Page 176 - ICSE Chemistry 8

from the sea to the coast. Since cool air is moving from the sea to the coast, it is called sea breeze.
During the night, land loses heat faster than water and becomes cooler faster. Now, the air over
the sea rises up and the cooler air over the land rushes to take its place. Therefore, during the
night wind blows from the land to the sea and is called land breeze.
day night

warm air warm air
cool land
cool sea breeze breeze

sea cooler sea warmer
land warmer land cooler

Fig. 8.7: Sea breeze and land breeze

Effects of Anomalous Expansion of Water

The survival of aqua c animals in cold regions is a ributed to anomalous expansion of water. The surface
water cools faster and gets converted into ice. This layer of ice fl oats on the surface since it is lighter in
density and acts as an insulator thereby preven ng heat loss from lower layers. Therefore, water in the
lower layers remains liquid and provides shelter to the aqua c animals. The bo om most layer of a water
body consists of water at 4°C because it is the heaviest at this temperature. Thus, aqua c life tends to
remain near the bo om where the condi ons are favourable for their survival.

Take a Break!

Write/Choose the correct answer.
1. Water helps in excre on of wastes from the body in the form of sweat and urine. (True/False)
2. Where does the water present in rivers, lakes and ponds come from?
3. Potable water is not fi t for drinking. (True/False)

4. With increase in pressure, the boiling point of water decreases. (True/False)
5. Which feature of water helps aqua c animals to survive in winters?

DISSOLUTION OF SALTS IN WATER

Water dissolves most minerals and nutrients that our food contains. This helps in easy absorp on of the
dissolved materials by the body. Water also dissolves waste materials. These waste materials are later
removed by the kidney. Therefore, we can say that water is a good solvent.
A salt consists of posi ve and nega ve parts. When it dissolves in water, the posi ve part of the salt gets
a racted to the nega ve part of water and the nega ve part of the salt gets a racted to the posi ve part
of water. As a result, the salt disappears. This process can be physical or chemical which depends on the
salt or compound taken with water.

Dissolu on of sodium chloride in water represented in the form of an equa on.
–
+
NaCl (s)  Na (aq) + Cl (aq)
162