18. Explain the following:
(a) Water pipes in colder countries often burst in
winter
(b) In winter, water tank (or ocean) starts freezing
from the surface and not from the bottom,
(c) Fishes survive in ponds even when the
atmospheric temperature is below 0°C,
(d) A hollow glass sphere which floats with its entire
volume submerged in water at 4°C, sinks when
water is heated above 4°C.
(e) A glass bottle completely filled with water and
tightly closed at room temperature, is likely to
burst when kept in the freezer of a refrigerator.
(R)
ENGECYFI
Answers
Water in pipes freeze in cold countries. Due to the anomalous expansion of water, it expands instead of contacting when there is a fall in temperature below 4°c. So, the water pipes burst due to the excess space consumed by the ice after freezing.
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The density of the water is highest at 4oC. So the at winter the water having temperature 4oC goes to the bottom of the tank and the water having less temperature will be at the surface. Hence the freezing starts at the surface
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After sufficient thickness of ice is formed it prevents further loss of heat from the bottom layers of water. This is why fishes and other aquatic animals and plants can survive in ponds and other water bodies even when the atmospheric temperature reaches or is well below 0°.
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This is the reason why the hollow sphere stays a float and will only sink after the water is heated above the 4 degrees celcius. The sinking is because, when the water is heated above the 4 degrees celcius, it starts to expand and its density falls hence not able to keep the sphere afloat
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Water has a greater density than ice. This means that the volume occupied by ice is greater than the volume occupied by water for the same mass. 1 kg of water in a 1 Litre bottle will have less volume than the same 1 kg when it becomes ice. This is because between 0 - 4°C, water expands and forms a more open ice structure. The ice then occupies too much volume as a result of the expansion, causing the bottle to break.
Answer:
Water pipes burst because the water inside them expands as it gets close to freezing, and this causes an increase in pressure inside the pipe. When the pressure gets too high for the pipe to contain, it ruptures.
b) In winter, when the atmospheric temperature starts falling well below 0℃ the water at the surface of the tank or the ocean initially at temperature of 4℃ begins to radiate heat to the atmosphere. So the temperature of water starts falling when the temperature of water at the surface falls, water contract, so its density increases and therefore it sinks to the bottom. This happens due to an anomalous expansion of water.
c) Fishes can survive in pond even though the temperature is 0℃ because till 4℃ water contracts but when the temperature reaches below 4℃ water expands. This is called the anomalous property of water.
d) This is because at 4℃, the water is at its peak density, this high density is due to the fact that water at this temperature gets more contracted than usual and will have low volume with a high density. This is the reason why the hollow sphere stays floats and will only sink after the water is heated above 4℃, the sinking is because when the water is heated above 4℃ it starts to expand and its density falls hence not able to keep the sphere afloat.
e) It is due to the anomalous expansion or strange behavior of water. The expansion of water takes place as it is cooled from 4℃ to 0℃. This behavior is unusual because most substances contract when they are cooled, but water expands on solidifying. Due to this expansion a glass bottle completely filled with water and tightly closed at room temperature is likely to burst when it is kept in fridge.