1. In nature
a) Carbon dioxide is used in photosynthesis by green plants to produce carbohydrates.
b) To induce natural breathing.2. To extinguish fires
Soda-acid fire extinguishers produce carbon dioxide to put out fires.
3. As a refrigerant
Solid carbon dioxide called "Dry ice" can provide temperatures as low as -109.3o F. It is superior to ordinary ice, for the following reasons:
i) It provides much lower temperature than ice.ii) It lasts longer.
iii) It freezes faster.iv) It does not wet the food being chilled, as it sublimes directly into gaseous state.
Dry ice must be handled carefully, as it causes injury on direct contact with skin.4. In liquefaction or solidification of gases
Powdered dry ice and ether or acetone, when mixed together, can reduce the temperatures to about -220oF. At this temperature it is used in liquefaction or solidification of gases.
5. Manufacture of fertilizer
Carbon dioxide is used extensively in the manufacture of urea, an important in nitrogenous fertilizer.
6. In the baking industry
Baking powder is used in all the food preparations. The addition of baking powder during baking, produces carbon dioxide which, makes the dough "rise". The small pores in a loaf of bread are the spaces in which carbon dioxide was formed (Fig.11.13).
Yeast is also used in baking instead of baking powder. It produces carbon dioxide by anaerobic respiration.
Remember :Baking powder contains starch, sodium hydrogen carbonate and an acid forming ingredient, such as tartaric acid of calcium hydrogen phosphate [Ca(H2PO4)2] or alum [Na2SO4.Al2(SO4)3.24 H2O].
7 a) In medicine
A mixture of 97% oxygen and 3% carbon dioxide, called carbogen is used to revive persons affected by carbon monoxide poisoning, pneumonia, asphyxiation etc.
b) Over production of hydrochloric acid in the gastric juice causes acidity. Health salts mostly contain sodium hydrogen carbonate, which reacts with the acid to form carbon dioxide. These salts thus liberate carbon dioxide and relieve the bloated feeling in the abdomen by pushing the other gases out of the abdomen.8. Manufacture of aerated drinks
Carbon dioxide is extensively used in aerated drinks. Increasing the pressure increases the solubility of the gas. The fizz in the drink is due to carbon dioxide being liberated when the pressure is reduced.
9. In commercial chemicals
Carbon dioxide is used in the manufacture of compounds like sodium carbonate, sodium hydrogen carbonate, white lead [Pb(OH)2.PbCO3], etc. In the manufacture of sugar it is used to precipitate lime.
10. Food storage
It is use to fill silos (storage bins) and containers, that are used for storing food grains. After the silos are packed with the food grains, carbon dioxide is pumped into the silos from the top. The gas being heavier then air, slowly sinks down, pushing out the air in between the grains. This prevents the growth of bacteria, fungus, etc. on the grains (Fig.11.14).
11. In the setting of lime mortar
The slaked lime present in the mortar combines with the carbon dioxide of the air to form a hard layered mass of calcium carbonate. When the walls are whitewashed with "milk of lime", a thick suspension of slaked lime in water, carbon dioxide of the air combines with the calcium hydroxide and forms a layer of calcium carbonate.
13. In the entertainment industry
Dry ice is used to create artificial clouds as special effects, for stage shows, films, discotheques etc. Dry ice is dropped into water; absorbing heat from the water, the solid carbon dioxide sublimes, carrying with it a lot of water vapor. These two together form thick white 'clouds'. But unlike real clouds, which are formed above due to the low vapor density of water vapor, the artificial cloud fills the floor of the stage, as the vapor density of carbon dioxide is 22. So while the lower part of the body of the artist is covered by 'cloud', the upper half is visible.
