Hi, I'm Mrs. Hudson, and today we're going to be looking at a lesson called Heating curves: practical.

This is a chemistry lesson and it comes under the chemistry unit titled States of matter.

So let's get going.

The outcome of today's lesson is: I can record data in an accurate manner and represent it appropriately, and we're going to be looking at heating curves and how to do a practical to measure a heating curve for a specific substance.

During today's lesson, there will be three phrases and keywords that are used frequently throughout the lesson.

And these are: independent variable, dependent variable, and control variables.

So let's look a little bit closer at what each of those words mean.

Independent variable is the single variable that is changed in an investigation.

The dependent variable is the single variable that is measured or observed in an investigation.

And finally, the control variables are all variables, other than the independent and dependent variables, that are kept the same in an investigation.

And every time a scientist performs an investigation, they will have an independent variable, a dependent variable, and control variables.

Today's lesson will be split up into two parts.

In the first part of the lesson, we're going to be collecting heating curve data.

And then in the second part of the lesson, we're going to have analysis of heating curve data.

But let's get going first of all with collecting heating curve data.

This is a heating curve that can be used to determine the melting and boiling point of a substance.

So when we're producing a heating curve, you always have a graph that has time in seconds on the x-axis and temperature in degrees Celsius on the y-axis.

And when you're producing a heating curve, you have a substance which you are heating up, and then you are measuring the temperature of that substance at regular time intervals.

And you will usually end up with a graph that has a similar shape to this, and it's showing you the different states that that substance is going through.

So as you increase the temperature, then you go from a solid state, into the liquid state, and then to the gas state.

And the horizontal sections on the graph are showing you the actual change of state.

And at that point, there is no increase in temperature of the substance because the energy is being used to overcome the forces of attraction.

We can extrapolate across from the horizontal section representing the melting.

And if we go to the y-axis, it will give us the specific melting point of that substance.

And the same thing can be said for the boiling point.

So if you extrapolate across from the horizontal section where boiling is occurring and then we measure off the temperature, that will give us the specific boiling point for that substance.

To collect data for a heating curve experiment, you need a thermometer which is placed in the substance that you're measuring the heating curve of.

The substance is then heated and the temperature is recorded at regular intervals.

And we can see a labelled diagram there showing you a boiling tube which has the substance inside, which is labelled, and then the thermometer is inside of the boiling tube and inserted into the substance so that you can measure the temperature at regular intervals.

Now, there are different ways that we can measure the temperature, and there are different advantages and disadvantages to different pieces of equipment.

The temperature can be measured using a thermometer or a temperature probe.

So let's look at the advantages and disadvantages of each of those pieces of equipment.

So if we're looking at a thermometer, the advantages are that it is cheap and easy to use, but the disadvantages are that the glass is fragile, so it could be broken.

And also it can be quite easy to misread the temperature.

You are relying on somebody who is actually looking at the thermometer and reading it, and mistakes could be made there.

So if we look now at a temperature probe, which looks like this.

So you have a probe which is connected or inserted into the substance, and then you will get a digital temperature which is displayed on a screen.

Now, the advantages of this are that it's easy to read and record that data, and there is also a greater accuracy in comparison to a thermometer because you are not relying on a human who could misread the temperature.

But the disadvantages are that it's more expensive and it may be difficult to set up and use.

So in a classroom it might be that it's too expensive to use a temperature probe or potentially that to set it up is actually more difficult than setting up a thermometer.

A data logger in combination with a digital temperature probe can be used to record the temperature of a substance over time.

And we can see here that you've got an image which is showing you a temperature probe inserted into a substance, and then that temperature probe is used in combination with a data logger.

Now, data loggers are really good because they can record continuous data.

They also remove human errors, such as reading the thermometer off incorrectly.

They have a higher accuracy, and they can automatically plot a heating curve graph, which will give you brilliant results.

Let's quickly check our understanding of that so far.

Which of the following pieces of equipment will allow the most accurate data to be recorded from a heating curve experiment? A, a temperature probe; B, a thermometer; or C, a temperature probe linked to a data logger.

This is C.

The most accurate form of equipment is the temperature probe linked to the data logger.

Remember that the data logger can take continuous recordings of temperature.

