CARBON AND ITS COMPOUNDS
GRDAE 8
Lesson 3
CARBON DIOXIDE
Occurance- In air- 0.03 %
Added to atmosphere by
1) Respiration
2) Burning of carbon compounds
3) Decay and decomposition of organic matter
4) In combined state as- metallic carbonates and bicarbonates in earth's
crust.
Preparation
a) Burning carbon compounds- in air
C + O2 ----> CO2
CH4 + 2O2 ----> CO2 + 2H2O + Heat
b) By action of dil acids on carbonates and bicarbonates.
Na2CO3 + H2SO4 --------> Na2SO4 + CO2 + H2O
CaCO3 + 2HCl --------> CaCl2 + CO2 + H2O
NaHCO3 + HCl --------> NaCl + CO2 + H2O
Ca(HCO3)2 + 2HNO3 --------> Ca(NO3)2 + 2CO2 + 2H2O
Laboratory Preparation
By the action of dil. HCl on Calcium carbonate (marbel chips)
CaCO3 + 2HCl (dil.) -----> CaCl2 + H2O + CO2
The CO2 passed over conc. H2SO4 to absorb moisture.
The pure and dry CO2 is collected by the upward displacement of air as
cabon dioxide is 1.5 times heavier than air.
Note : H2SO4 is not used in the above process as it forms insoluble CaSO4
which settles on the marbel chips and reduces the reactivity gradually.
Physical Properties
Colour - Colourless
Odour-Odourless
Nature- Non poisonous (but does not support respiration)
Density- 1.5 times heavier than air
Solubility- Fairly soluble in water
Liquefaction - Easily liquified at about 70 atms pressure at ordinary
temperatures.
Dry Ice- Carbon dioxide solidifies on cooling at -780C to form white
solid- called dry ice.
Preparation of dry ice- Taking carbon dioxide to high pressure and
suddenly allowing it to expand through a small nozzle. Carbon dioxide
solidifies to for dry ice.
Chemical properties :
a) Combustibility- Non supporter of combustion.
b) Nature- Slightly acidic in nature - turns blue litmus paper red.
Recations
1. Water
CO2 + H2O ----> H2CO3
carbonic acid (weak acid)
2. Ammonia
2NH3 + CO2 ----> (NH2)2CO + H2O
urea
3. Carbon
CO2 + C -----> 2CO
4. Magnesium
Mg + CO2 ----> 2MgO + C
5. Basic oxides to metal carbonates.
Na2O + CO2 -----> Na2CO3
6. Lime water to insoluble calcium carbonate.
when carbon dioxide is bubbled into lime water (solution of calcium
hydroxide), lime water turne milky due to the formation of insoluble
calcium carbonate.
Ca(OH)2 + CO2 ----> CaCO3 + H2O
In excess of lime water, it forms soluble calcium bicarbonate, and
milkiness disappears.
CaCO3 + H2O + CO2 ----> Ca(HCO3)2
Uses
1. Soda Manufacture- by passing CO2 into water under pressure.
2. Dry ice- Used as a refrigerant for preservation of foods.
3. Baking food items (in cakes,bread). Baking powder (NaHCO3) mixed
with dough, liberates carbon dioxide which makes the dough light and
porous.
4. Fire extinguishing- As a non supporter of combustion.
5. Photosynthesis by green plants.
Fire Extinguishers
a) Soda acid fire extinguisher- Used for general fire.
NaHCO3 and H2SO4 reacts to liberate CO2 in solution form.
b) Liquid CO2 fire extinguisher : Liquid carbon dioxide solidifies on
release gives snowy dry ice. It is used to fight electrical and oil fires.
