Water and its properties
The hydrosphere is the Earth’s water shell: oceans, seas, lakes, rivers, glaciers and groundwater. Water covers about three-quarters of the Earth’s surface, so the Earth is called the “Blue planet”. Water is in the body of every living thing: more than half of a person’s body (about 60%) is water. Pure water is colourless, tasteless, odourless and transparent. River water is cloudy because soil is mixed in, and sea water looks blue when deep because water absorbs the red part of light more and the blue part is returned. In nature water exists in three states: ice, liquid water and vapour. A remarkable property is that ice is lighter than water, so it floats. If ice sank, lakes and rivers would freeze to the bottom in winter and fish would die; instead the ice layer covers the water and protects it from the cold. Water dissolves many substances: sugar and salt dissolve, sand, soil and vegetable oil do not. Distilled water is tasteless; mineral water contains useful salts.
Experiment: pour water into three glasses; add sugar to the first, sand to the second and vegetable oil to the third and stir. See which dissolves and record it in a table. Drop an ice cube in water and watch it float.