Why is it better to use a data logger connected to a temperature probe than a thermometer and results table? You may select more than one answer.

A, enables readings to be taken continuously; B, takes less data points than using a thermometer; or C, draws a heating curve automatically.

This is A, enables readings to be taken continuously, and C, draws a heating curve automatically.

If you use a data logger connected to a temperature probe, it doesn't take less data points.

It continuously takes data points.

Fantastic job if you've got those right.

Well done.

We're ready now to move on to task A of the lesson.

So in the first part of task A, you need to heat a pure substance, for example, stearic acid, and then you're going to take the temperature of stearic acid at regular intervals.

And there's a table here which has been drawn for you to help guide you in your recording of the data.

So you've got the time in seconds in the left-hand column and the temperature of the substance in degrees Celsius in the right-hand column.

And then you are going to plot a graph of your data.

Now, make sure when you're plotting your graph that you're using a pencil and graph paper and that you label your axes.

Now a hint here is that the independent variable, which is the thing that you are changing each time in the experiment, that always goes on the x-axis, and the dependent variable always goes on the y-axis.

And in a table, the dependent variable is always the second column over, so in this case, the temperature of the substance, and the independent variable is always the first column, which is the time.

So your time needs to be on the x-axis, it's the independent variable.

And the temperature needs to be on the y-axis, which is the dependent variable.

I'm sure you're gonna do a really great job of this.

Pause the video, and then press play ready for me to go through the answers.

Let's see how we did.

Now, depending on what substance you've used, your graph might look slightly different to this.

And particularly when you're using stearic acid, then your graph should look like this.

So the time is in seconds on the x-axis and the temperature is in degrees Celsius on the y-axis.

And then what we should see is a slope going upwards to begin with.

And then around about sort of 70 degrees, 71 degrees, you should have a horizontal line going across, which is showing you melting.

And then it should go back up again and start to increase in temperature.

So fantastic job if you have a graph that looks like that.

Do make sure you've got the units on your axes as well.

Great job so far.

We've done collecting heating curve data, so let's move on now to look at analysis of heating curve data.

This image here has shown you the heating curve for stearic acid, which if you have done the first part of this task and you used stearic acid as a substance, yours should look similar to this.

If you've used a different substance, that's fine, but the temperature might just be slightly different at which the substance melted.

Now, really important again to remind us that in this investigation the independent variable is time, and on the graph that is represented on the x-axis, and the dependent variable is temperature in degrees Celsius, which is represented on the y-axis.

Now, the melting point of stearic acid can be determined from the graph.

And to do this, you have to find the horizontal section, which is representing melting, and then with a ruler extrapolate that line across so that it meets the y-axis.

And it's really important here that you do use a ruler to make sure that your line is completely level until it touches the y-axis.

And then you can read off the temperature on the y-axis, and that will give you the melting point of that substance.

So we can see for this graph here that the melting point sits just a little bit above 70 degrees Celsius.

Let's check our understanding.

For a heating curve investigation, which variable should you record in the right-hand column of the table? And we've got a table here with time in seconds on the left-hand column, and the right-hand column is blank.

So what would you put in that right-hand column? A, rate of heating in degrees Celsius per second; B, temperature of substance in degrees Celsius; or C, temperature of water bath in degrees Celsius.

This is B.

We are measuring the temperature of the substance in degrees Celsius, which is the dependent variable.

Fantastic job if you got that right.

Well done.

Next question is true or false.

When drawing a heating curve, time is plotted on the x-axis.

True or false? And then justify your answer: A, time is the dependent variable in this investigation, or B, time is the independent variable in this investigation.

So when drawing a heating curve, time is plotted on the x-axis.

This is true.

And the justification is B, time is the independent variable in this investigation, and the independent variable is always on the x-axis.

So well done if you remembered that.

To improve the reliability of your data, you can repeat the experiment at least three times.

And if you repeat the experiment, this helps us to identify the second point, which is to remove anomalous results, ones that do not fit the pattern of the rest of the results.

So if you repeat the experiment, you have multiple versions of the results and that allows us to identify anomalous results and then remove them.

And also, you want to calculate a mean for each data point.

So if you have repeated the experiment, you'll have multiple data sets, and therefore you can calculate a mean once you have removed anomalous results.

