In this latest Hub Lab experiment with Phil of Science, we will learn about gasses and how they behave when they come into contact with heat.


We are going to learn about...
1. Heat
2. Gases and their composition
3. Air pressure, expansion, and contraction


For the first part, get your three long candles, each of different hights. Light them all and place a big class jar over them. (You can also do this with a smaller glass and birthday candles of different heights)

Predict what you think will happen! You should notice that the tallest candle goes out first, this is because the candles burn the oxygen in the air and produce carbon dioxide. Since the carbon dioxide produced is hot, it is less dense and therefore rises to the top of the jar. 

The tallest candle is now surrounded by carbon dioxide and goes out as it has no oxygen around it to burn. Now let's test how much air can expand and contract when it is heated and cooled.

You can set up this experiment a few ways. Stick a birthday candle in some bluetac on a plate or sit a match on a stack of coins on the plate. Pour some water onto the plate…. you can even ad a few drops of food colouring too!

Another one of Phil's classic t-shirts!

Light the match/candle and then place the glass over it. As the candle burns it heats up the air in the glass, you may notice some bubbles at the bottom as the air expands and ties to escape. When all the oxygen has been burned up, the flame goes out and the water begins to get sucked into the glass.

Why is this happening? As the air cools after the flame is extinguished, it begins to contract. This creates a lower pressure, or vacuum, inside the glass than outside and causes the water to get pushed up to the area of low pressure. The water will stop rising when the pressure is equal between the inside and outside of the glass.

Play around with this experiment. What happens if the water is warmer? What happens if we burn more than one candle? Test it out! Make sure you follow a scientific procedure and get an adult to help.

You can download all the instructions and more information here!

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