The properties , source and cycle of oxygen gas
The atmosphere contains oxygen gas that necessary for respiration process , It is a mixture of gases surrounding the Earth , It is attracted to Earth by gravity , It protects the Earth by absorbing ultraviolet radiations coming from outer space and it adjusts the temperature of the Earth’s surface .
Oxygen gas exists in the atmosphere in a gaseous state , it represents 21 % of the air volume of the atmosphere , oxygen molecule consists of two oxygen atoms .
The green plants are the main source of oxygen gas as they produced it during the photosynthesis process , oxygen gas is consumed in the respiration and combustion processes , So , the ratio of oxygen gas ( 21 % ) in the atmosphere is fixed .
In the photosynthesis process , the green plants ( the plants that have the chloroplasts ) take carbon dioxide from the air , the water and mineral salts from the soil and the sunlight ( light energy ) to produce the nutrients and oxygen gas .
The properties of oxygen gas
Oxygen gas has a neutral effect on litmus paper , It does not burn but helps in burning and it is heavier than the air so , It replaces the air , It scarcely dissolves in the water , it is a colorless , tasteless and odorless gas , It has the ability to combine directly with most elements forming oxides .
Combination of oxygen gas with elements
Oxygen gas combines with elements in two ways which are the oxidation process and burning process ( combustion ) , Oxidation is a slow combination between oxygen and element in the presence of moisture ( the water ) as iron rusting .
Iron rusting causes erosion and damage of ironware as the bridges pillars , and the method to avoid iron rusting is isolation of ironware by paints to protect them from rusting .
Burning ( combustion ) is a rapid combination ( union ) between oxygen and element producing heat and light , And the weight of the elements increases after combustion with oxygen as burning a piece of cleaning wire .