To calculate the mean, you have to add up each individual value and then divide by the number of values that you have.

A quick question on that: what is an anomalous result? A, the biggest value; B, a value that does not fit the pattern of the results; or C, the mean value.

An anomalous result is B, a value that does not fit the pattern of the results.

So well done if you got that right.

Another check for understanding here.

Identify the anomalous result in the table.

Now we are looking at the circled results, A, B, and C.

So you have to check if they correspond and match up with the results within the same time.

So which one of those results are anomalous? This is B.

So you can see that for 120 seconds, the first test had 31 seconds, the second test had 42.

6, and the third test had 32.

2.

So 42.

6 is a very different result to 31 and 32, so we would say that that result is anomalous.

Whereas if we look at time 0, 26 is a little bit higher than 25.

2, but it's not really different.

And the same for 240 seconds.

41 is a little bit higher than 40.

6 and 38.

8, but it's not a lot higher in the same way that 42.

6 is in comparison to 31 and 32.

So you would have to remove result 42.

6 from test 2 in 120 seconds.

Really great job if you got that right.

Well done.

Next question now is, can you calculate the mean temperature of salol at 360 seconds? So you've been given test 1, test 2, and test 3 results.

So you need to calculate a mean for that data set at 360 seconds.

So to work this out, you needed to do 71.

8 plus 71.

6 plus 72, and then you would've had to have divided that answer by 3, which is the number of results that you've got.

And the answer you should have got is 71.

8.

So great job if you got that right.

Well done.

And then another question here.

Which of the following would not improve the reliability of your results? A, repeating the readings at least three times; B, removing any anomalous values before calculating a mean; or C, taking your data readings less frequently.

So this is C.

Both A and B would actually improve the reliability of your results.

So repeating readings three times and removing anomalous results before calculating a mean, those were things we said actually improve the reliability of your results.

And taking more data readings is a good way to improve reliability.

By taking data readings less frequently, you will actually be decreasing the reliability of your results.

So great job if you've got those right.

Well done.

We're ready now to move on to task B.

And in the first part of task B, you need to use your heating curve from task A to determine the melting point for stearic acid.

Then number two, suggest how you could improve the reliability of your data.

I'm sure you're gonna do a really great job of this.

Pause the video, give it your best go, and then press play when you're ready for me to feedback on the answers.

Let's see how we did.

So in the first part, we needed to use our graph from task A in the lesson.

And to get the melting point, you would need to extrapolate across from the horizontal section that represents the melting point on your graph.

And I said to use a ruler to do this.

So we'd use a ruler to draw a line across that intersects your y-axis, and we can see that from this graph it's roughly around about 69 degrees Celsius.

And your results should roughly be between 69 to 71 degrees Celsius for stearic acid.

So really great job if that's the answer that you got.

And then number two, suggest how you could improve the reliability of your results.

You would need to repeat the experiment to get at least three sets of results.

You would then remove anomalous values, the ones that do not fit the data pattern, and then you would take a mean for each data point.

Fantastic job if you remembered all three of those things that we can do to improve the reliability of results.

If you want to pause the video to go back and look at the answers in more detail to add anything in and correct yours, then please do.

But on the next slide, we're going to summarise everything that we've learned this lesson.

Today, we've been looking at heating curves and the practical element of how we perform heating curves and the analysis of them.

And we said that to plot a heating curve, the temperature of the substance can be recorded at regular intervals as it is continuously heated.

And we did talk about a few ways that we could measure the temperature with a thermometer, with a temperature probe, or with a temperature probe connected to a data logger.

And we said that a data logger connected to a temperature probe was the most accurate way to collect data because it continuously takes temperature recordings and then will draw a heating curve for you.

We then said that these observations can be recorded in a table and represented graphically by plotting a trend line.

And then taking repeat measurements, removing any anomalies, and calculating averages improve the reliability of that data.

And then finally, we said that the melting point of a substance can be determined from the heating curve.

And to do that, you extrapolate across from the horizontal section that represents melting until it intersects your y-axis and then you read off the temperature on the y-axis.

And really important to always use a ruler when you are doing that.

I've really enjoyed today's lesson, I hope you have too.

And I look forward to seeing you next time.