Hello, my name is Mrs. Collins, and I'm here today to help you through your learning.

This lesson forms part of the unit making salts, and is called "Titrations: Making soluble salts." During today's lesson, you will learn how to accurately perform a titration, understanding the apparatus, and selecting suitable indicator to identify the end point.

Here are the key words for today's lesson.

Titration, volume, end point, strong acid, and meniscus.

Pause the video here, read through those descriptions, and make any notes you feel you need to.

Today's lesson is divided into two parts, an introduction to titrations and performing a titration.

So let's start with that introduction to titrations.

So, a titration is a method, and it's a method used to completely neutralise a strong acid with a soluble base or an alkali.

Both the alkali and the strong acid are completely ionised in aqueous solution.

So if you remember back, when an acid is ionised, the hydrogen ions dissociate, and when an alkali is ionised, the hydroxide ions dissociate.

And this reaction results in the formation of water and a soluble salt.

Here's a question based on that learning.

Titration is used to completely neutralise an acid with an insoluble base.

Is this true or false? Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answer to that question is false, and that's because an acid is neutralised by a soluble base, and that's what an alkali is, a soluble base.

So well done if you've got that correct.

Here's a followup question.

What are the products of a titration between a strong acid and a strong base? Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answer is water and a soluble salt.

So well done if you've got that correct.

Each piece of apparatus in a titration has got a specific and essential function.

So we use very specific equipment when we carry out a titration.

So the first piece of equipment you need to know about is called a burette.

And this measures and delivers the acid or the base, drop by drop into the solution, which is in the conical flask.

A volumetric pipette accurately measures a fixed volume of solution to be titrated.

So we use this to measure out the solution to put into the conical flask.

You might not have access to this type of pipette, and you might use a measuring cylinder instead, but a measuring cylinder is less precise than a volumetric pipette.

So it depends which piece of equipment you use.

A pipette filler safely draws the solution into the pipette.

So you can see in that image there we've got a volumetric pipette, and then the pink pipette filler at the top.

The conical flask allows for safe and effective mixing of the reactants by swirling.

So we can swirl that without risk of any of the liquid coming out of the top of the conical flask, or it reduces that risk.

So here's a question based on that learning.

What is the primary function of a burette in a titration? Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answer to that question is to measure and deliver the acid or base drop by drop.

So well done if you got that correct.

Second question.

What is the primary function of the volumetric pipette in a titration? Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answer to that question is to accurately measure a fixed volume of solution.

We need to use suitable indicators in titration, and you will have used different indicators before, probably very familiar with litmus, for example, a universal indicator.

But titrations use very specific indicators, and this is because they have what's called an end point.

So indicators like phenolphthalein and methyl orange are preferred over universal indicator because they have a clear and distinct colour change at the end point of the titration.

So when neutralisation occurs, there is a change in colour that's very clear.

So phenolphthalein goes from colourless in acid to pink in alkali, and methyl orange is red in acid and yellow in alkali.

So you can see this changing colour at neutralisation as it changes from an acid to an alkali.

So true or false question.

Universal indicator is preferred over phenolphthalein and methyl orange in titrations.

Is this true or false? And then justify your answer using the statements below.

Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answer is false.

And this is because universal indicator has got a wide range of colours with no clear end point.

So well done if you got that correct.

What is the colour change of phenolphthalein when titrating a base in the flask with an acid in the burette? Now remember, the indicator is placed into the flask, so you need to think about what colour would it be at the start when it's added to a base, and what colour will it turn to when eventually that solution reads neutralisation and tips over into acidic.

Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So firstly, we can discount A and B because they are changes for methyl orange.

We know it's either C or D, and the answer is C, pink to colourless, because phenolphthalein is pink in a base and colourless in an acid.

So well done if you got that correct.

Now, titration allows us to add the perfect volume of acid to base or vice versa to achieve complete neutralisation so we'll know the precise volume we need to add to a solution to neutralise it.

And this precise method produces soluble salts without any excess reactants left in the reaction mixture.

So we've got no reactants left at all, just the products.

So when making a pure sample of salt, a second titration is performed without the indicator.

And this is because the indicator can contaminate the salt at the end.

And what we want is just salt and water being produced at the end, and we don't want any reactants leftover.

So we can use those exact volumes from the first titration to do that.

So here's a true or false question based on that learning.

The first titration is performed without an indicator to ensure a pure sample of salt is obtained.

Is that true or false? And then justify your answer using the statements below.

So pause the video here and I'll see you when you finished.

Welcome back.

So the answer to that question is false, and that's because the first titration must be run with an indicator to measure the volume of solution needed for neutralisation.

If the indicator wasn't present, we wouldn't know whether neutralisation had occurred or not, and therefore we wouldn't know the precise volumes that we needed for that neutralisation reaction.

We're now going to do Task A and we've got three questions.

So what is meant by the following terms? A pupil add sodium hydroxide solution, drop by drop, to a solution of hydrochloric acid and methyl orange.

What colour change will they observe, if any, and why? And then three, when making a pure sample of a soluble salt, why must the titration be repeated after determining the volume of base required to neutralise the acid? So pause the video here, answer those questions, and I'll see you when you're ready.

Welcome back.

So let's go through those answers one at a time.

And here are the definitions for those particular terms. So a strong acid is one that completely ionises in water, meaning it dissociates fully into its ions.

A base is a substance that can neutralise an acid, making a salt and water.

A soluble salt is a salt that dissolves in a solvent, such as water.

Excess reactant, the substance that's present in a greater amount than is necessary to completely react with the other reactants.

That means it's leftover at the end of the reaction.

And the end point, the point at which the reaction between an acid and a base is complete as indicated by a change in the colour of the indicator used.

And you might have used an example there.

Well done if you got that correct.

Let's move on to question two.

