Topic 3 Composition of water

Topic 3

Composition of water

For a long period of time, water was once regarded as an " element " . It was not until the end of the 18th century that people finally understood the composition of water through the research on the formation and decomposition experiments of water.

The combustion experiment of studying hydrogen is the beginning of people's understanding of the composition of water.

Hydrogen is a colorless, odorless, insoluble gas with a lower density than air. When hydrogen burns in the air, it produces a light blue flame; hydrogen mixed with a certain amount of air or oxygen will explode when it encounters an open flame. Therefore, before igniting the hydrogen gas, the purity must be checked. The method is shown in Figure 4-23 . When the hydrogen gas is ignited, a sharp popping sound indicates that the gas is impure, and a small sound indicates that the gas is relatively pure.

After studying this topic, you should know

1.Water is composed of hydrogen and oxygen elements.

2.An element is a pure substance composed of the same elements.

3.Compounds are pure substances composed of different kinds of elements.

4.Compounds composed of two elements, one of which is oxygen, are called oxides.