of reaction? So have a go at that.

And then question two, write the symbol and ionic equations for the formation of these insoluble salts.

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

Let's have a look.

So question one, the full balanced chemical equation is this.

Did you get that right? Well done if you did.

And then rewrite the equation showing all the ions.

So we've disassociated hydrochloric acid into the hydrogen ions and the chloride ions, calcium hydroxide into calcium ions and hydroxide ions, calcium chloride into calcium ions and chloride ions and water.

Then cross out the spectator ions.

So they would be the chloride and the calcium.

And so we were left with hydrogen ions plus hydroxide ions produce H2O, water.

And what does this ionic equation tell us about this type of reaction? Well, it's a neutralisation reaction.

Let's have a look at question two.

So you had to write the symbol and ionic equation for the following insoluble salts.

So I always find it easier to write the word equation first and then convert that into the chemical symbol equation.

And then look at the ions that are present.

So silver ions and chloride ions combine to produce silver chloride.

And then part B, there's the answer.

So have a look, check yours and see how well you did.

Absolutely fantastic if you got all those correct.

This is not easy, so well done.

We've come to the end of the lesson now, so let's have a look at the summary.

So a chemical equation is used to represent the chemical reaction that occurs during the formation of a compound.

Ionic equations can be used to show only the chemical species that are changing within a reaction.

We always state the symbols, solid, liquid or gas or aqueous in ionic equations, 'cause that helps us to see which substances are changing.

And then the ionic equation for water formation or a neutralisation reaction is hydrogen ions plus hydroxide ions combine to form water.

Absolutely amazing, well done for sticking with it.

That was not easy.

Well done.

I look forward to working with you again next time.