3.4 Boiling point and melting point

• Natuurkunde / Scheikunde
• Middelbare school
• havo, vwo
• Leerjaar 2

Chapter 3.4 Boiling point and melting point

Schedule for this lesson

Explanation about the new paragraph

Making question in the workbook

Learning objectives 1/2

-You can describe what happens when water boils

-You can describe what the boiling point and melting point (freezing point/solidification point) of a substance are

-You can explain why the boiling point and the melting point are properties of a substance

Learning objectives 2/2

-You can explain how you can lower the freezing point or melting point of water

-You can interpret the melting, freezing and boiling graphs of a substance in a temperature-time diagram

The boiling point

If we heat up water, bubbles start to appear and disapear

These bubbles consist of air, and in later stages of water vapour

The boiling point

When the temperature has reached 100 degrees Celsius, the bubbles consisting of water vapour reach the surface.

At the surface they pop and the water vapour mixes with the air above the water

The boiling point

This proces is called boiling, water not only evaporates at the surface of the water, but throughout the whole liquid.

If we keep heating it, the water

continues to boil until it has all

evaporated.

The boiling point

Last lesson you did an experiment where you measured the temperature of water over time while heating it up. 

What was the highest temperature you have measured?

• 100 degrees Celsius, this is the boiling point of water, it is a point because it is fixed

The boiling point

The boiling point is a property of a substance

The melting point and freezing point

We can turn water into ice by putting it in a freezer. 

The temperature of the water has to remain at 0 degrees celsius.

And when we take out the ice cubes, they won't melt instantly either.

The melting point and freezing point

Ice melts at the same temperature  as freezing water, 0 degrees Celsius

This temperature is know as the melting point and freezing point of water

Other substances have their own melting point

The boiling point

Iron has a melting point of 1559 degrees Celsius!

Lowering the melting or freezing point

We are able to lower the freezing point of water by adding a different substance

Examples are antifreeze and salt

Melting and solidification diagrams

Making questions 3.4

Do the following questions: 1, 2, 3, 4, 6, 8, 9 and 10

Done? Finish up your poster and add paragraph 4

End of the lesson