Composition of air

Oxygen occupies 20.9 percent of the air. This gas is produced by plants during photosynthesis as indicated by the equation.

Oxygen can also be prepared in the laboratory starting from different compounds. For example, it can be prepared using potassium chlorate as shown in the equation,

Explanation

1. Reactant: Potassium chlorate ($\text{KClO}_3$) is heated.
2. Catalyst: Manganese dioxide ($\text{MnO}_2$) acts as a catalyst to speed up the decomposition.
3. Products: Potassium chloride ($\text{KCl}$) and oxygen gas ($\text{O}_2$) are formed.

The importance of oxygen gas

Oxygen gas is crucial for the environment and living organisms. Its uses span various fields, including gaseous exchange, hospitals, welding, transportation facilities, and water treatment and purification.

1. Gaseous exchange

   Oxygen gas is used by different living organisms such as human beings and other animals. When oxygen is inhaled into the lungs, it is captured in the blood and transferred to body cells. In the body, the gas helps in the breakdown of food to produce energy. The gas is also used by small organisms. Oxygen gas is absorbed through the skin of small organisms such as worms to the cells.

   

   A diver using oxygen gas in deep water

   During the night, plants use oxygen gas to produce energy. That is why it is advised not to put plants in sleeping rooms with insufficient air supply. Astronomers, divers, and mountain climbers carry with them oxygen gas in cylinders for their use. Oxygen gas is also pumped into underground mines to ensure miners have sufficient supply of it.

2. Hospitals

   Oxygen is stored in special cylinders for use by patients in hospitals. For example, premature babies have breathing problems. They fail to use their lungs for gaseous exchange. Therefore, they use oxygen from a special machine that enables them breath. Likewise, patients with breathing problems especially those in critical condition, use special oxygen generating machines.

   

   A patient at hospital using oxygen

3. Welding

   Oxygen gas is used in welding. The gas facilitates the burning and softening of metals to be joined together.

   

   A person welding using gas

4. Wastewater treatment and purification

   Wastewater from residential areas, industries, business areas and from hospitals can be purified and reused. This is done using microorganisms such as bacteria found in the water. In order for the microorganisms to survive in the water, oxygen gas is blown into the water. Air blowing depends on the types and amount of chemicals present in the water. Thus, water must be investigated to find out the types and amount of chemicals present during treatment.

5. Transport

   Many transport facilities on land, water and air use fuel. The fuel is burnt so as to produce energy. The energy enables these facilities to move on the ground, and float in the air and on water. Oxygen is used to burn the fuels used in these facilities.

Carbon dioxide gas is present in the air at 0.03 per cent. Carbon dioxide is made up of two elements, which are carbon and oxygen. This gas has neither smell nor colour. In breathing, living things exhale carbon dioxide.

Activities such as fermentation, burning and rotting of things produce carbon dioxide. Likewise, in the laboratory, carbon dioxide is prepared by reacting carbonates and acids as shown in the following chemical equation:

The importance of carbon dioxide gas

1. Role in photosynthesis

   Plants use carbon dioxide during photosynthesis to manufacture their food and release oxygen as a by-product. This process is essential for maintaining the balance of gases in the atmosphere.

   

   Sources of oxygen and carbon dioxide

2. Refrigeration

   Carbon dioxide helps keep things fresh in refrigerators, maintaining a suitable environment for food storage.

3. Fire extinguishing

   Carbon dioxide is stored in cylinders and used as a fire-extinguishing agent.

   

   Carbon dioxide fire extinguisher

4. Chemical fertilizer production

   Carbon dioxide is used in the manufacturing of chemical fertilizers, contributing to agriculture and food production.

5. Baking

   Carbon dioxide produced by yeast is used to raise bread dough in bakeries and homes, ensuring soft and fluffy baked products.

6. Drink preservation

   Carbon dioxide is used to preserve and carbonate drinks such as soda and juice, enhancing their taste and shelf life.

Harmful effects of carbon dioxide gas

1. Increased production

   Carbon dioxide levels are rising due to industrial and human activities. Excessive carbon dioxide production can cause serious environmental problems.

2. Role of plants

   Plants play a vital role in reducing carbon dioxide levels in the environment. Planting more trees and avoiding unnecessary deforestation are important steps to mitigate carbon dioxide accumulation.

3. Greenhouse effect

   Carbon dioxide forms a layer in the atmosphere that traps heat, preventing its loss from the Earth's surface. This results in a rise in temperature, contributing to global warming and climate change.

4. Melting of ice

   Increased temperatures lead to the melting of polar ice caps, causing a rise in ocean water levels, which poses risks of flooding and habitat loss.

Composition of air

1. Nitrogen gas is the most abundant gas in the air, constituting 78% of all atmospheric gases.
2. It is produced through:
   • Geological activities
   • Agricultural activities
   • Animal husbandry
   • Urban waste

Role in plant and animal nutrition

1. Nitrogen is essential for the production of proteins in both plants and animals.
2. In the soil, nitrogen gas is converted by bacteria into usable elements or compounds. These are absorbed by plant roots along with water as nutrients.
3. A deficiency of nitrogen in the soil:
   • Retards plant growth
   • Causes yellowing of leaves
   • Reduces crop production and yields

Uses of nitrogen

1. Fertilizer production
   • Nitrogen gas is crucial for the production of industrial fertilizers, such as:
     • Urea
     • Double Ammonium Phosphate (DAP)
     • Nitrogen, Phosphorus, and Potassium (NPK)
     • Sulphate of Ammonia (SA)
     • Calcium, Ammonia, and Nitrogen (CAN)
2. Industrial applications
   • Nitrogen is used in the production of:
     • Nitric acid
     • Various dyes
     • Nylon
3. Medical applications
   • Nitrogen gas is used in hospitals for preservation purposes, including:
     • Male and female gametes
     • Cells
     • Nerves
     • Blood
   • It is also used to preserve items at specific temperatures.

This is an inert gas found in the air. Argon makes 0.90 per cent of the air. Argon is an inert gas because it cannot react with other elements to form compounds. It is odorless and colourless. The gas is used in electric bulbs and fluorescent tubes. Argon is also used in metal cutting and welding.

Water exists in three states, which are solid, liquid and gas. Water vapour exists in the air in different amounts depending on the area. The vapour comes from water bodies such as oceans, lakes, rivers, and other sources.

Plants lose water to the atmosphere in the form of vapour. In the atmosphere, the vapour cools and condenses into droplets that fall as rain. Animals also lose water in the form of vapour through sweating and breathing.