Lesson video

Hello, my name's Mrs. Niven and today we're going to be looking at how to make a pure sample of a soluble salt as part of our unit on making salts.

Now you may have some experience of what we talk about in today's lesson from your previous learning, but what we do in today's lesson will help us to answer those big questions of what are substances made of, but also how can substances be made and changed.

So hopefully by the end of today's lesson, you'll feel more confident being able to carry out a multi-step chemical procedure in order to form a pure dry sample of a soluble salt.

Now the key words that we'll be using throughout today's lesson are provided with their definitions on the next slide.

And you may wish to pause the video here so you can make a note of those keywords and their definitions for reference later on in the lesson or later on in your learning.

Now today's lesson is broken into two parts.

First, we'll be looking at how metal oxides react with acids.

And then, we'll move on to see how that information can be used to help us decide how to make a soluble salt.

So let's get started by looking at how metal oxides react with acids.

Now, soluble salts can be made when we react an acid with an insoluble base like a metal oxide.

And we can represent these reactions which are neutralisation reactions generically with the equation of metal oxide plus acid makes a metal salt and water.

And for example then, we might take magnesium oxide, react it with hydrochloric acid and form then magnesium chloride and water.

Now the type of salt that's actually produced or the name of the salt more accurately that's produced during these neutralisation reactions depends on the type of acid used.

So if we're using hydrochloric acid, you form a chloride.

Sulfuric makes a sulphate.

Nitric acid makes a nitrate.

So if we look at these three examples, I have zinc oxide, that is my metal oxide reacting, but I use three different acids.

And as a result of that, I make three different salts.

So it's important that we're choosing the correct acid and metal oxide combination in order to create the desired salt.

Let's stop here for a quick check.

Name the acid that reacts with iron oxide to produce the salt iron sulphate.

Well done if you chose b, sulfuric acid creates a sulphate salt.

Very well done if you got the correct, guys, great start! Let's try another one then.

What type of reaction takes place when a metal oxide reacts with an acid? Well done if you chose neutralisation.

That's exactly the right type of reaction that is taking place, well done! Now when we are going to create a soluble salt by the reaction of a metal oxide in an acid, there are three main steps.

The first step is actually neutralising that acid using the metal oxide base reacted.

Then we need to filter any excess insoluble metal oxide from that reaction mixture.

And finally, we're going to then crystallise the soluble salt product out of solution.

Let's look at each of these steps in a little bit more detail.

Now, the first step is to neutralise the acid to make sure all of it has reacted, and we're going to do that by adding small spatula portions of the powdered metal oxide to a set volume of acid, and we're going to stir each time.

That helps the copper oxide then to mix in with the acid, but also for those acid particles to collide with and react with those metal oxide particles.

The next thing we're going to do is we're gonna gently heat this mixture now.

And what that does then is it increases the rate of reaction.

If we were to leave it to sit at room temperature, it could take quite a long time.

By heating it gently, we're just providing a little bit more energy that helps this reaction to happen in a more reasonable timeframe.

We're gonna continue adding some metal oxide then until we start to see some of that solid metal oxide collect at the bottom of the beaker.

Now that indicates then that the acid has reacted because an excess is added.

We can see the extra, excess, metal oxide collecting at the bottom of that beaker, but that's not enough.

We need to double check that that reaction mixture is actually neutralised and we're going to check that using indicator paper, pH paper, and then comparing the colour that forms to our reference sheet that comes with that particular paper that's being used.

Let's stop for another quick check.

True or false? When reacting a metal oxide and an acid, a colour change indicates that the acid has been neutralised.

Well done if you chose false, but which of these statements best justifies that answer? Well done if you chose a, neutralisation is reached when an excess of unreacted metal oxide appears in the reaction mixture, and we can double check that using pH or indicator paper and then cross-referencing the colour change on the paper to our reference sheet.

So well done if you managed to get that correct, good job! So once we have successfully neutralised the acid by reacting it with our metal oxide base, we need to remove that excess metal oxide and we'll do that using filtration.

So you'll need a funnel, filter paper, and a conical flask in order to do that.

So by filtering out the reaction mixture, we remove that excess reactant, the metal oxide, something we've used too much of.

