Water exists on Earth in three physical states. In the water cycle, water changes from one physical state to another through processes like evaporation and condensation. Substances which are soluble can dissolve in water to form solutions, whereas substances which are insoluble cannot. Water exists in natural form contain impurities and microorganisms, and requires purification and proper treatment before it could be consumed as drinking water. Water is a precious natural resource, therefore we should conserve water.

In this Unit, students will learn about the above aspects of water, and perform practical works and investigations, e.g. observing the change in state of substance, investigating the factors affecting the rate of dissolving, designing and making a filtration column. These would help students develop some science process skills as well as the ability to integrate and apply knowledge and skills of different disciplines.

 

Learning about the processes in the water cycle will help students appreciate the unifying concepts “change and constancy”. While investigating how some factors affect the rate of evaporation and the rate of dissolving of substances in water, students will recognise the unifying concepts “evidence and models”.