The main constituents of air are nitrogen and oxygen. It also contains carbon dioxide and water vapour in small amounts. Inert gases and ozone are also present in trace amounts in air. Apart from these gases, air also contains some impurities, like sulphur dioxide, hydrogen sulphide, nitrogen dioxide, dust particles, etc.
Carbon dioxide gas is one of the most important constituents of air. It was discovered by Van Helmont in 1630 by burning charcoal in air.
In 1775, Joseph Black obtained carbon dioxide by the action of dilute acids on metal carbonates. Later, Antoine Lavoisier studied the gas and named it acid carbonique. He found that the gas was an oxide of carbon, which dissolved in water to produce an acidic solution. Later on, it was named carbon dioxide.
Is Co2 Heavier than Air?
CO2 is heavier than air, and it insulates the burning substance by cutting off its supply of oxygen. If a burning candle or a smouldering match stick is introduced in a jar containing carbon dioxide, it extinguishes. This proves that the gas is a non-supporter of combustion. Carbon dioxide also helps to extinguish the fire because as it neither burns nor does it help in burning.
Experiment To show that carbon dioxide is heavier than air and a non-supporter of combustion
- Take a jar containing air. Introduce a burning candle in it.
- Tilt a jar containing carbon dioxide over the jar with burning candle.
- You will observe that the candle flame goes off.
- This is because carbon dioxide being heavier spreads over the flame and the air goes up.
- This also proves that carbon dioxide does not supports combustion.
In nature, carbon dioxide occurs in a free state as well as in its combined state.
(i) In a free state.
- About 0.03% – 0.04% by volume of carbon dioxide is present in air.
- It is also present in the rocks of volcanic regions.
- In natural water carbon dioxide is present in a dissolved state as it is fairly soluble in water.
(ii) In combined state :
It occurs as metallic carbonates and bicarbonates in the earth’s crust and also in sea shells. The chief minerals containing CO2, are dolomite (MgCO3.CaCO3), limestone (CaCO3), etc.
Along with it, all life forms are based on carbon-containing molecules like proteins, carbohydrates, fats, nucleic acid and vitamins. The exoskeletons and endoskeletons of various animals are also formed from carbonate salts.
Uses of Carbon Dioxide
1. In aerated drinks
Carbon dioxide is used in the manufacture of aerated drinks. The gas is dissolved in water under pressure to give soda water. When the pressure is released, the bottled gas escapes with a brisk effervescence that adds fizz to the drink. Common soft drinks are formed by dissolving carbon dioxide in a sugar solution.
2. Refrigeration and preservation of food stuffs
Solid carbon dioxide (dry ice) is used as a coolant and a refrigerant in ships for preserving food articles like fruit, vegetable, meat, etc., which otherwise perish easily. Also, if grains are kept in an atmosphere of carbon dioxide, they remain in good condition for a long period, without allowing insect attacks.
3. In hospitals
A mixture of 5% carbon dioxide and 95% oxygen, called carbogen, is used for artificial respiration. It is given to patients suffering from gas poisoning, pneumonia, drowning, etc.
4. In the manufacture of fertilizers (urea)
Urea is an important nitrogenous fertilizer. It is prepared when carbon dioxide and ammonia are heated at 200°C under very high pressure.
5. In the preparation of chemicals
Carbon dioxide is used to manufacture chemicals like washing soda (sodium carbonate) and baking soda (sodium bicarbonate)
6. In the baking industry : Carbon dioxide
is used to make the dough rise and become light. Baking powder is a mixture of baking soda (NaHCO3) and potassium hydrogen tartarate. When it is added to the dough, the ingredients of baking soda react to release carbon dioxide. As the gas rises through the dough, spaces are formed, thus making the dough porous and the cakes and bread spongy.
7. In photosynthesis
Photosynthesis is a natural process. It helps to maintain the required quantity of carbon dioxide in the atmosphere. Plants containing chlorophyll absorb carbon dioxide from the atmosphere and water from the soil in the presence of sunlight) to prepare their food (glucose). The other product released is oxygen gas.
Photosynthesis has its own great importance. It removes extra carbon dioxide from the atmosphere and restores oxygen. Also, vegetarian food stuffs like carbohydrates cannot be produced without photosynthesis.
How Heavier CO2 Helpful in Extinguishing fires
Fire extinguishers are devices in which carbon dioxide is produced in different forms for use as the extinguishing agent.
When a substance burns with a flame, the heat and the light, and often the smoke so produced, constitute “fire”.
For a fire to occur, the presence of a combustible substance and a supporter of combustion are required as well as attainment of the required ignition temperature is necessary. If any of the above conditions is not satisfied, a fire will not be produced, i.e. even if there is a fire already it will die out. This is the principle that is exploited for “fire fighting” purposes.
Some common types of fire extinguishers are :
- Soda-acid fire extinguisher
- Foam-based fire extinguisher
- Liquid carbon dioxide fire extinguisher
(i) Soda-acid fire extinguisher
It contains sulphuric acid and sodium bicarbonate, in separate chambers. When the apparatus has to be used, contact is made between the two chemicals and carbon dioxide is produced. The gas comes out in the form of a solution that extinguishes fire.
(ii) Foam-based fire extinguisher
It contains aluminium sulphate and sodium bicarbonate, in separate chambers. The two chemicals mix and react to form carbon dioxide and aluminium hydroxide, which come out together through the nozzle of the apparatus as foam. This foam is used to extinguish oil-fed fires because the foam covers the oil as well as cuts off the air supply to the fire.
(iii) Liquid carbon dioxide fire extinguisher
It is the most modern type of fire extinguisher. Liquid carbon dioxide is stored in a steel cylinder under pressure. When the valve of the cylinder is opened, the pressure falls and liquid carbon dioxide solidifies into white snow (dry ice), which can be used to put out both oil-fed and electrical fires.
Why Avoid Soda Acid
Why we cannot use soda-acid and foam types of fire extinguishers to fight an electrical fire? In these fire extinguishers, the extinguishing solutions are prepared in water which, being impure, conducts electricity. As a result, an electric shock could result, which could then lead to shortcircuiting and another fire.
Precautions to avoid fire accidents and fighting fire
(A) Taking care of combustible substances :
1. The premises of petrol pumps, LPG godowns, fire cracker shops should be out of bounds for all kinds of burning objects, fires and heat radiating hot articles. This is because the materials stored here are highly combustible, i.e. they have low ignition points.
2. At home we must see that combustible materials like furniture and synthetic textiles, do not come into contact with fire.
(B) Care to cut off the supply of air and lower temperature below ignition point
Once a fire has started it can be extinguished only by either cutting the supply of air or lowering the temperature below the ignition point. This can be done by :
(i) pouring water or sand over the fire.
(ii) applying carbon dioxide to the fire with the help of fire extinguishers.
(iii) putting off the main switch in case of an electrical fire.