Now that excess reactant of the metal oxide, if you remember, was a solid.

And therefore, it will collect as residue in the filter paper.

That needs to be disposed of safely.

And then, you need to keep the filtrate or the soluble solution for the next step.

Another quick check then.

Which of the diagrams below correctly shows what should be kept for the next part of our experiment after filtration? Well done if you chose c.

This diagram has circled the filtrate, which is our soluble salt solution, whereas the other two have circled the metal oxide excess that has been removed from our solution that we no longer need.

So well done if you managed to get that correct, good job! So now that we have successfully created our soluble salt solution by neutralising the acid with an appropriate metal oxide and filtering out the excess metal oxide that reacted, we need to remove that salt from solution and we do that by crystallisation.

So in order to do that, we need to heat the solution in an evaporation dish over a water bath to form a saturated solution.

And it's really important that we're doing this gently and carefully.

We don't want to heat the crystals to dryness as they'll spit out of the dish.

It's one of the reasons why we're heating our solution in an evaporation dish over a beaker of boiling water or a water bath rather than directly on the heat.

We'll then leave the solution to dry, to evaporate to dryness.

And if necessary, we could even dry the crystals by gently dabbing at them with some filter paper or leaving them in a warm oven.

Another quick check, what is the process used to obtain copper sulphate crystals from a copper sulphate solution? Well done if you chose evaporation.

Crystallisation would also work, but that is not one of our options.

So very well done if you manage to choose the correct method.

Great job, guys! Now during crystallisation, essentially what's happening is that water is evaporating from our soluble salt solution and escaping into the environment.

And what that does is leave behind a saturated solution.

Now, a saturated solution, by definition, is a solution in which no more soluble salt can dissolve at a given temperature.

Now, solubility decreases as the temperature goes down.

So that means that as a solution cools, it can't dissolve as much of the solute.

And as a result, as a solution cools, then the salts begin to crystallise.

They fall out of solution essentially, forming these lovely crystals.

If we want then a dry salt sample of these crystals, we can either leave those crystals to dry in the air or put them into an oven that would then dry that solution further.

Okay, one last quick check.

True or false? Dry salt crystals can be obtained by using a bunsen burner to evaporate the salt solution to dryness.

Well done if you said false, but which of these statements best justifies that answer? Well done if you chose a, the dry salt crystals can be obtained by either drying them in the air or putting them into an oven.

Very well done if you managed to get those correct.

Good job, guys! Time for the first task in today's lesson.

I'd like you to please match the following pieces of equipment to their uses in the method for producing a soluble salt.

So pause the video here and come back when you're ready to check your answers.

Okay, let's see how you got on.

So the measuring cylinder will be used to measure a set volume of acid while the spatula is used to add portions of the metal oxide and possibly stir that reaction mixture.

The filter funnel and paper are used to separate the soluble salt and the excess insoluble metal oxide from each other.

And the evaporation dish is used to allow water to evaporate and produce a saturated salt solution, which means the bunsen is used to initially heat the acid and speed up the reaction, but it can also be used later on in the procedure to evaporate some of the water producing that saturated salt solution needed to create the crystals.

So very well done if you managed to match those all correctly.

Great job, guys! For the second part of this task, I'd like you to complete both the word and symbol equations for the reactions of these metal oxides reacted with various acids.

So pause the video here and come back when you're ready to check your work.

Okay, let's see how you got on.

So for a, magnesium oxide reacts with nitric acid to form magnesium nitrate and water.

So if I change these chemical names into formula, I should have formed them MgNO3 2 + H2O.

For b, sodium oxide and sulfuric acid will form sodium sulphate and water, which forms the formulas of Na2SO4 + H2O.

And for c, nickel oxide and hydrochloric acid will form nickel chloride and water, which have the formula of NiCl2 + H2O.

Now the main thing here is you were asked to do two different things.

At the very least, we should be able to write the word equations for these reactions, but very well done if you also managed to write the symbol equations for these reactions.

And incredibly well done if you've remembered to include those state symbols.

