Question 1 State few properties of Nitrogen?
Question 2 State few properties of oxygen?
Question 3 Why do mountaineers carry oxygen cylinders with them while climbing high mountains?
Question 4 How will you show that oxygen or air is necessary for burning?
Question 5 Explain why, if the clothes of a person catches fire accidentally, he is covered with a woollen blanket? Give answer?
Question 6 Why do sea divers carry oxygen cylinders with them?
Also Read NCERT Solutions for Chapter 15 Air Around Us
Contents
Nitrogen
(1) Nitrogen is a colourless, tasteless and odourless gas.
(2) Nitrogen gas is slightly soluble in water.
(3) Nitrogen gas is not essential for breathing (or respiration).
(4) Nitrogen gas neither burns itself nor supports the process of burning.
(5) Nitrogen is a very unreactive gas.
(6) All the living things need nitrogen compounds for their growth. The plants use nitrogen gas of the air to make proteins.
(7) These proteins are used by the plants for their own growth as well as for the growth of human beings and other animals.
Oxygen
(1) Oxygen is a colourless, tasteless and odourless gas.
(2) Oxygen gas is slightly soluble in water.
(3) Oxygen gas is essential for breathing (or respiration).
(4) All the living things need oxygen of air for breathing.
(5) Oxygen gas does not burn itself but it allows other things to burn in it. So, oxygen is a supporter of burning (or supporter of combustion).Thus, oxygen supports life and combustion.
Oxygen is necessary for living things
We can also say that oxygen is necessary for breathing. All the living things (animals and plants) use the oxygen of air for respiration. During respiration, oxygen breaks down food to give carbon dioxide, water and energy.
The animals and plants living on land take the oxygen required for breathing from the air around them. But the animals and plants living in water take the oxygen required for breathing from the air dissolved in water.
Under special situations, oxygen gas cylinders are used for breathing purposes.
Three such special situations areas are patient having breathing difficulties, a mountaineer climbing a high mountain and a diver going into deep sea.
The patients suffering from diseases like asthma, etc., have sometimes difficulty in breathing properly in air because only one fifth part of air is oxygen. A patient undergoing a major surgical operation also has difficulty in breathing properly in the surrounding air. So, oxygen gas is given to patients in hospitals who have difficulty in breathing properly. All the hospitals have cylinders filled with oxygen gas for such patients.
The persons who climb high mountains are called mountaineers. The mountaineers carry oxygen gas cylinders with them while climbing high mountains. At high altitude of mountains, the air is very thin. So, the air at high altitudes contains very little oxygen due to which it becomes difficult to breathe properly. The mountaineers use the oxygen gas contained in cylinders for breathing properly under conditions of high altitudes.
When the divers go deep into sea-water, they carry oxygen gas cylinders with them. This oxygen gas is used by divers for breathing while they are under water. This is because there is no free oxygen in the sea-water which can be used by the divers for breathing. he little dissolved oxygen present in sea-water cannot be used for breathing by human beings such as a diver.
Oxygen is Necessary for Burning (or Combustion)
The process of burning of a substance is called combustion. Air is known as a supporter of combustion. When a substance burns in air, it is actually the oxygen present in air which is used up in the process of burning. The substances which are burning need a supply of fresh air all the time. This is because fresh air is rich in oxygen.
Activity : Air (or oxygen) is necessary for the burning (combustion) of things
We take a candle and fix it on a table. The candle is lighted by using a burning matchstick. The candle will continue to burn because fresh air is continuously available to the candle for its burning process. The fresh air supplies sufficient oxygen necessary for the continuous burning of the candle.
Cover the burning candle by putting an inverted gas jar over it. After a short time, the candle stops burning, it gets extinguished. When the burning candle is covered with a gas jar, then the candle takes the oxygen necessary for burning from the air enclosed in the gas jar. Since only a small amount of air is present inside the gas jar, all its oxygen is used up in a short time. And when all the oxygen of air inside the gas jar is used up, then the burning candle gets extinguished.
We conclude that air is necessary for burning of things. In fact, the process of burning cannot continue without a continuous supply of air (or oxygen).
For burning a substance continuously so as to make fire, a continuous supply of fresh air is needed (to provide sufficient oxygen for the burning process). If we cut off the supply of fresh air to a burning substance, then the burning substance will not get oxygen necessary for burning to continue and hence the substance will stop burning.
If the clothes of a person catch fire (while working in the kitchen, etc.), a woollen blanket is put around the burning clothes to extinguish the fire. Actually, when the burning clothes of a person are covered with a woollen blanket, then the supply of fresh air (or oxygen) to the burning clothes is cut off and hence the clothes stop burning (or the fire gets extinguished).
| Notes for Chapter 15 Air Around Us |
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