A pupil adds sodium hydroxide solution, drop by drop, to a solution of hydrochloric acid and methyl orange.

What colour change will they observe, if any, and why? So the pupil would observe a colour change from red to orange and then to yellow.

Methyl orange is red in acidic solutions such as hydrochloric acid.

As sodium hydroxide is added, the solution gradually becomes less acidic, turning orange as it approaches neutral, and then finally turning yellow when it becomes slightly alkaline.

So again, well done if you got that correct.

Question three.

The titration must be repeated without an indicator to produce a pure sample of the soluble salt.

The initial titration with the indicator determines the exact volume of acid and base needed to reach the end point.

However, the indicator could contaminate the salt, so the process is repeated using the same volumes but without the indicator to ensure the resulting salt is pure.

So well done if you've got something similar to that.

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

Actually performing a titration, carrying one out.

So when conducting any experiment, never assume that the equipment is ready to use or free of contamination.

Rinsing all equipment with water may seem logical, but tap water contains dissolved salts that can interfere with a reaction.

And titration relies on specific volumes, any water used will dilute reactants and alter the volumes used and the recordings that you've made.

So you need to be careful.

Here's a true or false question based on that learning.

Tap water is suitable for rinsing chemical apparatus.

True or false? And justify your answer.

Pause the video here and I'll see you when you finished.

Welcome back.

So the answer is false.

And that's because tap water contains dissolved salts.

The burette should be rinsed with the chemical it is to be filled with not with water.

This ensures no dilution occurs when the burette is filled.

And once filled, always record the initial volume accurately to two decimal places, the last being either a zero or a five.

So it should always be to two decimal places, and that final number should always be either a zero or five.

It's different to how you might record other data.

And never fill a burette above eye level.

So you need to move the burette down so that it's at eye level.

This avoids accidents.

The volumetric pipette or the measuring cylinder, depending which equipment you've got available, should be rinsed with the solution it will contain as well.

And this prevents dilution by water that's left over inside the measuring cylinder, and that ensures that your volume measurement is accurate.

But you need to be careful when filling the pipette if you're using one of those, 'cause you need to get the volume up to the marked line to ensure that volume is accurate.

The conical flask can be rinsed with either the water or the same solution as is in the volumetric pipette.

And this is because the volume of the solution is measured before it's transferred to the flask.

So any minor dilution from rinsing won't affect those recorded measurements.

So here's a question based on that learning.

Why should a burette be rinsed with the chemical it was filled with rather than water? So pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So that is to avoid dilution of the chemical.

Well done if you've got that correct.

Here's a true or false question based on that learning.

A conical flask can be rinsed with water before being filled with an acid or a base in a titration.

Is this true or false? And justify your answer.

Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answer is true.

And this is because the volume of solution is measured before it's transferred to the flask.

So well done if you got that correct.

The solution is transferred from the volumetric pipette to the conical flask, and then a number of drops of suitable indicator such as phenolphthalein or methyl orange is then added.

Remember, that's an end point indicator.

With the burette set up and the conical flask containing the solution, the solution is slowly added from the burette to the solution in the flask while swirling the flask continuously.

And that makes sure that the chemicals are actually mixed together correctly.

As soon as the indicator changes colour, so when you see that end point has been reached, the burette top is closed immediately, and then we get the final volume of the burette and we record that.

So we'll have the initial volume and the final volume, and we can determine the volume of the solution that's used at that point.

So tips for accurate and effective titration.

Now have a look at the scale there.

We're looking at the bottom of the meniscus.

That's the curved surface of the liquid.

So we need to ensure that the solution is added drop by drop as you approach the end point to avoid overshooting the reaction.

So you all don't wanna get past the end point.

So we're doing it very gradually.

We need to keep swirling the conical flask to mix the solutions thoroughly, and that ensures the reaction occurs evenly.

And we always read the meniscus at eye level for both the initial and the final volumes to maintain accuracy.

And that prevents something called parallax error.

So our eye needs to be level with that meniscus to prevent parallax error.

Here's a question based on that learning.

When should you stop adding the solution from the burette to the conical flask? So pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answers to that question is when the indicator changes colour.

That indicates the end point of the reaction.

Second question.

Why is it important to swirl the conical flask while adding the solution from the burette? Pause the video here, answer the question, and I'll see you when you finished.

Welcome back.

So the answer to that question is to ensure even mixing of the reactants.

So well done if you got that correct.

We are now going to do Task B, which is to actually carry out a titration, and you'll require the additional materials that contain the method.

You're gonna complete a titration to neutralise a solution of hydrochloric acid and sodium hydroxide.

Both are 0.

1 molar or 0.

1 moles per decimeter cubed.

And you're gonna use phenolphthalein indicator.

Record your results and observations in a table like the one below, and note the order under the burette readings.

We got the final volume, the initial volume, and then the calculation, which is the total volume added, and we've also included the colour at the end point as well.

So carry out that titration and I'll see you when you finish so we can compare your results to mine.

Welcome back.

So let's have a look and see what your results table may look like.

So here we've got the final volumes and the initial volumes.

Now check your results.

Have you included a zero or a five at the end? And are they altered to two decimal places? And you need to do that for your total volume added as well.

And then you've got the colour at the end point, should all be colourless.

So well done if your table looks something like that.

Here's a summary of today's lesson.

Titration is a method used to completely neutralise an acid with a soluble base or an alkali.

Titrations are performed using strong acids and strong alkalis to accurately determine reacting volumes.

Strong acids and alkalis are completely ionised in aqueous solution.

Each piece of apparatus in titration has a specific and essential function.

A suitable indicator, not universal indicator, is used to identify the end point of the titration.

And this, remember, is either normally phenolphthalein or methyl orange.

Thank you very much for joining me for today's lesson.