Very, very well done! Really impressed, guys, keep it up! So now that we're feeling more comfortable discussing how metal oxides will react with an acid, let's look at how we can take that information to make a specific soluble salt.

Copper oxide can be reacted with sulfuric acid to make a soluble salt of copper sulphate.

What I'd like you to do is we're going to watch a video outlining how to create this soluble salt from copper oxide and sulfuric acid in a laboratory.

And whilst we watch this video, I'd like you to make notes about each step.

So to create our soluble salt from our sulfuric acid and copper oxide, I'm going to pour 25 centimetres cubed of our sulfuric acid into a 100 centimetre cubed beaker and place this on top of a tripod and gauze.

I then turn the bunsen burner to a gentle blue flame, place it underneath the beaker, and very gently start to warm up that sulfuric acid.

Now you'll notice that there's no bubbling involved.

We're simply trying to create those particles to move around a little bit more so that the reaction happens a little bit more efficiently.

Once we then remove that bunsen burner because the sulfuric acid has been warmed gently enough, we're going to slowly add small amounts of the copper oxide and you can see that it's reacting because we start to get this bluish tinge to the solution.

There's a little bit of bubbling involved and we're just gonna gently do that slowly and steady.

And then, we're going to stir that mixture with a stirring rod to allow those copper oxide particles to collide with the sulfuric acid particles.

And then, we're gonna test the solution's pH on universal indicator paper.

We can see that it's a bright red, indicating that there is still some sulfuric acid that's unreacted.

So we add a little bit more copper oxide to make sure that that sulfuric acid has fully reacted.

Now, every time we add a little bit more, we're going to be stirring that mixture and then testing the pH of that reaction mixture on the universal indicator paper.

And what we're looking for then is for the colour to match that on our reference pH to show that it has fully reacted.

So we're looking for that neutral colour.

I haven't quite reached there, so we're just putting a little bit more in of our copper oxide, mixing that solution together again.

Testing it one final time just to see, and we have now reached the colour that matches our reference guide to show that it's neutralised.

So I'm now going to need to remove the unreacted copper oxide.

And to do that, we're going to filter the solution.

Now, if you let your reaction mixture just stand for a little bit, you will see that the unreacted copper oxide falls to the bottom of your beaker and you can decant then then your copper sulphate solution into your filtration set up.

Now this is gonna take a little bit of time.

Patience is a virtue here.

You need to do nice and steady so none of the solution overflows your filter paper and contaminates your filtrate.

So do take it nice and slow here.

You don't want to have to start all over again.

But you can see that the unreacted copper oxide stays in that beaker or is collected as the residue in our filtration setup.

And then we're left with this beautiful blue colour of our filtrate, which is our solution of our soluble copper sulphate salt dissolved in water.

Now the next thing I need to do is I need to get that salt out from solution, so I'm going to heat it gently.

But to do that, I'm gonna have a beaker, quite a large beaker with water in it.

And I've just added some anti-bumping granules.

And what that does is creates small bubbles in the water whilst it's boiling.

Now, then I put my evaporation dish on top of the beaker and pour my filtrate from the previous action into the evaporation dish.

Change the bunsen burner to a gentle blue flame, place it underneath the beaker, which is now on the tripod and gauze and warm that gently.

Now from the top, this is what it should look like.

Once that water is boiling, you can see that it's very gently then going to heat my solution rather than heating it directly.

This is a far safer way of doing it.

And then once you are finished, you can either continue heating it until it reaches this stage, or once you have those crystals just forming on the outside, you can remove the heat and place your solution on the side to cool and crystallise.

And sometimes, that will form slightly larger crystals, but then you have then created your dry soluble salt.

Okay, time for the next task in today's lesson.

What I'd like you to do is to use the information from the video you've just watched to write a method for the reaction of copper oxide with sulfuric acid.

And I'm gonna recommend that you use labelled diagrams and don't forget what makes a good method.

We're talking about short, sharp, clear instructions that include volumes, masses, equipment, things like that.

So we're looking for a good method that you could pass to somebody else that would be able to be followed to create a copper sulphate salt.

Once you've done that and you've checked your work for it, we're going to move on to carry out the actual practical to make copper sulphate crystals from copper oxide and sulfuric acid.

