Lessons 5–7 · 3 lessons · K. T. Suyarov, Z. B. Sangirova, M. T. Umaraliyeva, S. G‘. Xasanova, M. K. Yuldasheva, D. T. Hasanova. Natural Science, Grade 6 (new edition). Republican Education Centre, 2022
7
Gases
Textbook, pp. 19–20
GoalExplain the properties of gases, their use in daily life and gas-safety rules.
New words
air · havonatural gas · tabiiy gazcarbon dioxide · karbonat angidridcarbon monoxide · is gazi
Explanation
Gases are colourless so we cannot see them, but we feel air when the wind blows. A gas has no shape or volume of its own and fills the whole container it is in. The distances between gas particles are large, so a gas is easy to compress: close the tip of a syringe and press the plunger and the air volume gets smaller. We breathe air; fuel also needs air to burn and many engines need it to work. Natural gas is used for heating and cooking. When it burns completely it makes water vapour and carbon dioxide; when it burns incompletely it makes carbon monoxide, which is extremely poisonous. Natural gas has no smell, so a special odour is added to it to make leaks noticeable.
Worked examples
A car airbag fills with gas in a crash and lowers the risk of the head hitting the interior. Air pushes up on a parachute so the parachutist lands slowly. A diver breathes from an air cylinder under water.
If a glass jar is put over a burning candle, the flame goes out once the air (oxygen) inside is used up. So burning needs air.
Class activity
Demonstration (teacher only): a candle in a holder is lit and covered with a glass jar; pupils time how long it burns with a stopwatch. Compare with a larger jar, where the candle burns longer. Safety: use a long match, tie back hair, pupils stand 1.5 m away, keep a bowl of water nearby; pupils never light flames themselves. If you smell gas at home: do not light a flame, do not press any electric switch, open a window, go outside and call 104.
Practice
1
State two properties of a gas.
It has no own shape or volume; it is easily compressed; it fills the whole container.
2
What forms when natural gas burns completely and incompletely?
Completely: water vapour and carbon dioxide; incompletely: carbon monoxide.
3
Why is an odour added to natural gas?
The gas is odourless; the smell lets people notice a leak at once and stay safe.
4
What should you do, and not do, if you smell gas at home?
Open a window, go outside and call 104; do not strike matches or lighters or press electric switches (risk of a spark).