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Carbon Dioxide

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CARBON DIOXIDE

Carbon dioxide is a colourless and odourless gas. It occurs in the atmosphere ( 0.03% by volume ) but has a short residence time in this phase, as it is both consumed by plants during photosynthesis and produced by respiration and by combustion. It is charecterised by

  1. Soluble in water, ethanol and acetone.

  2. Its density is 1.977 g/dm3 .

  3. It is about 1.5 times as heavy as air and can be poured downward like water.

  4. Melting point -56.6OC.

  5. Boiling point -78.5OC.

  6. It can be easily liquefied under pressure ( approximately at 50- 60 atm)

  7. It is a nontoxic gas although animals die in it due to the lack of oxygen.

PREPARATION

  1. In the laboratory it can be readily prepared by the action of dilute acids on metal carbonates and bicarbonates.

    2. CaCO3 + 2HCl è CaCl2 + H2O + CO2

    NaHCO3 + 2HCl è NaCl + H2O + CO2

  2. Commercially, it is prepared by heating the carbonates of heavy metals.

    3. Heat

    CaCO3 è CaO + CO2

    2NaHCO3 è Na2CO3 + CO2

  3. it can also be obtained from alcoholic fermentation

Sugar è C6H12O6 è 2C2H5OH + 2CO2

CHEMICAL PROPERTIES

  1. Oxidising property

    2. Zn + CO2 è ZnO + CO

    C + CO2 è 2CO

  2. Acidic nature

It is an acidic oxide

  • It dissolves in water forming unstable carbonic acid

H2O + CO2 è H2CO3

  • With alkalies, CO2 combines to form two series of salts, carbonates and bicrbonates

2NaOH + CO2 è Na2CO3 + H2O

with excess of the carbonate is converted into bicarbonate

Na2CO3 + H2O + CO2 è 2NaHCO3

  1. Certain metals (active metal) continue burning in the presence of CO2 .

4Na + CO2 è 2Na2O + C

Na2O on further reacting with CO2 gives Na2CO3

Na2O + CO2 è Na2CO3

USES

  1. It is used in the manufacture of carbonated drinks ( aerated water).
  2. Liquid CO2 is used as a fire extinguisher.
  3. Solid CO2 (dry ice) is used in refrigeration.

  4. A mixture of oxygen and CO2 ( 5- 10 %), known as carbogen, is used for artificial respiration in the case of victims of carbon monoxide poisoning and pneumonia patients.

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