Lesson video

Welcome to today's lesson.

We're going to be looking at multistep procedures today, or methods, and we're going to see how they can best be adapted.

This lesson is part of the unit, "Making salts." So let's get started.

And here's today's lesson outcome.

So by the end of it, you should feel much more confident in being able to describe and also explain adaptations to a multistage chemical procedure.

And we might do this to alter or improve the quality or the yield of the product.

And here are today's keywords.

So a method describes how an experiment is carried out.

It's a step-by-step procedure.

Apparatus is a piece of equipment that is designed for a particular use.

When we talk about evaluating something, we're talking about making a judgement about it with respect to a particular purpose.

And adapting means that we're making it suitable for the use or the purpose.

So for example, the equipment, we might change that, or we might change the steps in an experimental procedure.

So first of all, we're going to look at making salts and then we're going to look at adapting procedures to make salts.

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

Salts are very useful compounds.

They're ionic compounds.

And you'll remember sodium chloride is an ionic compound.

We have different chemical reactions to make salts.

So one such reaction that we can actually carry out is that between an acid and a base.

And we call that a neutralisation reaction.

Let's just think about bases for a moment.

There are three different types of bases.

Hydroxides, which contain hydroxide ions, like sodium hydroxide and magnesium hydroxide.

We have oxides that contain the oxide ion, for example, potassium oxide and copper oxide.

And we have carbonates, which contain the carbonate ion for example, calcium carbonate and zinc carbonate.

And there's one further type of base, ammonia, which produces hydroxide ions when it's dissolved in water.

And here's the chemical equation.

So ammonium plus water makes ammonium ions plus hydroxide ions.

Let's have a quick check.

Which of these are bases? What did you think? Well done if you said A, that's potassium hydroxide, B, magnesium oxide, and also ammonia, NH3.

Now C is copper sulphate, and that is a salt, but it's not a base.

Well done if you've got all three correct.

Hydroxides and oxides react with acids.

And here's the general equation.

So if you've got a hydroxide and we combine it with acid it will produce a salt and water.

So let's look at some specific examples first of all.

So sodium hydroxide and nitric acid produce sodium nitrate and water.

And sodium nitrate, remember, is the salt there in that equation.

Now let's look at oxides now.

So an oxide and an acid also produces salt and water.

Copper oxide and sulfuric acid will make the salt, copper sulphate, and water.

So we've looked at hydroxide and oxide there.

So let's look at carbonates now.

Carbonates react with acid to produce three products now.

A salt, water and carbon dioxide.

And there we've got the general equation for any carbonate.

Let's look at some specific examples.

So here we've got calcium carbonate and hydrochloric acid and they combine together to produce calcium chloride and water and carbon dioxide.

And we can see the bubbles there, the effervescence and those bubbles are carbon dioxide.

I wonder if you can remember what the test for carbon dioxide is? Good.

Colourless lime water will turn milky, cloudy, if carbon dioxide is bubbled through it.

Let's have a quick check.

Carbon dioxide gas is produced when a hydroxide base reacts with an acid.

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

Now, can you justify your answer? Which of those statements would help you justify why the statement is false? Well done if you said B.

Carbon dioxide gas is produced when a carbonate base reacts with an acid.

If you remember, when a hydroxide base reacts with an acid, we made a salt and water.

The methods that we use to produce a salt from an acid base reaction involves multiple steps.

The steps depend upon whether the base that we use is soluble, and we can call that, we might call that an alkaline, or insoluble.

And here we've got common soluble base that we use a lot, sodium hydroxide.

And you can see there it's in solution.

And here's a common insoluble base, insoluble calcium carbonate.

There are two main methods to producing a salt when we react a soluble base with an acid, The first step is that we neutralise the acid with a soluble base.

So we have a beaker of acid and we add the base to the acid and then we would check the pH of the solution that we produce.

And we're using pH paper, universal indicator.

And there you can see the pH paper has turned a sort of greeny colour.

That means it's neutral.

Then we need to crystallise the salt product.

So remember, what you do then is that you take the salt solution, place it in an evaporating dish, put it on top of a beaker of water that acts as a water bath and we heat it gently.

The reason we don't heat directly using a Bunsen burner is that the salt solution might spit and the evaporating basin might also shatter.

And just before we've evaporated all the water, we would remove the evaporating dish from the heat and we would start to leave it to dry so that the rest of the water can fully evaporate and the salt crystallises.

So let's have a quick check.

Which of the following pH papers indicates the salt solution is neutralised? Which of those three? Well done if you said B.

Now there are three method steps to producing a salt when we react an insoluble base with an acid.

So the first step is to neutralise the acid with the base.

Then we need to filter to remove the excess insoluble base from the reaction mixture.

And then we need to crystallise the salt product.

Obviously, step three is the same, whether we're using a soluble or an insoluble base.

So let's have a look at these in a little bit more detail.

So step one, neutralising the acid with the insoluble base.

It actually helps if we gently heat the mixture and we keep adding the base until it's in excess, in other words we can still see it.

So step one, neutralising the acid with the base, the insoluble base.

