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

This forms part of the unit, Energy Changes in Reactions, and we are going to look at a neutralisation practical today.

During this lesson, we're going to learn how to perform a practical to measure the temperature change in a neutralisation reaction, how to record the results, analyse the data, and conclude if the reaction is exothermic or endothermic.

Here are the key words for today's lesson; neutralisation, exothermic, method, line graph, and conclusion.

Now, most of those words will be familiar to you, but pause the video now, have a look through those descriptions and make any notes you feel you need to.

Today's lesson is divided into three separate sections.

First of all, we're going to talk about how to write a method.

Then we're going to look at the investigation itself, and then we're going to analyse the data produced and draw a conclusion.

So let's start with writing a method.

So neutralisation reactions, remember, involve an acid reacting with a base to form a salt and water.

So for example, we have hydrochloric acid reacting with sodium hydroxide to form sodium chloride, which is the salt plus water.

During neutralisation reactions, the temperature of the solution will change, and this energy change can be measured using calorimetry.

So remember, calorimetry is the method that we use to carry out the investigation and the temperature of the solution is the surroundings in this experiment.

Once one of the reactants is used up, the reaction is complete.

Most neutralisation reactions are exothermic.

For example, the reaction between a strong acid and a strong base.

Some neutralisation reactions involve weak acids and weak bases.

And these may be endothermic reactions because they may absorb energy overall rather than releasing it.

This means that while most neutralisation reactions are exothermic, a few can be endothermic.

We are now going to complete a question.

Look at the following equations.

Which one is written correctly? Pause the video here, have a think about your answer, and I'll see you when you're finished.

So hopefully you recognise that the only equation there that's correctly balanced is C.

So we need to make sure that we've got the same number of atoms of each element on one side of the equation as we have on the other side of the equation.

So it needs to be balanced.

Well done if you got that correct.

Before conducting the neutralisation practical, a hypothesis needs to be written.

So the hypothesis should state what could happen when a strong base is added to an acid, and then suggest why this will happen based on knowledge of neutralisation reactions.

So let's have a go at writing a hypothesis together and then you are going to write one by yourself.

So when sodium metal is reacted with oxygen gas, the mass of the solid will.

This will happen because.

Now, we need to think the sodium is reacting with oxygen in the air.

So the mass of the solid will increase.

This will happen because the mass of the oxygen reacted will be added to that of the sodium to form sodium oxide.

So the mass of the sodium oxide is equal to the mass of the sodium at the start, plus the mass of the oxygen at the start that it reacted with.

So now you have a go at writing our hypothesis.

So when the base, sodium hydroxide, is added to hydrochloric acid, the temperature of the solution will.

This will happen because.

So pause the video here and have a go at finishing off those sentences.

So hopefully you've predicted that the temperature of the solution will increase.

This will happen because the neutralisation reaction between a strong acid and a strong base is exothermic and energy will be released to the surroundings.

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

So before conducting any practical, we need to think about the variables involved in that practical, and they come in three different forms, remember? So we have the independent variable.

This is the one you control, you change.

The dependent variable, the one you measure during the practical activity and the controls, the ones that you keep the same to ensure that you're carrying out a fair test.

And this practical we're going to do is going to investigate the temperature change, which occurs when different volumes of sodium hydroxide solution are added to hydrochloric acid solution.

So let's think about what each of the variables might be for this investigation then.

So which of the following is the independent variable for the displacement practical? So have a think about that, pause the video and then I'll see you when you're finished.

So the independent variable in this investigation is the volume of the sodium hydroxide solution.

So that's the one that we are going to change during the investigation.

Which of the following is the dependent variable for the neutralisation practicals, the one we're going to measure during the practical itself.

So again, pause the video, answer the question, and I'll see you when you're finished.

So the dependent variable for this investigation is the temperature change of the neutralisation solution.

So remember, it's not the temperature of the surrounding atmosphere, but the temperature of the neutralisation solution.

So well done if you got that right.

