Lesson video

Hello, my name is Mrs. Mehrin, and I am so excited to be learning all about melting temperatures, and we are going to be doing some research today.

Let's begin.

Hello and welcome to today's lesson from the unit Introduction to States of Matter and Changing States.

Your learning outcome is I can research and compare the melting temperatures of common materials.

Now, I know that learning can sometimes be a little bit challenging, but that's okay because it just means that we are going to work really hard together and we're going to learn some fabulous new things.

Let's begin.

So here are all of your keywords for today's lesson.

Now I am going to be referring to these keywords throughout today's lesson.

However, if you find it helpful, you can pause the video here, and you can jot these down now.

Off you go.

Fantastic, well done.

So, your lesson is split into two parts today.

Let's begin with the first part, measuring melting temperatures.

So, Lucas and Sam have been investigating the melting temperatures of different materials.

I want you to explain to a partner what the melting temperature of a material is.

What does it mean? Just give it a go.

Don't worry if you're not sure.

I just want you to have a try.

So, I'm going to give you five seconds now to do that.

However, if you find that you need a little bit more time, that's okay.

You can pop the video on pause here, and you can have a go at doing that.

Off you go.

Fantastic, well done.

So, the melting temperature of a material is the temperature at which it turns from solid, from a solid state to a liquid state.

And the temperature is measured in degrees celsius, which is often abbreviated to this symbol here, which is a small circle in the left top corner and then a C.

So, Lucas asks the question, why is it useful to know the melting temperatures of materials? Do you have any ideas? I'll give you five seconds to think about your answer.

Off you go.

Fantastic, well done.

So, knowing the melting temperatures of materials is important for scientists and engineers.

And scientists and engineers select materials for particular jobs based on their properties.

So, for example, when making tools or cooking utensils that will get hot, materials need to be chosen that aren't going to melt.

Because if you choose something that gets hot and then begins to melt, you no longer will be able to use that tool or that cooking equipment, for example.

Now understanding melting temperatures can help scientists identify unknown substances.

Now Lucas has a material which is made of solid white crystals, and he would like to know whether or not it's salt or sugar.

And Lucas says, I could find out whether it is salt or sugar by finding out its melting temperature.

Well, that's very interesting.

Now Sam says, I don't think that would help because all materials have the same melting temperatures.

Do you agree with Sam? Do you think all materials melt at the same temperature? I'll give you five seconds to think about your answer.

Off you go.

Fantastic, well done.

Well, different materials have different melting temperatures.

Is that what you said? So, all materials will have a different melting temperature.

They are not all the same.

And sugar and salt, even though they look very, very similar to each other and you would could easily mix them both up if you weren't to taste it, if you were just to look at it, they have different melting temperatures.

So, the melting temperature of sugar is much lower than the melting temperature of salt.

So, sugar melts at 186 degrees celsius.

Remember that symbol that we talked about where you've got that small circle and the C, and it means celsius.

And salt melts at a whopping 806 degrees celsius.

That is absolutely unbelievable.

And Lucas says, wow, those melting temperatures are very high.

No wonder I have never seen sugar or salt melt, and neither have I.

Now let's do a quick check in of your learning.

It says, what is the melting temperature of a material? Is it A, the temperature at which it changes from a gas state to a liquid state, B, the temperature at which it changes from a liquid state to a solid state, or C, the temperature at which it changes from a solid state to a liquid state? I'll give you five seconds to think about your answer.

Off you go.

Fantastic.

Well done.

The answer is C, the temperature at which it changes from a solid state to a liquid state.

Now, Lucas says, I think you can tell whether something is likely to have a high or low melting temperature by looking at it.

And he says, I think butter has quite a low melting temperature because I saw butter melt when I left it out of the fridge.

And here is a picture of the solid state of butter.

Now, Sam says, I know that ice melts at zero degrees celsius.

So, I think butter has a slightly higher melting temperature.

I predict the melting temperature of butter is approximately, so roughly 20 degrees celsius.

Now you can make predictions about melting temperatures just like Sam has.

Now let's do a quick check-in of your learning before we continue.

So true or false, different materials have different melting temperatures.

Is that true or false? I'll give you five seconds to think about your answer.

Off you go.

Fantastic.

Well done.

The answer is true.

And that's because the melting temperature of a material is a property.

And as with other properties, this varies between materials.

Different materials change from solid states to liquid states at different temperatures.

Now we are on to the first task of your learning today.

And it says, for each of the materials in the table, predict what you think melting temperature would be.

And then I want you to leave an empty column at the end.

So, I'd like you to pause the video now and have a go at doing this.

Think about what you know about these materials.

Have you ever seen it melt before? What predictions could you make? And think really carefully about them.

Don't just pop any number down.

Really think hard about it.

Okay, I'll give you some time now.

So, pop the video on pause.

Off you go.

Fantastic.

Well done.

So, you might have got something very similar to this.

So, butter, 20 degrees celsius.

Cheddar cheese, 30 degrees celsius.

Ice, zero degrees celsius.

Kitchen foil, which is aluminium, 150 degrees celsius.

Candle wax, 60 degrees celsius.

And chocolate at 25 degrees celsius.

Now we are on to the second part of our learning today, which is how scientists find melting temperatures.

So, Lucas and Sam are thinking about the investigation they did using bowls of different temperature water to help them work out the melting temperatures of different materials.

And here is a picture of Lucas and Sam's investigation.

Lucas says it was very difficult to take an accurate measurement of a material's melting temperature.

