Hello, my name is Mrs. Collins and I'm going to be taking you through today's learning.

This lesson forms part of the unit "Making salts" and is called "Titrations: analytical techniques." During today's lesson, you're going to learn how to accurately measure the volume of an acid of an unknown concentration that neutralises an alkali of a known concentration.

Here are the keywords for today's lesson.

Titrant, analyte, concentration, concordant, and titre.

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

Today's lesson will be split into two separate parts, "Titration as an analytical technique" and "Performing a titration." So let's start with the first part of the lesson, "Titration as an analytical technique." Titrations are used to determine the exact volume of one solution needed to react completely with another solution.

This technique helps us identify unknown concentrations in solutions, making it a valuable tool in analytical chemistry.

In a titration, two key solutions are involved.

The titrant, this is the solution of known concentration which is added gradually during the titration, and we place this inside the burette.

And the analyte, this is the solution of unknown concentration which is being tested, and we put this in the conical flask.

The goal of a titration is to find out exactly how much titrant is required to completely react with the analyte.

True or false question based on that learning.

Titrations are used to determine the exact volume of one solution needed to react completely with another solution.

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

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

Welcome back, so the answer to that question is true.

One solution is added via burette to another solution in a conical flask, so well done if you got that correct.

Here's the second question.

Which of the following accurately describes the titrant in a titration? Pause the video here, read through the statements, decide which one is correct, and I'll see you when you're finished.

Welcome back, so the answer to that question is C, the solution of known concentration, which is added gradually during the titration.

So well done if you got that correct.

Before performing the precise titration, a trial investigation is completed.

This helps to estimate how much titrant is needed to neutralise the analyte.

Remember, the titrant is in the burette and the analyte is in the conical flask.

By doing a rough titration first, we can make the actual titration more accurate.

As the titrant is added to the analyte, the solution gradually reacts.

Near the end point, the titrant is added drop by drop.

And swirling the conical flask ensures even mixing and an accurate determination of when the reaction is complete.

Remember that from a previous lesson.

Here's a question based on that learning.

What is the purpose of performing a trial investigation before the precise titration? Pause the video here, answer the question, and I'll see you when you're finished.

Welcome back, so the answer to that question is to estimate how much titrant is needed to neutralise the analyte.

Well done if you got that correct.

Why is it important to add the titrant drop by drop near the end point? Pause the video here, answer the question, and I'll see you when you're finished.

Welcome back, so the answer to that question is to ensure even mixing and an accurate determination of the end point.

So well done if you got that correct.

A suitable indicator like phenolphthalein or methyl orange is chosen to measure the end point, but for greater accuracy and precision we could use a pH metre to detect the exact pH when neutralisation occurs.

Placing a white tile under the conical flask improves the visibility of the colour change during titration, especially if you're using a chemical indicator like phenolphthalein or methyl orange.

It can make it easier to spot the exact moment when the end point is reached.

So which of the following statements are correct? Pause the video here, answer the question, and I'll see you when you're finished.

Welcome back, so the answer to that question is methyl orange is red in acidic solutions and yellow in alkaline solutions.

And a pH metre can detect the moment of neutralisation more accurately than a chemical indicator.

So well done if you got that correct.

To ensure precise volume measurements, always read the volume at the bottom of the meniscus with your eyes level with the burette, and what this does is it reduces parallax error and it helps you to record precise data.

So we can see that here on an actual image of a burette.

Which of the following practises help ensure accurate volume measurements when using a burette? Pause the video here, answer the question, and I'll see you when you're finished.

Welcome back, so the answer is reading the volume at the bottom of the meniscus, keeping your eyes level with the burette when taking a reading, and adding the titrant drop by drop near the end point.

So well done if you got that correct.

We're now going to do Task A.

So for question one, define those terms. And for question two, sort the steps into the correct order.

The first has been done for you.

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

Welcome back, so let's go through those answers.

Firstly, the definitions.

The titrant is the solution of known concentration that's added from the burette during titration.

The analyte is the solution of unknown concentration in the conical flask that's being tested.