And then we need to consider control variables for the neutralisation practical.

So there may be more than one here.

So pause the video again, consider the answers and then I'll see you when you're finished.

So for this investigation, the ones that we're going to control are the volume of the acid solution, the concentration of the acid solution, and the concentration of the sodium hydroxide solution.

Remember, the temperature change is the dependent variable.

We can think of a method like we do a recipe for making a cake.

So it needs to have equipment detailed as a list or even a label diagram.

Sometimes a labelled diagram is more effective.

Details of the reactants that we are going to use.

A simple, easy-to-follow step-by-step set of instructions.

And the neutralisation method will detail how to use calorimetry to measure temperature changes which occur when small volumes of sodium hydroxide solution are repeatedly added to hydrochloric acid solution.

So if you remember, we talked about calorimetry in a previous lesson, and we mentioned that this is where the reaction takes place in an insulated container like a polystyrene cup.

And you might remember this image here.

And we measure the initial temperature of the reactant that's placed in there.

And for an exothermic reaction, we measure the highest temperature recorded when the other reactant is added.

And if we were doing an endothermic reaction, we would measure the lowest temperature that was reached.

So now we're gonna have a go at task A.

So complete the following tasks required to write a method describing how to use calorimetry to measure temperature changes which occur when small volumes of sodium hydroxide solution are repeatedly added to a hydrochloric acid solution.

So have a go at A and B.

It'll take you a little while.

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

So let's go through the answers.

So first of all, a list of reactants.

So you've got hydrochloric acid solution and sodium hydroxide solution, and it's quite useful here to give concentrations as well.

So maybe they might both be two moles per decimeter cubed, for example, or one mole per decimeter cubed.

We are going to need different size measuring cylinders.

So you might have given the sizes of those.

And then it's always good to draw a label diagram 'cause it does make sure you don't miss out any pieces of equipment.

So you do need a thermometer, polystyrene cup and lid, the beaker, remember, to stabilise it to help prevent it being knocked over.

And then your acid solution inside the beaker ready to be measured in terms of the temperature.

So now we're gonna have a step-by-step method.

Now, here's the method that we've got written down here, but yours might differ slightly and there's a few particular areas where it may, but first of all, you need to set up the equipment as in the diagram.

That's the first step.

And then the second step is adding the hydrochloric acid solution to the polystyrene cup.

And you need to specify a volume here.

And we've written w because there's no particularly correct answer here.

So you could have, you know, 5, 10, 15, 20 centimetre cubed.

So an actual volume of hydrochloric acid.

Now, importantly, when we measure the initial temperature for Step 3, we need to do that before the sodium hydroxide is added.

So make sure that's right in your method.

Then you are going to measure a particular volume of sodium hydroxide solution and add it and then stir, make sure you've remembered to stir the solution, and then measure and record the highest temperature reached.

And then you're going to repeat the method with different volumes of sodium hydroxide solution.

So you might have gone from five centimetre cubed to 10, to 15, to 20, for example, or maybe 2, 4, 6, 8.

But make sure that your volumes have increased by a sensible amount each time.

We are now moving on to the second part of the lesson.

So this is investigating the neutralisation energy changes.

So we've done the method, we've thought about the variables and we thought about our hypothesis.

So now we're going to move on to actually carrying out the practical itself.

So remember, the method that we're going to use is involving this polystyrene cup and lid and the beaker.

And here's the set method that we're suggesting is carried out.

So 30 centimetre cubed of hydrochloric acid, 10 centimetre cubed of sodium hydroxide, and then gradually increasing the volume of sodium hydroxide until we get to 80 centimetre cubed of sodium hydroxide.

So before performing the investigation, we need to design a results table that fits with our method and the independent variable needs to be in the first column.

And all the further columns need to record the dependent variable.

So might be the volume of gas produced, for example.

And in our case, we are thinking about temperature, and we must show all of the units in the top of the table.

So here's a good example.

We've got time in seconds and volume of gas produced in centimetre cubed.