It actually helps if we can gently heat the reaction mixture.

We keep adding the insoluble base until it's in excess.

In other words, we can still see it at the bottom of the beaker there.

We're stirring all the time.

And then we would use pH paper to confirm that the salt solution is actually neutral.

Step two, we then need to filter.

So we pour the reaction mixture into the filter funnel and filter paper there to remove the excess base.

And then we get rid of the excess base.

We dispose of it safely.

The salt solution is then kept for the last step of crystallisation.

And remember, that's exactly the same as for a soluble base.

Let's do a quick check.

Which of the following equipment would be used to crystallise the salt solution? Well done if you said C.

A is simply filtering off the excess base.

That wouldn't create the crystallisation process.

B, that's the beginning of the process, when we're heating the base and the acid gently.

So it has to be C.

Let's have a look at task A now.

Complete the following word and symbol equations for the reaction of different bases with acids.

So we've got magnesium hydroxide and nitric acid.

And then you've got to complete the word equation to say what the products would be.

And then in part B, you've got that reaction and we're looking for the symbol equations now.

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

Okay, let's have a look and see how you did.

So for the word equation then, magnesium hydroxide, nitric acid would make the salt, magnesium nitrate and water.

And here's the symbol equation.

Don't forget the state symbols.

Sodium carbonate and sulfuric acid, remember, a carbonate and acid produce three products.

So sodium sulphate, water and carbon dioxide.

And here's the symbol equation.

Nickel oxide and hydrochloric acid make nickel chloride and water.

And then here's the symbol equation too.

Again, don't forget the state symbols.

Let's have a look at question two.

So select and list from the following apparatus, those which you'd need for each of the insoluble base reacting with acid method steps.

So for neutralisation, which equipment do you need? For filtration, which equipment do you need? And for crystallisation, which equipment do you need? You can use the apparatus pictured several times if you so wish.

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

Okay, let's have a look.

Now I've put mine into a table 'cause it just helps make it easier to see.

For neutralisation, we need the Bunsen burner to gently heat the reaction mixture.

And if we're using a Bunsen burner, we would be using a tripod and a gauze and a mat actually as well.

We need a beaker, for the heating the mixture.

We need a measuring cylinder to work out how much acid we need.

And we need a spatula for the base.

Let's have a look at filtration now.

So we need the conical flask, filter funnel, filter paper and you could put the reaction mixture in the beaker if you wanted to.

And then for crystallisation, we need a Bunsen, tripod, gauze, beaker and evaporating dish.

Well done if you've got all those correct.

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

We're gonna be looking at how we actually adapt procedures to make sure that we get a better quality of salt and perhaps a higher yield.

When we're doing the multistep methods, the whole aim is to get a high yield of pure salt.

And remember, pure salt will only contain particles of the salt and it, and because it's pure, that means it will have an exact melting and boiling points.

So you can use the apparatus there to check.

And a high yield means you get as much pure salt as possible.

There we've got some nice crystals of copper sulphate there.

So let's have a question now.

So which method of producing copper sulphate would be the best based upon both the yield and the purity? Which do you think? Okay, let's have a look.

So A, the yield is quite low there, 33% is quite low, but it's got a melting point of exactly 110.

So you know, it's always good to have the exact melting or boiling point.

Part B, that's a nice high yield, but the melting point is over quite a large range.

So that would let through quite a few impurities or contaminants.

C, 62% of a yield, so fairly good yield and we've got a melting point of exactly 110, so that's good.

D, 74% yield, okay, but again, we've got that quite big range of melting point.

So actually, so it's between A and C and obviously it's going to be C.

So, well done if you've got that correct.

In order to get a pure salt, it's necessary to avoid contamination.

And contamination is where we've got unwanted substances present in the salt.

This copper ore contains so many different substances, so it's not pure.

And what we need to do is make sure that our salts, that we're collecting, is pure.

So we have to avoid contamination by making sure that our equipment is as clean as possible.

And so we would wash that with distilled water.

Distilled water remember, is as pure as possible so it contains nothing other than H2O, and removing any of those unreactive substances from the salt.

And we would also evaluate the apparatus and the procedures that we use for each step of a method to make sure that we get the best possible method, to get the best yield and the purity of the salt produced.

So for example, in the neutralisation part of the reaction for a soluble salt, remember we were adding base to the acid and we were checking the solution was neutral using pH paper, we could make sure that we're adding the base dropwise, drop by drop by drop, when we get near to the neutralisation point.

So that would involve probably lots of testing with the pH paper, lots of different pieces of pH paper to check.

And if we went too far and the solution had become alkaline, then we need to adjust the pH back again by adding some more acid dropwise.

So which of these pH paper results would indicate that the salt solution has become too acidic? Well done, well remembered.

And here if it had become more acidic, we'd actually need to neutralise the solution by adding more soluble base.

So let's have a look at any adaptations we can make to the neutralisation part when we use an insoluble base.

So we could use a measuring cylinder to add a set volume of acid to the beaker.

That would also make the experiment repeatable.