Concordant, these are the titrant values that are typically within 0.

10 centimetre cubed of each other, indicating consistent results.

And the titre is the volume of titrant used to reach the end point in a titration.

Question two, so step one was done for you, measure 25 centimetre cubed of the analyte into the conical flask.

Two, record the initial volume of the titrant.

Three, swirl the conical flask to mix the solutions.

Four, add titrant drop by drop near the end point.

And five, record the final volume of the titrant.

Here is the second part of the lesson then, "Performing a titration." So in titration, we're collecting accurate data because it's crucial for determining the unknown information such as the concentration of the analyte in the conical flask.

When taking readings from the burette, it's important to record the volume to two decimal places for precision.

And remember, the final value for that is either 0 or 5.

The first decimal place is determined by the smallest graduation on the burette.

Normally this is 0.

1 centimetre cubed.

The second is an estimate and it can either be 0 or 5, as I mentioned.

If the meniscus is exactly on the graduation mark, the reading should end in 0.

So for example, in this one we've got 25.

40.

If the meniscus is anywhere between the two graduation marks, we record it as 5.

So this example, 25.

65.

Here's a question based on that learning.

How should you record a burette reading if the meniscus is exactly on a graduation mark? Pause the video here, answer the question, and I'll see you when you're finished.

Welcome back, so the answer to that question is D, record the reading to two decimal places ending in a 0.

Onto the second question, what would the volume be recorded as on the burette shown below? So have a look at that image, determine what you would record in your results table.

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

Welcome back, so the value would be 12.

45.

And remember, we're ending in a 5 because it's partway between those graduations.

So the titre is the volume of titrant used to reach the endpoint in a titration.

Each time you perform a titration, you record the titre by subtracting the initial volume of titrant from the final volume in the burette.

The accuracy of your titration depends on obtaining concordant titres.

That means consistent titres.

Concordant titres are titres that are within a small range of each other, and normally this is plus or minus 0.

10 centimetre cubed.

When you achieve concordant titres, it indicates that your technique is consistent and your data is reliable and you can stop taking readings.

Titres that fall outside this range should be excluded from your calculations.

Here's a question based on that learning.

What is the significance of obtaining concordant titres in a titration? So pause the video here, answer the question, and I'll see you when you're finished.

Welcome back, so the answer to that question is it indicates that your technique is consistent and your data is reliable.

So well done if you got that correct.

Second question, which of the following statements about titres that fall outside the range of concordant titres are correct? Pause the video here, answer the question, and I'll see you when you're finished.

Welcome back, so the answer is they indicate potential errors in your technique and they should be excluded from your calculations, so well done if you've got that correct.

We're going to do Task B now and you will need the additional materials where you'll find the method and you're going to perform a titration.

So you're going to complete a titration to completely neutralise the solution of hydrochloric acid and sodium hydroxide, and we've got a concentration of 0.

1 moles per decimeter cubed of hydrochloric acid and an unknown concentration of sodium hydroxide.

You're going to use phenolphthalein as an indicator until you have at least two concordant results.

So we're looking for results that are within plus or minus 0.

1 centimetre cubed of each other.

You're gonna record your results in a table like the one below, with the final volume on top and the initial volume at the bottom, and then the titre is the difference between the two.

Pause the video here, carry out the experiment, and I'll see you when you're finished.

Welcome back, so let's see how your results compare to those that we've got on the screen here.

So I've got concordant titres there that are within plus or minus 0.

1 centimetre cubed of each other.

And I've recorded all my values to two decimal places and the final value is a 0 or a 5 in each of those readings.

So well done if your results look something like that.

Here's a summary of today's lesson.

A trial investigation helps estimate the amount of acid needed to neutralise the alkaline.

Near the end point, add the acid drop by drop while swirling the solution in the conical flask to mix.

Placing a white tile under the conical flask enhances the visibility of the colour change and the accuracy of the readings.

Volume readings should be taken at eye level from the bottom of the meniscus.

And concordant titres are typically within plus or minus 0.

10 centimetre cubed.

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