Welcome to today's lesson.

Today we're going to do a practical, which involves us adding some base to a fixed volume acid and looking how that affects the pH.

We're going to record the results in a suitable table, and we're going to analyse those results.

So my name's Mrs. Clegg.

This lesson's part of the units on making salts.

So let's get started.

Here's our lesson outcome.

By the end of it, you should feel much more confident in being able to investigate the change in pH when we add a base to a fixed volume of acid.

Here are our key words for today.

So pH is a measure of the hydrogen ion concentration in a solution.

Neutralisation is a chemical reaction between an acid and a base to produce a neutral solution of a metal salt and water.

A base remember, is a substance that neutralises an acid to form salt and water.

And then we've got this word quantitative and that refers to a measurement of quantity, a number, a numerical value.

Our lesson today is split into two parts.

We're going to look at the planning first of all, and then we're going to look at how to analyse our results.

So let's get started with the planning.

Neutralisation, if you remember, is a reaction that involves an acid and a base producing a salt and water.

Two of the common bases that we use are hydroxides or oxides.

So here we've got two examples, actually producing the same salt, calcium chloride, but in two different ways.

So in the first one, we've got calcium oxide, an acid, hydrochloric acid producing calcium chloride and water.

Or we could use calcium hydroxide and hydrochloric acid to also produce calcium chloride and water.

Quick check.

So neutralisation reactions involve an acid reacting to produce a salt and water.

Is that true or is that false? Well done, if you said true, can you justify your answer? So if we have a look at these, acids always react to produce a salt and water is not true.

An acid must react with a base to produce salt and water is true.

So well done if you said B.

Universal indicator or a pH metre can be used to give us a quantitative figure for pH, that would be a number.

And that tells us how acid or alkaline something is.

And if we look at the image here, we can see the colour chart, the colour reference chart for universal indicator.

And anything with a pH that's less than seven is acidic.

And anything that with a pH that's greater than seven is alkaline.

And anything with pH seven is neutral.

And you can see the different colours there.

And you should have a good idea that if something turns universal indicator solution red or orange or yellow, that it will be acidic.

And if it turns it blue or purple, it's going to be alkaline.

Let's have a quick check.

So at what pH is a solution considered to be neutral? Well done if you said B, pH seven.

During a neutralisation reaction, the pH of the solution changes as we add base to the acid.

The solution will start with a low pH, which indicates high acidity and the colour on the reference chart there would be sort of those reds or oranges.

And as we add more base, the pH will gradually increase as the acid is neutralised.

When the pH reaches seven, the acid is completely neutralised.

If we add more base, then the solution will become alkaline and the pH will rise above seven.

So adding the base in really small amounts, first of all, is crucial for accurately tracking the change in pH and being able to precisely identify the point at which we achieve neutralisation and 0.

30 grammes might be a suitable amount.

So let's have a check.

What happens to the pH of a solution during a neutralisation reaction as a base is added to an acid? Well done if you said the pH gradually increases.

Remember, pH less than seven is acid and pH greater than seven is an alkali.

Now, to conduct the experiment effectively, we need a good well-planned method.

Writing a clear and detailed method ensures that the experiment is both reproducible and accurate, and it should include: the apparatus and chemicals that we're going to use.

And we should specify the type and concentration of any substances that we're going to use.

We should specify the quantities and measurements such as the volume of acid and the mass of the base.

Instructions on how to add substances are important.

How to measure pH and how to record any observations should be given.

Any safety equipment that's required and specific precautions that we need to know when we're handling chemicals.

So you know and remember, acids and bases are both corrosive should also be specified in the method.

So here's an example.

This is an experiment to investigate the effect of citric acid on sodium bicarbonate solution.

Got, first of all, let's have a look for apparatus and chemicals.

So there we can see, we're looking at 0.

1 molar sodium bicarbonate solution.

We are going to use a measuring cylinder and we're going to use a beaker.

