Page 92 - ICSE Chemistry 6

Quick Review

• Water is essen al for life.
• The major sources of water are rainwater, surface water and groundwater.
• Water exists in three states—solid, liquid and gas. These three states of water can be interchanged
into each other by changing temperature.
• Water is an integral component of all living bodies. It is also needed for various other purposes.
• The density of water is maximum at 4°C
• Water is known as the universal solvent as it can dissolve a large number of substances in it.
• The forma on of a solu on depends on s rring, par cle size of the solute and temperature.
• On the basis of the ability of solu ons to dissolve the solute, there are three types of solu ons—
saturated solu on, unsaturated solu on and supersaturated solu on.
• Potable water should be colourless, odourless and transparent. It should have suffi cient amount of
dissolved salts and oxygen in it and should be free from harmful chemicals and microorganisms.
• Consump on of water contaminated with industrial and agricultural wastes, and human and animal
faeces may lead to various waterborne diseases.
• Purifi ca on of water involves processes of removing impuri es from water such as harmful bacteria,
dissolved and undissolved solid substances like par cles of mud, sand, grit and dead organisms.
• Some commonly used methods to purify water are sedimenta on and decanta on, loading,
fi ltra on, boiling, chlorina on, water purifi ers and RO system, aera on, ozoniza on and dis lla on.
• Water is a precious natural resource and hence we must conserve it.
• The major causes of water pollu on are discharge of domes c sewage and dumping of garbage,
industrial and agricultural wastes, waste from nuclear and thermal power plants, defeca on, and oil
spill and leakage.
• Water pollu on can be prevented by installing water treatment plants in industrial areas; by
not releasing untreated sewage, agricultural and industrial wastes into water bodies; by using
environment-friendly household products, etc.
• Flood is caused when it rains heavily or con nuously for a number of days. It leads to condi ons such
as loss of property, death of animals and humans, extensive damage to crops, soil erosion, rise in the
level of water in dams, rivers, etc. and spread of diseases and pollu on.
• Drought is a period of abnormally low rainfall, leading to shortage of water. It leads to condi ons
such as lack of food and drinking water, lower groundwater level in lakes, rivers, etc., soil erosion, loss
of plants and trees, death of animals, loss of human lives and health problems due to poor quality of
water.

EXERCISES

BE PROMPT

A. Fill in the blanks.
1. About ____________ of the fresh water is present in rivers, lakes, springs, ponds, etc.

2. In ____________ state, water exists as snow or frost.
3. Water exists as _______________ or ____________ in gaseous state.
4. The density of water is ____________ at 4 degree Celsius.

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