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Melting Points & Boiling Points
Objectives
To see how different solids can become liquid when heat is applied.
To understand that different solids take different lengths of time to melt into a liquid state.
Resources
Cambridge Primary Science Book 4 | Lined paper | Ice cube | Butter | Chocolate | Hot plate and pan | Digital timer | Long thermometer
Today's Lesson
Main Activity
Turn to page 62 in Cambridge Primary Science Book 4and read the text together.
Watch the Changes of State and Temperature video.
Discuss how different metals melt at different temperatures.
Then ask your child to think of some reasons that people might have for wanting to melt various metals. For example, gold and silver for ornamentation and jewellery, iron for industry and horse shoes, brass for ornaments.
Ask your child to make a list of different objects around your house that are made from metal and to try to identify the metal involved. Then ask them to access the internet to find the melting point of that metal.
They should create a list of various metals, their uses and melting points, that they can continue to add their discoveries to as they continue with their learning.
It is unlikely that you have a mercury thermometer at home to look at, but you can access a picture of one online to observe the liquid metal inside. Explain to your child that mercury (sometimes known as quicksilver, whose chemical symbol, Hg, comes from the Latin word hydrargyrum, meaning ‘watery silver’) is the only metal that exists in the liquid state at room temperature (around 20 degrees Celsius).
All substances melt at different rates because they require different amounts of heat (temperature). The temperature at which a substance melts is its melting point.
It is important to note that not all substances melt when heated. Wood, for example, burns, preventing it from becoming a liquid.
Similarly, all substances boil at different rates. The temperature at which a substance boils is its boiling point.
Temperature is measured with a thermometer. The normal room temperature for water is 20 degrees Celsius.
Now you are going to conduct an experiment on melting and boiling points of water whilst your child watches and takes notes of the experiment.
Place ice cubes in a pan and heat them. Once melted, remove them from the heat and take the temperature of the water. Take care when measuring the temperatures to ensure that the thermometer does not touch the side or bottom of the pan. Using tongs, hold the thermometer in the liquid, taking care to keep your hands away from the steam. This is the melting point.
Return the pan to the heat until it boils. At this point, record the temperature, this is the boiling point.
Ensure your child has a good understanding of the concepts introduced:
The melting point of water is 0°C and the boiling point is 100°C. The boiling point is the temperature at which a substance changes from a liquid to a gas. The melting point is the temperature at which a substance changes from a solid to a liquid.