We're going to use universal indicator paper, citric acid powder, and a glass rod.

So that's telling us the apparatus and chemicals we need to collect.

Then we're going to look at the quantities that we're going to use.

So there we can see we need 50 centimetre cubed of the sodium bicarbonate.

We need 0.

50 grammes of citric acid powder, and we're going to add the citric acid in 0.

50 gramme increments until we've added a total of five grammes.

So that tells us the quantities and measurements.

And here we've got a safety recommendation that we should be wearing safety glasses.

Let's have a quick check.

So which of the following should be specified in the method for an experiment? Which of these do you think? How did you do? Well, it was a bit of a trick question really, I suppose because we need all of them.

Let's have another look at another question.

So true or false, safety equipment is not needed when handling chemicals in a neutralisation experiment.

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

And can you justify why that is a false statement? Well done if you said B, acid and basis are both corrosive.

So they both pose a danger that could, both of them could cause harm.

So let's have a look at how we should record our results for this experiment.

It's really crucial to enable us to accurately record and analyse data to have a really well organised table.

It enables us to compare and to track changes in pH during the experiment.

Ensure each column has a heading that includes the variable name and the units if they're applicable.

So pH, for example, we wouldn't be using any units.

You need to arrange the table logically, and typically we put the independent variable in the first column and the dependent variables in later columns.

Can you remember what the independent variable and dependent variable mean? So the independent variable is the variable that we as the scientists have chosen to alter.

So in this case, it's going to be the mass of citric acid and the dependent variable is the variable that we are going to test or measure.

So that will be pH in this experiment.

And of course, the control variables are the factors that we choose to keep the same during the experiment.

So let's have a look at an example of a table.

So here's a table that you could use.

We've got some great headings there.

For the independent, independent variables.

We've got the name of the variable and the units included where they're relevant.

Remember that pH, we're not going to use units there.

And we've got all the possible readings in our table here for the mass of citric acid.

'Cause we were going to increase in increments of 0.

50 grammes.

So we've got all of those there.

So that's a pretty good table.

Let's have a quick check.

So why is an organised results table important in an experiment? Well done if you said D, it helps in accurate recording and enabling us to analyse the data much more easily.

Let's have a look at task A.

So you are going to investigate how pH changes when powdered calcium hydroxide is added in 0.

30 gramme increments to a maximum of three grammes to dilute hydrochloric acid.

I want you to write a method for this practical investigation.

Don't forget to include the names of the apparatus, any safety precautions we need to take and the quantities of substances that we need.

Also, I want you to design a results table that'll be ready to record your observations and results and then complete the investigation after your teacher has seen your method and checked it.

So pause the video and join us when you've written your method, had it checked by your teacher, created your results table, and carried it out.

Okay, welcome back.

Let's first of all have a look at part one, which was writing a method for the investigation.

So we can see in the method we've got a safety precaution to wear safety glasses.

We have decided we're going to use 0.

1 molar dilute hydrochloric acid.

We're going to add increments of 0.

30 grammes of calcium hydroxide powder to the acid.

We're going to use 25 centimetre cubed of acid and we're going to stir and we're going to record the pH after every addition of calcium hydroxide and will carry on until a maximum of three grammes of calcium hydroxide has been added to the dilute hydrochloric acid.

So there's a method that would work.

Yours hopefully is similar.

So let's have a look at a sample results table now.

There we go.

So we've got some good headings, the mass of calcium hydroxide added in grammes.

We've got the colour of the universal indicator paper and we've got the corresponding pH.

We can see that we've added the calcium hydroxide in 0.

30 gramme increments, and we've gone right up to three grammes and the pH has changed from being acidic to being alkaline.

Let's move on to the second part of the lesson, which is analysis.

So accurately recording and plotting our data is essential for being able to visualise changes and trends in our experiment.

A really well-constructed graph helps us to spot these trends very easily.

So here's a graph showing the average rainfall and temperature each month for a place in the UK called Coventry, and we can easily see the trends there in terms of temperature and rainfall.