So this is obviously not a results table relating to this practical, but it gives you a good example.

So for task B, what you want to do, first of all, is design this results table for the investigation.

So the neutralisation investigation will measure the the temperature change, which occurs when small volumes of sodium hydroxide solution are repeatedly added to hydrochloric acid solution.

So think about the first column and the independent variable and then what the other columns might be in that results table.

So pause the video here and design your results table for that practical.

Welcome back.

So let's have a look at the suggested results table for that practical then.

Here it is, it could look like this.

So we've got the volume of sodium hydroxide added in the first column.

So we go 0, 10, 20 30, and that'll carry on to 40, 50, 60, 70 80, which is what the.

80 means.

And then you could record the highest temperature reached.

You might also want to have a column that's got the initial temperature as well.

So there's lots of different potential correct answers here.

For Question 2, we're going to perform the investigation involved in the neutralisation reaction and we're going to repeat the experiment three times and record the results in the table as followed.

What we're going to do is watch someone carrying out the investigation so that you can see and record some of their data.

And we're gonna record the results in the table.

So let's watch the video of the experiment taking place.

<v Instructor>Firstly, we are going</v> to place 30 centimetre cubed of hydrochloric acid into the insulating cup and measure the initial temperature.

We're now gonna add sodium hydroxide in 10 centimetre cubed portions.

So that's our first 10 centimetre cubed.

So note the temperature.

Now we're gonna add our second one.

Note the temperature.

Our third.

Note the temperature.

And fourth.

Note the temperature.

Fifth.

Note the temperature.

Sixth.

Note the temperature.

And lastly, the seventh, making a total of 70 centimetre cubed.

Note the temperature.

We are now adding excess sodium hydroxide, five centimetre cubed.

Note the temperature.

<v ->So hopefully you've recorded data</v> in your results table and your results table may well look something like this.

So this is a set of data here and it's recorded in the table.

So however you've recorded it, whether you recorded it from the video or carrying out your own investigation, hopefully it looks something like that.

Now we're gonna move on to the third part of the lesson.

We're going to be looking at data analysis and conclusion.

So once data from an investigation have been collected, they need to be analysed.

And this process involves identifying any anomalous results and calculating the mean and the uncertainty of each volume of sodium hydroxide added.

Presenting the data clearly in a line graph.

Interpreting what the data are showing and concluding whether or not the hypothesis was correct and why it is correct or why it's not correct.

And then lastly, we might evaluate how to improve the investigation to produce more reliable data.

So an anomalous result is a result that doesn't fit with a pattern of the other results.

And these are removed when we carry out a mean calculation.

So if you look at the value for a mass of 100 grammes, we've done three different trials, we've done three different repeats and then calculated the mean for that.

Now if you look at the values for 200 grammes, we can see we've got 11.

3, 11.

5, and then 13.

9.

Now, 13.

9 looks like it's an anomalous result.

It doesn't quite fit the pattern of the other two pieces of data.

So what we would do then is calculate a mean from 11.

3 and 11.

5, and we come up with an a value of 11.

4.

So we wouldn't include the anomalous result in our data calculation for the mean.

And we place 11.

4 in the results table.

So we are going to find the mean of some different masses here, and I'm going to talk you through this example and then you will carry out one by yourself.

So we've got four different masses here, 25, 22, 24, and 27, and we're going to find the mean of these masses.

So the first thing we do is we add up those four values and divide it by the number of values we have, which is four.

This will give us a value of 24.

5 grammes.

And then we need to think, well, we need to do that to nought decimal places.

'cause we need the value to the same number of decimal places as the original values.

So that will round up to 25 grammes.

So now you are going to carry out calculation.

So here we've got a series of different temperatures.

These are temperature measurements, and what you need to do is find the mean of those temperature measurements.

So pause the video here and calculate the mean, show your working for the calculation.

So the first step is to write down all of the numbers for those temperatures and divide it by how many we have.

So this time, we've got five different temperatures.

That gives us a value of 30.

