Page 80 - ICSE Chemistry 6

Activity 4.5

Aim: To show that water expands on freezing
Materials required: A thick plas c bo le, some water, a marker, a refrigerator
Procedure

• Take a thick plas c bo le. Fill half of the bo le with water.
• Mark the level of water with a marker.
• Keep the bo le in the freezer.

Observa on: The level of water rises above the mark.
Conclusion: This shows that water when cooled below 4°C expands and freezes at 0°C.

It is due to the above property that glass bo les when fi lled completely with water break when kept in
the freezer.

Specifi c heat capacity: The amount of heat energy per unit mass required to raise the temperature of a liquid
–1
–1
by 1°C is called the specifi c heat capacity. Water has a high specifi c heat index of 4186 joule kg °C . Water
therefore takes me to get heated and hence used as a coolant in car radiators.
Latent heat of fusion of ice: The amount of heat energy required to change ice back to water at 0°C without
any change in temperature is called the latent heat of fusion of ice. The latent heat of fusion of ice is 80 cals/g
3
–1
or 334 × 10 joule kg which is equal to the amount of heat energy released when 1 kg of water solidifi es into
1 kg of ice at 0°C.
Latent heat of vaporiza on: The amount of heat energy required to change water into steam at 100°C without
–1
6
any change in temperature is called the latent heat of vaporiza on. Its value is 2.3 × 10 joule/kg which is equal
to the amount of heat energy released when 1 gram of steam condenses to form 1 gram of water at 100°C.
As steam contains more heat energy in the form of latent heat, therefore it causes more severe burns than
boiling water.

Activity 4.6

Aim: To fi nd applica on of specifi c capacity of water and of latent heat of fusion
Find two applica ons of specifi c heat capacity of water and two applica ons of latent heat of fusion
of ice. Discuss these applica ons in the class. You may use the Internet to collect informa on.

IMPORTANCE OF WATER

Water is an integral component of all living beings. It plays an Thirst for Knowledge
irreplaceable role in the survival and existence of living organisms.
• Vitreous membrane in the eye
Like humans, animals also contain a large propor on of water in has 99% water. It is the most
their body. About 80% of elephant body is water. watery part.

Water is important for humans and animals in the following ways. • Teeth and skeleton contain only
2% water. They are the least
• Diges on of food in the stomach takes place with the help
watery parts.
of water.

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