الأسبوع 1 · الفصل 1 «شروط الاحتراق»: 1-1 كيف تحترق الأشياء والهواء، 1-2 دور الأكسجين · 3 دروس
3
Oxygen helps fire, other gases do not
Science P6: Term 1, Chapter 1, pp. 6–11
GoalShow with a prediction which gases help burning and which do not, and say how fire extinguishers use this.
New words
burn · to react with oxygen and give out heat and lightextinguisher · a container with a substance that puts out a fireprediction · what you think will happen, before you see it
Explanation
Scientists test each gas separately. Imagine a glowing incense stick placed in a jar of oxygen: it burns brightly and fast. In a jar of nitrogen, the glowing stick goes out. In a jar of carbon dioxide, it also goes out. The result tells us that oxygen helps things burn, while nitrogen and carbon dioxide do not. Be careful with the words: oxygen is not the fuel. The fuel is the wood or wax or gas. Oxygen is the helper that lets the fuel burn. This is why a flame that cannot get fresh air weakens: it does not mean every bit of oxygen is gone, only that there is not enough for the flame to keep burning. These tests are done by adults in a laboratory or on video, and you make predictions.
Gas in the jar
Glowing stick (predict)
Why
oxygen
burns brighter
helps burning
nitrogen
goes out
does not help
carbon dioxide
goes out
does not help
Worked examples
A fire engine carries a carbon dioxide extinguisher for electrical fires. The gas pushes air away from the fire, and carbon dioxide does not help burning, so the fire goes out.
Karim says: “The flame went out, so all the oxygen was used up.” His teacher says: not all of it. Some oxygen remains, but there was not enough for the flame to keep burning.
A hospital keeps oxygen cylinders away from flames and sparks. Because oxygen helps things burn strongly, a spark near it is dangerous.
Class activity
Prediction cards. Write three cards: oxygen, nitrogen, carbon dioxide. On the back of each, write what a glowing stick would do and why. Swap with a partner and check each other’s cards. Remember: no matches or candles at home.
Practice
1
A glowing stick goes into a jar of nitrogen. Predict.
It goes out, because nitrogen does not help burning.
2
Which gas makes a glowing stick burn brighter?
Oxygen.
3
True or false: oxygen is the fuel.
False. The fuel is the wood, wax or gas. Oxygen helps the fuel burn.
4
Why is carbon dioxide used in some fire extinguishers?
It does not help burning, and it keeps air away from the fire.