From this, I'd like you to then write both the word and symbol equations for this reaction, including the state symbols.

I'd also then ask you to explain how to check that the reaction is complete and why copper sulphate solution is obtained by filtration.

And finally, I'd like you to suggest a different method that may be used to obtain dry copper sulphate crystals.

So pause the video here while you complete the task, and then come back when you're ready to check your answers.

Okay, to write your method then for the reaction of copper oxide and sulfuric acid, the first thing you need to do is to add some portions of copper oxide to a set volume of warmed sulfuric acid, and we're going to stir that.

So if you specified the volume, very well done, 25 centimetres cubed tends to be what's used.

You're going to then continue adding copper oxide until some solid can be found and seen, sorry, at the bottom of the beaker indicating that the acid has reacted.

And we're going to double check that it is fully reacted by testing the reaction mixture with some universal indicator or pH paper to confirm that that solution is now neutral.

Next, we're going to filter that reaction mixture to make sure that the excess copper oxide has been removed.

And then, we're going to keep the filtrate, which is the blue copper sulphate salt solution.

Now remember, we were asked for some labelled diagrams here, so ensure that we have an equipment list with our method.

So we've got this example, the conical flask, the filter paper, the funnel that is required as well.

Next, we're going to heat that solution in an evaporation dish over a water bath in order to form that saturated solution.

So the equipment we need will be heat proof mat, bunsen burner, tripod, gauze, evaporation dish, and that water bath.

You'll then going to leave the solution to evaporate to dryness.

And if necessary, dry those crystals gently by dabbing with filter paper or leaving in a warm oven.

Next, you were asked to carry out the practical by following that method to form copper sulphate crystals from the reaction of copper oxide and sulfuric acid.

And your crystals may look a little bit like this.

Now the larger crystals form by leaving your solution to cool slowly over time in order for those crystals to grow.

You'll have smaller crystals if they are warmed a little bit more quickly and those crystals form a lot faster and they don't have enough time to grow.

So that's why you might have different sized crystals that have formed as a result of this.

But very well done if you managed to get these beautiful blue crystals forming.

You were then asked to write the word and symbol equations for this reaction.

So it's copper oxide plus sulfuric acid makes copper sulphate and water, and writing the symbol equation for this reaction, including state symbols, should say CuO solid + H2SO4 aqueous makes CuSO4 aqueous + H2O as a liquid.

Very well done if you managed to get those correct, guys, fantastic work! You were then asked to explain how we might check to ensure that the reaction is complete.

Now you can confirm that all of that acid has reacted by one, observing that excess solid copper oxide in that reaction mixture.

But more importantly, by checking it has neutralised by using that pH or indicator paper and comparing the colours to your reference guide for that indicator paper.

You were then also asked to explain why copper sulphate solution can be obtained using filtration as one of the methods.

And it's because copper sulphate is soluble and will be in that solution, the filtrate that's collected as a result of filtration because the copper oxide that's excess in our reaction mixture is insoluble, it remains in the filter paper as the residue.

And finally, you were asked to give different methods of obtaining the dry copper sulphate crystals.

So that's the dry copper sulphate crystals.

So once we've initially heated to obtain that copper sulphate solution that's been saturated, we could follow that up by simply evaporating that water by leaving it in the air, maybe on a window sill somewhere, or putting it into the oven to dry.

So very well done if you recommended some other methods of obtaining those dry copper sulphate crystals, guys.

I hope you had a good time doing this practical.

It's one of my favourites.

Brilliant work if you've managed to do that.

Wow, this has been a full on lesson.

So let's just go through what we've managed to learn today.

Well, we've learned that reacting a metal oxide with an appropriate acid can form a desired salt and water.

And that if we add metal oxide to excess, we ensure that all of the acid fully reacts to form that salt and water, and that forms then a neutral reaction mixture.

The excess copper oxide then can be removed from that mixture using filtration so that the filtrate contains that soluble salt and water only.

And then, we can remove that water from the filtrate by evaporation, and that then will leave behind the salt that we wanted from that reaction.

I had a great time learning with you today.

I hope you had a good time learning with me and I hope to see you again soon.

Bye for now.