Topic 1 Air

                    Air 

Human beings are inseparable from the air at all times. Without air, there will be no life, and there will be no vibrant earth.

1. What is air composed of

More than 200 years ago, the French chemist Lavoisier studied the composition of air with a quantitative method. He put a small amount of mercury in a closed container and heated it continuously for 12 days, and found that part of the silver-white liquid mercury turned into red powder, and at the same time the volume of the air in the container was reduced by almost 1/5 . He studied the remaining 4/5 volume of gas and found that this part of the gas could neither provide breathing nor support combustion. He believed that these gases were all nitrogen (the Latin original meaning is " cannot support life").

Lavoisier collected the red powder generated on the surface of mercury, put it in another smaller container and heated it again, and obtained mercury and oxygen , and oxygen The volume is exactly equal to the reduced volume in the closed container. He added the obtained oxygen to the remaining 4/5 volume of the gas in the previous container, and the resulting gas had exactly the same properties as air.

Through these experiments, Lavoisier came to the conclusion that air is composed of oxygen and nitrogen , of which oxygen accounts for about 1/5 of the total volume of air.

Following the principle of this famous experiment in history, we will measure the oxygen content in the air.

Add a small amount of water into the gas collecting bottle and divide the space above the water into 5 equal parts. Secure the hose with spring clips. After igniting the red phosphorus in the flint spoon, put it into the bottle immediately and plug the stopper tightly to observe the phenomenon of red phosphorus burning. After the red phosphorus is extinguished and cooled, open the spring clip to observe the experimental phenomenon and the change of fishing on the water surface.

In this reaction, red phosphorus (chemical symbol P) reacts with oxygen in the air to form a new substance called phosphorus pentoxide (chemical symbol P 2 O 5 ) . This response can be expressed in words as follows:Red phosphorus plus oxygen to Phosphorus pentoxide

The level in the gas cylinder rises by about 1/5, indicating that the oxygen in the air is consumed, and the consumed oxygen accounts for about 1/5 of the air volume .

Before the end of the 19th century, it was believed that the air contained only oxygen and nitrogen. Later, people discovered rare gases such as ammonia, gas, chlorine, gas, gas, nitrogen, etc., and then realized that there are other components in the air besides oxygen and nitrogen. At present, people have been able to accurately determine the composition of air by experimental methods.

Through experiments, the composition of air is calculated by volume, which is about 78% nitrogen, 21% oxygen , 0.94% rare gas , 0.03% carbon dioxide , and 0.03% other gases and impurities .

A substance formed by mixing two or more substances, such as air, is called a mixture , and the various components that make up the mixture maintain their respective properties.

Nitrogen, oxygen, carbon dioxide, etc. are all made of one substance and are all pure substances. Pure substances can be represented by chemical symbols, such as nitrogen can be represented by N2, oxygen and carbon dioxide can be represented by O2, CO2. The red phosphorus used in the above experiments and the resulting phosphorus pentoxide were also pure substances.

2. Air is a precious resource

Various components in the air are widely used as raw materials in chemical industry, steelmaking, petroleum processing, transportation, electric light source and other fields, and are important resources for human production activities.

1、oxygen

In the past, people once called oxygen "nourishing Qi", which fully illustrates the importance of oxygen. Pure oxygen is used in medical first aid, fuel combustion is inseparable from oxygen, and oxygen is used in steelmaking, gas welding, chemical production and aerospace.

2、Nitrogen

Nitrogen has a wide range of uses, and it is an important raw material for the manufacture of nitric acid and nitrogen fertilizers; due to its inactive chemical properties, it is often used as a protective gas, such as nitrogen is often used as a protective gas when welding metals, nitrogen is filled in bulbs to prolong service life, food packaging Nitrogen is filled in the middle to prevent corrosion; medically, surgery can be performed under liquid nitrogen freezing anesthesia; superconducting materials can display superconducting properties in the low temperature environment of liquid nitrogen.

From the fact that red phosphorus cannot continue to burn in nitrogen, it shows that nitrogen does not support combustion. Many experimental facts have shown that the chemical properties of nitrogen are not as active as oxygen.

3、rare gas

In the composition of air, rare gases ② (nitrogen, gas, gas, gas, gas, and nitrogen) account for a small proportion, but they are a very important class of gases. They are colorless, odorless and chemically inert.

Rare gases are widely used in production and scientific research. For example, rare gases can emit different colors of light when electrified, and can be made into electric light sources for various purposes, such as navigation lights, strong lights, flash lights, neon lights, etc.; nitrogen can be used to create low-temperature environments.

3. Protect the air

Clean air is very important to humans and other animals and plants. However, with the development of industry, the harmful gas and smoke discharged into the air have polluted the air. Polluted air can seriously damage human health, affect crop growth, and destroy ecological balance. Global warming, ozone depletion and acid rain are also related to air pollution.

In order to make the sky bluer, human beings are taking active actions, such as strengthening air quality monitoring, improving environmental conditions, using clean energy, actively planting trees, afforestation, and grass to protect the air.

You should know after finishing this topic

1.The composition of air is approximately by volume: 21% oxygen , 78% nitrogen , 1% O

2.A pure substance consists of one substance; a mixture consists of two or more substances. Oxygen, nitrogen, etc. are pure substances, and air is a mixture.

3.Air is a precious natural resource, and it is necessary to protect the air and prevent air pollution.