Burning Fuels

• Fuels need heat to set them alight and air (oxygen) to keep on burning.

• Teacher writes the following words on flard cards: burning fuels, energy and oxygen.
• The flash cards are used to explain what burning fuels require.
• The teacher tells the learners that burning fuels require energy from oxygen to start burning.
• Different types of gas are found in the air as follows:
  • Nitrogen – 79%.
  • Oxygen – 20%.
  • Other – 1%.
• Show Video Clip 3 (4:27 minutes).  
• Prepare the learners for the practical task that will follow.
• They are reminded to be observant so that their recordings can be accurate.
• Their attention is also drawn to safety precautions when working with matches and candles.

• This activity is a practical task that can be completed for marks.
• Divide the class into groups, however, learners should work on their own when they record information.
• Provide guidance where required, but remember they should be able to complete the activity on their own as they would have practiced it before.
• Each group conducts the experiment.
• Each group will need:
  • A candle.
  • Two glass containers of different sizes.
  • Stop watch (a cell phone can be used).
• Method:
  • Light the candle and then put the first glass container over it.
  • Measure in time how long it takes the candle’s flame to go out.
  • Repeat the experiment with the second glass container.
  • Repeat the experiment without any container over the candle.
• Learners record their findings in their (Worksheet E).
• Learners provide feedback on their findings. Review their answers and correct statements as required.
• Introduce the concept of a HYPOTHESIS: Ask learners to make a sentence using “If”…and “Then”…

• Ask the following questions:
• What does a fire need to burn?

Answer:  oxygen, fuel, source of energy

• What did we need for the candle to burn in this experiment?

Answer:  Air (oxygen) to support the burning

• Fuel (candle wax).
• Source of energy (burning match or lighter):
  • How much of the air that are around us consists of :

• Inform the learners that they will first watch a video clip about burning substances before they go to a demarcated section on the school ground to do an experiment.
• They are reminded to take note of the different substances and its effects.
• They are also informed that the burning would stop once the fuel or the oxygen has been removed.
• Introduce the Fire Triangle which requires all three sides of the triangle for combustion: Fuel; Oxygen and Heat.

• The following experiment must preferably be done on the school grounds under the strict supervision of the teacher.
• Equipment needed:
  • a piece of wood and a candle – both items must be of the same weight;
  • paraffin;
  • matches & firelighter;
  • candleholder.
• Method
  • Learners make their hypothesis whether the candle will burn out quicker or longer or at the same time as the wood.
  • One learner can be asked to place the wood on the ground.
  • The teacher pours some paraffin over the wood.
  • The teacher sets the wood alight with a firelighter.
  • One learner can hold the candle while another learner carefully lights the candle with a match at the same time when the teacher lights the wood.
  • The learners compares the learners’ hypothesis with the results of the experiment to see who was correct or the closest.
• Learners record the information on this experiment in Worksheet F.