2.

And then we need to round it up to 30.

So it's the same number of decimal places as the original readings.

So well done if you got that correct.

So let's do a question based on that learning so far.

So which of those results do you think is anomalous? Is it A, B, C, or D? Pause the video here, answer the question and I'll see you when you're finished.

So the answer is C.

You can see that is significantly different to 22.

8 and 22.

7.

So that's the anomaly, the anomalous result.

Well done if you got that correct.

Now, the uncertainty is the interval within which the true value of a measurement can be expected to lie.

And we're going to have a go at calculating uncertainty.

So uncertainty is plus or minus half of the range.

Now, the range is the highest value minus the lowest value.

So uncertainty is plus or minus half of the range.

So it's calculated by carrying out the following calculation.

So we work out what the range is and then we divide it by two.

So here's an example.

So we've got three different values here, 26.

3, 25.

9, and 27.

1.

So the first thing we need to do is work out which of those values is the highest, that's 27.

1, and then which one is the lowest, 25.

9.

And we can find the range.

So that's the difference between the two.

So we put that in brackets, 27.

1 minus 25.

9, and then the range, we need to divide by two.

And then that gives us a value of 0.

6.

And then we put plus or minus 0.

6 next to our answer.

So the higher the uncertainty, the more varied the data is.

So it shows us there's a big range between the values.

So the higher the uncertainty, the larger the range between the values that we've recorded.

Now we're going to carry out some calculations together.

So we're going to calculate the mean and uncertainty for those following masses.

And then when I've shown you how to do it, you are going to carry out the calculation for the temperatures by yourself.

If we look at those three values, we've got 31.

7, 30.

2, and 33.

5, we're going to calculate the mean and the uncertainty for those values.

So to calculate the mean, remember, we need to add the three together and divide by how many we've got.

All of those values added together, and we've divided by three because there are three masses, and that gives us a mean of 31.

8.

Now, to work out the uncertainty, we need to find the range, first of all.

So that's the highest number minus the lowest number.

So the highest number there is 33.

5, and the lowest is 30.

2.

And then we need to divide that value by two, and that gives us an uncertainty of 1.

65 grammes.

So what we can say at the end is our measured value is 31.

8 grammes, plus or minus 1.

65 grammes.

So we write down the mean, followed by the uncertainty.

So pause the video here and have a go at the second calculation.

So again, for the second calculation, we need to calculate the mean, first of all.

So that's all of those values added together and divided by three, and that gives a value of 19.

6.

And then for the uncertainty, we need the range.

So the highest value there is 20.

6, the lowest is 18.

5, and then we divide it by two.

And that gives us a value of plus or minus 1.

05.

And then we write that out as the mean plus or minus the uncertainty.

So well done if got that correct.

Now, the type of graph depends on the type of data collected.

So continuous data are numerical, such as time and temperature.

And we'll record these on a line graph where we'll plot the data on a graph and then draw a line of best fit through it.

The independent variable generally goes on the x-axis and the dependent variable on the y-axis.

There are some exceptions, but in most cases that's correct.

And continuous data are always shown using a line graph.

So we plot the points on the graph and then we draw a line of best fit, which best fits those plotted points and shows the trend or the pattern in the data.

When writing a conclusion, we need to consider the following.

A summary of the results observed, an assessment as to whether the hypothesis was correct or not, and the results observed need to be explained.

Finally, the conduct of the investigation needs to be evaluated.

So how could we improve the experiment? Do we need to use different equipment? Do we need to change the method? How would we improve the reliability of the data? Did we get any anomalous results? Did we need to repeat the experiment and take a mean of the results? We are now gonna have a go at task C.

So using the data below, calculate the mean and the uncertainty for each volume of sodium hydroxide and remember to identify and omit any anomalous results.

So circle any anomalous results in the data, first of all, and don't use those in your calculations.

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

So let's go through the answers then.

Here are the answers.

And remember that these two here are anomalous results.

So they've been omitted from the calculations.

