Topic 2 Oxygen

Topic 2

Oxygen

Under standard conditions, the density of oxygen is 1.429 g/L, which is slightly larger than that of air ( 1.293 g/L ) . It is not easily soluble in water, at room temperature, only about 30 mL of oxygen can be dissolved in 1 L of water . At a pressure of 101 kPa , oxygen turns into a light blue liquid at -183 ℃ , and a light blue snowflake-like solid at -218 ℃.

Industrially produced oxygen is generally stored under pressure in blue steel cylinders.

The wooden sticks with sparks can re-ignite in oxygen, indicating that oxygen can support combustion.

( S02 ) gas with a pungent odor and release heat. This reaction can be represented as follows: Sulfur plus Oxygen to Sulfur Dioxide

When the iron wire is heated in the air, the iron wire can only produce red heat and cannot be burned; but when the thin iron wire is ignited in oxygen, it can burn violently and sparks radiate. Iron reacts with oxygen to generate black iron oxide solid. This reaction can be expressed as follows：Iron plus Oxygen to Iron Tetroxide

Through the above several experiments, we can see that combustibles burn more violently in oxygen than in air. For example, sulfur burns in air with a faint pale blue flame, but in oxygen burns more vigorously with a blue-violet flame. Also, certain substances that cannot burn in air can burn in oxygen . This shows that the chemical properties of oxygen are relatively active, and it also shows that the combustion of substances in the air actually reacts with the oxygen in it. Since the oxygen content in the air is relatively small, the combustion in the air is not as violent as in oxygen.

Through experiments and discussions, we found that the reactions between oxygen and phosphorus, sulfur, and iron have a common feature: they all react from two substances to form another substance. We call the reaction in which two or more substances form another substance a compound reaction.

These three reactions have another feature in common: they are all reactions between substances and oxygen. These reactions are oxidation reactions. Oxygen provides oxygen in the oxidation reaction and it has oxidative properties.

Combustion of substances in oxygen is a violent oxidation reaction, but not all oxidation reactions are as violent as combustion and emit light and heat. Some oxidation reactions proceed very slowly, and are not even easily detected. This oxidation is called slow oxidation. In life, there are many examples of slow oxidation, such as the respiration of animals and plants, food rot, vinegar brewing, and farm manure decomposing, all of which involve slow oxidation of substances.

After finishing this topic, you should know

1.The chemical properties of oxygen are relatively active, can support combustion, and can react with phosphorus, sulfur, iron, etc. under certain conditions.

2.The reaction in which two or more substances form another substance is called a compound reaction. The reaction of a substance with oxygen is an oxidation reaction.