Chapter No 15 Chemistry Class 10 Notes

Chapter No 15 Chemistry Class 10 Notes


Q.1: Describe the occurrence/sources of water.

Ans:  Occurrence of water:

Water is one of the most abundant natural resources present on earth. It has been estimated that the total volume of water present on earth is about 1,33 billion cubic kilometres. It covers nearly 70 per cent of the earth’s surface.

The major reservoirs of water on the earth’s surface are oceans, ice caps, glaciers, underground water, inland water, and atmospheric water.

The oceans contain more than 97percent of the total water. The rest of the water is in the form of glaciers, ice caps, underground water, inland water, and atmospheric water.

The inland water includes rivers, lakes, streams, canals, and soil moisture.

S.NoWater reservoirsAmount of water
2Glaciers and ice caps2.14%
3Underground water0.6%
4Inland water0.2%
5Atmospheric water0.001%

Although an enormous amount of water is present on earth the freshwater needed for humans is only 0.2% of the total.

Q.2. Describe the importance of water?

Importance of water:

Water is very important for us and for the whole world. After air, water is the second important agent for the survival of life. Without water, life is impossible. In the holy Quran the importance of water has been revealed as mentioned in the following verse:

Translation: And we made every living thing from water.

Some importance of water is given below:

i. Importance for life survival:

Humans can live without food for more than two months but without water, they cannot live for more than a week.

ii.  Importance for the body of humans and plants:

Human the body contains about 65-70 percent of water while plants contain 50 to 80 percent water.

iii. Importance for biological processes:

Water maintains various biological processes. The main function of protoplasm is due to the presence of a constant amount of water in it. The various reactions which occur in our body, for our existence, are due to water.

iv. Medicinal Importance:

A large number of medicines are prepared in water.

v.  Importance of transport:

Water is a good medium of transportation as ships and boats move on water.

vi. Importance as a universal solvent:

Water is a universal solvent as it can dissolve many substances in it. Due to this property water is used for various purposes like cleaning, making medicines, etc.

vi. Cooking and washing:

Cooking and washing are done in water.

vii.       As coolant:

It is used as a coolant in radiators of automobile engines. It is also used as a coolant in nuclear power plants, iron and steel industries, and other heavy industries.

viii. Agricultural importance:

A large amount of water is needed to cultivate fruits, vegetables, and other crops.

ix. Industrial importance:

Various industries require water for various purposes like textile industries, paint industries, fertilizer industries

Thus, in short, it can rightly be said that without water life is impossible.

Q.3: Write a note on maintaining water quality.

Ans: Maintaining water quality:

It is explained under the following headings:

Good quality water:

Water that supports living organisms and protects their health is good quality water.

Basis of water quality:

The quality of water is determined on the basis of its physical. chemical, biological and radiological characteristics.

Ways to maintain good quality water:

A wide range of human activities is affecting the quality of water. If this is not controlled, not only the environment will suffer but we will face numerous problems like shortage of drinking water, irrigation problems, etc.

The following are some ways to maintain good quality water.

i.  Awareness campaign:

As humans are responsible for affecting the good quality of water. Therefore, its quality can be maintained by promoting awareness among the people about water quality.

ii. Process waste materials:

Waste material must be properly processed and must not be added to water reservoirs,

III. Process sewage water:

Sewage water must not be added to water reservoirs and must be processed properly.

iv. Avoid wasting water:

Only 0.2 percent of water is available for human use. Therefore, wastage of water must be avoided. We must use water whenever needed.

Q.4: Describe the composition of water.

Ans: Composition of water:

Water is a compound of hydrogen and oxygen. However, it was considered as an element before 1776 AD. In 1776 AD, Henry Cavendish, experimentally proved that water is not an element but a compound of hydrogen and oxygen. The composition of water is given below:

Composition by volume:

Water contains two parts of hydrogen and one part of oxygen by volume. This ratio can be determined experimentally by the electrolysis of water in Hoffman’s voltmeter in the presence of an electrolyte. When an electric current is passed through acidified water it gives two parts of hydrogen and one part of oxygen.

Electrolysis of water hoffman voltameter 1



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