So if your results are slightly different to mine, that might be why.

So pause the video here, check through your answers and see if you got them correct.

Now for B, we're gonna plot a line graph of the data and include a line of best fit to show the trends in the data, and then use your line of best fit to show where the solution was neutralised, so where the reaction was complete.

So you'll have two lines of best fit on the graph, and you need to show where that reaction had completed.

So pause the video here, plot a graph of that data.

Welcome back.

So hopefully your graph looked a little something like this.

It can be a little bit overwhelming to see this diagram.

So I'm gonna talk you through it.

So you should have two lines of best fit, one where the temperature is increasing and one where the temperature is decreasing.

Then the reaction's complete where those two lines of best fit cross.

And then you need to go down to the bottom to find the volume of sodium hydroxide needed to neutralise the acid.

So well done if you've ended up with a graph and it looks like that.

Now onto Question 2, we're gonna write a conclusion from your findings.

So what happened to the temperature of the neutralisation solution during the practical? Did your findings match your hypothesis? And why did you see these trends in temperature during the experiment? So pause the video now and answer those questions.

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

So 2a, first of all.

What happened to the temperature of the neutralisation solution during the practical? So the mean temperature of the neutralisation solution increased from 24.

9 to 51.

1 degrees Celsius when up to 50 centimetre cubed of sodium hydroxide was added.

After this, the temperature decreased from 51.

1 to 27.

5 degrees Celsius when up to a further 30 centimetre cubed of sodium hydroxide was added.

So there was 80 centimetre cubed added in total.

So notice the answer has got lots of figures there from the graph to explain what's happening.

Now let's go through b.

So did your findings match your hypothesis? So yes, when up to 50 centimetre cubed sodium hydroxide was added, the temperature increased.

So that agreed with our hypothesis.

However, further addition of sodium hydroxide caused the temperature to decrease.

And we didn't have that in our hypothesis.

So we just pointed that out here.

Well done if you got that correct.

Now for C, why did you see these trends in temperature? So we need an explanation now.

So the initial increase in temperature was due to the neutralisation reaction between sodium hydroxide and hydrochloric acid.

It was exothermic and released energy to the surroundings.

So we know it was exothermic 'cause the temperature increased, the reaction was complete once all of the hydrochloric acid had reacted.

And then the addition of excess sodium hydroxide cooled the reaction mixture and caused a decrease in temperature.

The exact volume of sodium hydroxide needed to neutralise the hydrochloric acid was shown where the lines are best fit crossed on the graph and was 50 centimetre cubed.

So well done if you managed to get all three parts of that explanation.

Question 3, we are now going to write an evaluation to say how we could have improved our investigation.

So we're gonna look at a, b, c, and d.

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

So let's go through the answers.

So could you have improved your equipment by further insulating the cup and using a better fitting lid to prevent heat loss? So if you've said anything about preventing heat loss by adding additional insulation, then that's correct.

By using a temperature probe to record the temperature to prevent misreading of the thermometer.

So temperature probe, remember, is easier to use than a thermometer.

Could you have improved your method? So some suggestions include thoroughly stirring the mixture after the addition of each volume of sodium hydroxide for the same number of times.

So you may have stirred the mixture from different number of times.

Now let's take a look at part c and d.

So did you obtain any anomalous results? Yes, these results were omitted from the calculation of the mean and how could you have improved the reliability of your results? So in terms of reliability, if we compared them with other groups in the class or use the data from other groups in the class, that would improve the reliability because we would be making our data more reproducible, which is quite an important thing to do.

So well done if you've got that correct.

Here's a summary of today's lesson.

Neutralisation reactions involve an acid reacting with a base to form a salt and water.

Exothermic reactions release energy to the surroundings through heating.

The initial and highest temperature of a reaction mixture need to be recorded to calculate an energy change.

Methods must be detailed and replicable for reliable data collection.

And line graphs can illustrate relationships between continuous variables in experiments.

So thank you very much for joining me for today's lesson.