We gently heat the acid to speed up the rate of the reaction and we're always adding an excess of the base to ensure that all the acid has reacted.

That's very important.

And we're stirring to keep agitating the reaction mixture and make sure that reaction is happening.

And then we would use the pH paper to confirm that the solution is neutral and therefore that tells us that all the acid has reacted.

Let's have a look at the adaptations to filtration when using the insoluble base.

So we decant the salt solution into the filter paper and we minimise the excess base that's transferred.

We would do it very carefully.

We would gently pour small portions of the salt solution into the filter paper to prevent clogging and blocking of the filter paper.

And also making sure that we don't overfill it because we don't want anything seeping around the outside of the filter paper because we might get base then going into our filtrate.

If we do look at the filtrate and think that we've probably got some base in there, then we can refilter.

So let's have a quick check.

So salt solution particles are larger than the holes in the filter paper.

What do you think? Well done if you said false.

And now justify your answer.

Why is that statement false? Well done if you said A.

The salt solution particles have got to be smaller than the holes in the filter paper so they can pass through.

Let's have a look at the adaptations to crystallisation now.

And remember, it doesn't matter whether we've got a soluble base or an insoluble base here.

So we use a water bath to ensure the temperature reaches approximately a hundred degrees C so that we're evaporating the water.

We would only heat until we get a saturated salt solution produced.

And we can actually see salt crystals being, forming in the evaporating dish.

We never heat to dryness because the salt formed could dangerously spit out of the evaporating dish and be lost.

And when we're trying to get as high a yield as possible, that's important, as well as being dangerous.

And you may also crack the evaporating dish.

Further adaptations that we might do when we're using either soluble or insoluble bases are that we could actually allow the saturated salt solution to dry slowly in the air or we could put it into a warm oven to dry.

Now the temperature at which the saturated salt solution dries, determines the size of the crystals.

So if you leave it in air to dry really slowly, then the crystals produced will be much bigger than if you put them in an oven to dry.

Because warmer temperatures will produce smaller crystals.

We can also use filter paper to pat the crystals dry if we need to.

Let's have a quick check.

So order these steps for the crystallisation process.

What's the order? Put numbers by them.

Which is the first one? Well done if you said heat over a water bath would be number one, then we'd form the saturated solution as some of the water evaporates, then we would dry with the air or the oven, and finally pat dry with the filter paper if we need to.

Let's have a look at task B.

So Izzy wants to make some calcium chloride salt.

Here's her method.

Could you have a read of the method, and I want you to correct any errors and also suggest how she could further improve it.

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

Okay, welcome back.

Let's have a look and see how you did.

So your improved method might have looked something like this.

So the first step, we could measure out 25 centimetre cubed of hydrochloric acid using a measuring cylinder, rather than a beaker.

Gently heating the acid in a beaker.

Now Izzy wanted to make calcium chloride salt, but in her method she talked about using copper carbonate.

So actually change that.

So we're adding spatulas of calcium carbonate powder to the acid and we need to stir it until we can see the excess at the bottom of the beaker.

It's important to stir.

And then we can filter the salt solution through filter paper to remove the excess calcium carbonate before decanting the salt solution.

Then we pour or decant the salt solution filtrate that forms into an evaporating dish.

We would heat it using a Bunsen burner to form a saturated salt solution.

And then we would allow the saturated salt solution to crystallise by air drying.

How many of those did you get? Let's have a look at question two now.

So now I want you to explain to Izzy why the changes to the method, that we've shown in bold here, are improvements.

Explain to her why they're better than what she was thinking about.

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

Okay, let's have a look how you did.

So a measuring cylinder is a more accurate way of measuring liquid volumes.

Heating the acid speeds up the rate of the reaction, needs to be gently though.

Calcium carbonate is needed to produce calcium chloride.

Stirring helps mix the reactants and helps them to react.

Filtering is the best way of separating the excess solid base and the salt solution.

The salt solution filtrate should be carefully poured into the evaporating dish so we don't have any spillages, and we get the maximum yield collected.

And then we heat the salt solution to evaporate some water to get this saturated solution, which helps the salt to start to crystallise.

And then we will put it out to air dry to allow the salt crystals to form slowly, which would mean the crystals are larger and we don't risk losing any.

Well done.

So if you've got most of those, you've been able to show how to adapt a multistep procedure.

Let's have a look at the summary from today.

So reacting a metal hydroxide with an acid can produce a salt and water.

Reacting a metal carbonate with an acid produces the desired salt, water and carbon dioxide gas.

So three products there.

And when react a metal hydroxide or a metal oxide with acid, we only get two products.

A pure sample should be prepared with the equipment washed in distilled water to avoid any contamination.

We must gently heat the acid to speed up reaction and we keep stirring and adding the base to excess to make sure that all the acid reacts.

And then the salt should be dried using an appropriate method, using air, dabbing with filter paper or in a warm oven.

Well done.

I hope you feel a lot more confident now in being able to adapt a multistep chemical procedure in order to increase the yield or the quality of the salt that we produce.

Well done.

I'll see you next time.