And that's because it's not always easy to find out the melting temperatures of different materials.

Scientists must make accurate observations to decide when something begins to change from the solid state to the liquid state.

And it's often hard for them to create temperatures high enough to make some materials melt.

So, Sam says, well, how could we find out whether our predictions are correct? How do scientists measure melting temperatures? Well, finding the melting temperatures of materials can present several challenges for scientists.

Some materials, such as most metals, have really high melting temperatures.

And it's difficult for scientists to create these temperatures safely, as they need to use containers, and equipment which have higher melting temperatures than the substance being tested.

Because although this does look like, although we have this container, which is metal, it'll be a different type of metal where they are melting different metals inside.

Because if it was made out of the same material, they would all melt at the same time, and you would not be able to create things that you needed to or to test any temperatures out, for example.

So, it can also be difficult because some materials change in other ways, like burning before they actually melt.

So, some materials are mixed with others, which make it difficult to work out their melting temperatures.

And scientists use a range of methods to measure the melting temperatures of materials.

So, once the melting temperature of a material has been measured by one scientist, other scientists can use this information to help them in their own work.

So, they can go and have a go at melting the temperature of a material themselves, because they can use other scientists' work to help them.

They don't need to measure it again every single time.

And melting temperatures can be researched using secondary sources of information, including books, articles, and the internet.

So, Lucas says, so can I use the internet to research the melting temperatures of different materials to see how accurate I was with my predictions? Secondary sources are texts, images, or objects created using information gathered by others.

And Lucas says, I searched online to find the melting temperature of aluminium.

Sam says, I found the melting temperature of different plastics in a science book at the library.

And when carrying out research, more than one source should be used to check that the information is accurate and reliable.

So, Lucas says, on the website I looked at, it said that the melting temperature of salt is 806 degrees celsius.

And Sam says, on the website that I read, it said the melting temperature of salt is 750 degrees celsius.

Lucas and Sam know that it's important to use more than one secondary source to be confident that their data is accurate and reliable.

So, they decide to look for a third source of information about the melting temperature of salt.

Now the reason for this is, on the internet, lots of people can put out information there.

So, some of it might be accurate, some of it may not be.

So, it's always good to check multiple sources before you make a decision.

So, let's do a quick check-in of your learning.

And it says, what do you call information which is created using information gathered by others? Is it A, a primary source, B, secondary sources, or C, tertiary sources? I'll give you five seconds to think about your answer.

Off you go.

Fantastic, well done.

The answer is secondary sources.

Now, when carrying out research using secondary sources, how many sources should be used to ensure that information is reliable? Is it A, one is enough, B, more than one, or C, as many as possible? Again, I'll give you five seconds to think about your answer.

Off you go.

Fabulous, well done.

The answer is more than one.

Now, task B.

You've got two parts to this task.

Let's start with the first part.

It says, research melting temperatures of given materials.

I want you to use more than one secondary source of information to research, and record the melting temperatures of each material in task A, and then add them to your table in the final column.

Remember, don't stick to just one.

Have a look at more than one source of information to see what the most reliable answer is.

I want you to discuss with a partner how close your prediction was to the real melting temperature, and were there any results that surprised you? So, I'm going to give you some time now.

I want you to pause the video here and have a go at doing this activity, then come back once you are ready.

Off you go.

Fantastic, well done.

So here is the actual melting temperature.

Yours might be slightly, slightly different.

It shouldn't be massively different from these.

And as you can see, I've put a range here, so it could be anywhere between these numbers.

So, for butter, anywhere between 32 to 36 degrees celsius.

For cheddar cheese, anywhere between 60 and 66 degrees celsius.

Ice is zero.

Kitchen foil, 660 degrees celsius, which was a lot more than predicted.

Candle wax, 46 to 86 degrees celsius, and chocolate 37 to 50 degrees celsius.

And with chocolate, there are so many different types of chocolate that you can have quite a big range.

Same with the candle wax as well.

So now you are on to the second part of Task B.

I want you to research melting temperatures of materials of your choice.

So, I want you to carry out research to find out the melting temperatures of five other common materials.

So, you could look for materials in the classroom, in your kitchen cupboard, the supermarket, or in the town.

I want you to make a game by drawing each material and a separate piece of card, and writing the melting temperature on the back.

Shuffle them up and ask a partner to try to place the cards in the correct order from lowest to highest melting temperature.

That sounds like a lot of fun.

So, I'd like you to pause the video here and have a go at doing that.

Off you go.

Fantastic.

Well done.

So, your results might have looked like this, but you may have had different materials that you used.

So, a crayon is 49 to 64 degrees celsius.

Olive oil is minus six degrees celsius.

Clay is 1,250 to 1,800 degrees celsius.

Marshmallow is 35 degrees celsius, and tarmac is 50 degrees celsius.

And here are the cards.

So, your cards might have looked like this.

And remember, I asked you to play this game with a partner and ask them to put things in the correct order.

So, now we are on to the summary of our learning today.

So, the melting temperature of a material is the temperature at which it changes from solid state to liquid state.

Different materials have different melting temperatures.

It's often hard for scientists to create temperatures high enough to make some materials melt.

Melting temperatures can be researched using secondary sources of information.

And when carrying out research, more than one source should be used to check that the information is accurate and reliable.

Well done for today.

You have worked absolutely brilliant.

I am so proud of your critical thinking.

Fantastic research done by you as well today.

Well done.