Carbon Dioxide, Water Vapours and Smoke

Question 1 State few properties of Carbon Dioxide gas?

Question 2 From where does dust enter into the air?

Question 3 Why should we breathe through the nose and not through the mouth?

Question 4 What is smoke? How is smoke produced?

Question 5 Explain why, tall chimneys are installed in factories?

Question 6 Why do traffic policeman often wear mask at a crowded city?

Question 7 What is the importance of water vapours in air?

Question 8 State the importance of Carbon dioxide for living things?

Also Read NCERT Solutions for Chapter 15 Air Around Us

Carbon Dioxide

(1) Carbon dioxide is a colourless and odourless gas.

(2) It has a slightly sour taste.

(3) It is moderately soluble in water.

(4) It neither burns nor supports burning.

(5) It extinguishes a burning fire.

(6) Plants and animals consume oxygen from air for respiration and produce carbon dioxide.

 

If some material is burning in a closed room, we feel suffocated. This is due to the accumulation of excess of carbon dioxide (and some carbon monoxide) in the air of the room which is produced by the burning material.

Green plants need carbon dioxide gas to make food. In sunlight, green plants use carbon dioxide from air and water from soil to make food by the process of photosynthesis.

Without carbon dioxide in air there would be no plants or animals on the earth. The plants which live in water use the carbon dioxide dissolved in water for their needs.

Water Vapour

When air comes in contact with a cool surface (as that of a glass containing ice-cold water), the water vapour present in it condenses to form tiny drops of liquid water on the cold surface. Water vapour comes into the air from the evaporation of water present on the earth (in ponds, lakes, rivers and oceans, etc.) and from transpiration. It is water vapour present in air which rises high in the sky along with hot air, gets cooled, condenses to form clouds and then brings rain on the earth.

Dust particles

Dust particles are always present in air. The dust particles come into air from a number of sources such as blowing of wind, traffic on the roads, dusting at home, earth moving operations, construction activities and agricultural practices.

The presence of dust particles in air varies from time to time and place to place. We breathe in air (inhale air) through our nose. This is because fine hair and mucus are present inside the nose to prevent dust particles from entering into our respiratory system.

We should never breathe in air (or inhale air) through our mouth. This is because if we breathe through our mouth dust particles present in air may enter our respiratory system (lungs, etc.) and damage our health.

Smoke

Smoke consists of fine carbon particles and some gases.

Smoke is produced by the burning of fuels (such as wood, coal, kerosene, petrol, and diesel, etc.). Breathing in air containing smoke damages our health. The tall chimneys in factories are installed to take the smoke produced in the factory high up in the air so as to reduce its harmful effects on the ground.

This smoke is emitted into air through the exhaust pipes connected to the engines of vehicles. The traffic policemen who regulate traffic at crowded city road crossings often wear masks . The traffic policemen wear masks to protect themselves from the smoke containing harmful gases which is emitted by the vehicles moving around them.

Notes for Chapter 15 Air Around Us Composition of Air Oxygen and Nitrogen Carbon Dioxide, Water Vapours and Smoke Availability of Oxygen to Plants and Animals