Page 175 - ICSE Chemistry 8

Activity 8.3

Aim: To observe the eff ect of changing pressure on the freezing point of water
Materials required: Two ice cubes
Procedure
• Take two ice cubes and press them together by exer ng pressure on both the cubes.

Observa on: When you apply pressure on the ice cubes they join together to form one big cube. This
happens due to decrease in mel ng point of water which leads to mel ng of ice and thus water is formed.
• Now release the pressure and see what happens.
Observa on: When the pressure is released, the water freezes into ice. This joins the two ice cubes
together. This phenomenon is known as regela on.

• Density: Most liquids expand on hea ng and contract on cooling. However, water shows an
unusual property. It contracts on cooling ll the temperature reaches 4°C. Therea er it expands
when cooled below 4°C. This property is known as anomalous expansion of water.
Due to this property, the density of water is maximum at 4°C. But if it is cooled further water
expands to become less dense. At 0°C water freezes to form ice. The density of ice at 0°C is less
than the density of water, unlike the other liquids. This is the reason why ice fl oats on water.

Activity 8.4

Aim: To show that ice is lighter than water
Materials required: A glass, few ice cubes, some water ice cubes

Procedure water
• Take a glass. Add a few ice cubes to it.
• Now, add water to the glass. ice cubes
Observa on: The ice cubes immediately come to the surface of the water and start fl oa ng.
Conclusion: This shows that ice is lighter than water.

• Heat and electrical conduc vity: Pure water is a bad conductor of heat and electricity.

• Specifi c heat: Water has high specifi c heat. This means that water absorbs large amount of heat
energy before it begins to heat up and also it releases heat energy slowly when it cools down. In
other words, water neither heats up quickly nor cools down quickly. This feature makes water an
excellent cooling agent.
Water is used as a coolant in car engines, factories, nuclear reactors, etc.

The cooling eff ect of water also helps in modera on of the earth’s climate. In coastal areas, breeze
generally blows from the sea to the land during the day and from the land to the sea during the
night. During the day, land heats up more quickly than water. This is because water has a higher
heat capacity than land. Therefore, air over the land becomes warmer and rises up. Air from the
sea which is compara vely cooler, rushes to take its place. This creates a circulatory mo on of air

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