Question

Sort the sentences based on whether they are correct or incorrect. Water boils at a temperature below 100°C at higher altitudes. Water expands on freezing. Water contracts on freezing. Water boils at a temperature below 100°C in a pressure cooker. The density of water decreases on freezing. Water boils at 100°C under normal pressure.

Answer 1

Correct sentences

• Water boils at a temperature below 100°C at higher altitudes-At higher altitudes where atmospheric pressure is low, less heat is required to make water boil.Increase in elevation, decreases the amount of energy required to make water boil.The boiling point of water is less at higher attitudes because the atmospheric pressure is already low thus less vapor pressure is needed to create a balance thus less heat will be required.

• Water expands on freezing.Before 4°C water behaves normal in that it contracts as it cools.However, at 4°C it starts to expand at a smaller margin until the freezing point is reached.During freezing, it expands.

• The density of water decreases on freezing.As water cools towards 4°C,it contracts.The contraction will result to increased density of course.However, when it reaches 4°C the behavior changes because it attains maximum density at 4°C.Beyond this point, water density reduces as it nears the freezing point.
• Water boils at 100°C under normal pressure.The boiling point of at normal atmospheric pressure is 100°C.This is for the case of pure water.However, adding salt to water will increase its boiling point even when pressure is normal.

Incorrect sentences

• Water contracts on freezing.Water expands on freezing.The contracting effect is experienced before water starts to freeze.This is before it reaches 4°C.At 4°C the expansion process starts at a smaller margin and it reaches the highest during freezing.
• Water boils at a temperature below 100°C in a pressure cooker. In a pressure cooker, water boils at 121°C.This is because the water is sealed thus the pressures inside are increased and heat is trapped inside.This trapped heat further causes the water to boil faster as it it supplies extra energy to heat the water.