This is a graph that's got two Y-axis, if you notice.

Let's do a quick check.

So a sketch graph is as useful as a detailed, well-constructed graph.

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

And can you justify that? The reason that we would use well-constructed graphs is to enable us to spot trends in our data.

A well-constructive graph does indeed look more professional and more scientific, but the reason that we do this is to enable us to look at trends because that's what we're looking for.

And we also need to think about the accuracy and the limitations and the potential errors that we might have in our experiment because that helps us understand the reliability of our results.

So calcium hydroxide, for example, is not actually that soluble in water.

So whilst we're doing the practical, we need to keep mixing the solution to make sure that we're getting accurate pH readings.

And the use of universal indicator paper can introduce errors too.

The way that I interpret a colour might be different to the way you do.

So a digital pH metre would be much better to give us more accurate readings.

Let's do a quick check.

So why is it important to discuss the accuracy, limitations, and potential errors of your experiment? So A, understanding the reliability of your results, definitely.

To make the experiment seem more complex in B, seems rather odd.

Why would we try and make things more complicated than they are? So not sure about that one.

To identify ways to improve future experiments, absolutely.

So scientists are always looking for ways to improve the experiment, to improve the accuracy.

And D, to provide a complete evaluation of your experimental method.

Yes, because that basically means we are looking at the potential errors and the limitation and the accuracy and so on.

So yes, so the answers are actually A, C and D.

Well done if you've got all of those correct.

Let's have a look at task B.

So now you've collected some data.

I would like you to plot that data on a graph to visualise the change in pH as you add calcium hydroxide.

Think about what will go on the X-axis and what will go on Y-axis.

I want you to analyse the graph to identify the point of neutralisation.

In other words, what mass of calcium hydroxide do you need to neutralise the acid? And then write a conclusion based on your findings and discuss any anomalies, any results which don't fit the pattern.

And finally, part four, write an evaluation of the practical and suggest possible improvements if you were to do this experiment again.

Pause the video and come back when you are ready.

Okay, let's have a look.

So here's a graph plotted from the sample results.

We've got the independent variable on the X-axis, the mass of calcium hydroxide that we added.

We've got pH on the Y-axis.

We've plotted all the points and decided on the line of best fit.

So if we look at the graph, we can identify where pH seven lies, and so we can actually identify the mass of calcium hydroxide that we need to bring about neutralisation.

And in the sample results, it's 2.

40 grammes.

I wonder how your results compare to mine? And then you were asked to write a conclusion.

So here's a potential conclusion.

Initially, the pH of the solution increases slowly as small increments of calcium hydroxide are added.

After 2.

10 grammes of calcium hydroxide are added, there is a sharp rise in pH.

pH levels off at pH ten, when around 2.

70 of calcium hydroxide is added.

The neutralisation point for the reaction between calcium hydroxide and dilute hydrochloric acid occurs at approximately 2.

40 grammes of calcium hydroxide.

Let's have a look now at an evaluation of the practical.

So the accuracy of the experiment could be improved using a pH metre instead of universal indicator paper.

There might have been inconsistent mixing due to the low solubility of calcium hydroxide and that might have affected the results.

And so ensuring thorough mixing after each addition would enhance the accuracy.

And conducting multiple trials, so repeating the tests and being able to calculate an average would help minimise errors and improve reliability.

Well done, let's have a look at the summary of today's learning.

So when powdered hydroxide or oxide is added to an acidic solution, there will be an increase in pH.

pH changes quickly around the neutralisation point, which is why you need to add dropwise to make sure that you don't miss the neutralisation point if you are using solutions.

And indicators such such as universal indicator paper can give us quantitative data on pH, but even better would be the use of the digital metre, digital pH metre.

And we've also looked at plotting the change in pH on a graph to actually be able to find the quantity of the base we need to neutralise an acid.

So amazing, well done for sticking with it and I'll see you next lesson.