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Carbon Monoxide

The various names of Carbon Monoxide (CO) are carbonous oxide, carbon (II) oxide, carbonyl etc. It is an odorless, colorless gas which is less dense than air.
The higher concentration of carbon monoxide can be toxic to humans and animals due to the great combining affinity of carbon monoxide with hemoglobin. It is a short lived and spatially variable gas in atmosphere which can be easily combined with oxygen to form carbon dioxide and ozone.

Carbon monoxide is a flammable and highly toxic gas. It is a neutral oxide of carbon element and burns in air to give carbon dioxide. For several chemical reaction, it acts as a good reducing agent. For example, to reduce cupric oxide to copper metal and to convert carbon dioxide to C and O2.

CuO + CO Cu + CO2

It is also an important industrial gas and widely used as a fuel and as an important reducing agent in the chemical industry.

 

Carbon Monoxide Molecule

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  1. The molar mass of carbon monoxide is 28.0g/mol that is the reason that it is less dense than air.
  2. It is soluble in non-polar solvent like chloroform, acetic acid, ethyl acetate and benzene etc.
  3. The carbon-oxygen bond length in carbon monoxide is 112.8 pm which is almost same as the bond length of a triple bond.
  4. Hence, some other molecules like nitrogen (N2), which has a similar bond length and nearly the same molecular mass shows many similar properties.
  5. Like the boiling point (82 K) and melting point (68 K) of carbon monoxide are nearly same as for N2 (77 K and 63 K, respectively).
  6. But the bond dissociation energy of carbon-oxygen bond in CO molecule is quite higher (1072 kJ/mol) than that of N2 (942 kJ/mol), hence the carbon-oxygen bond is stronger than nitrogen.
  7. Carbon monoxide is a polar molecule due to the difference in electronegativity of carbon and oxygen atom; there will be partial positive charge on carbon and partial negative charge on oxygen.
  8. The dipole moment of carbon monoxide molecule is 0.122D , directed towards oxygen atom.
  9. Since there are total ten valence electrons, two on carbon and four on oxygen.
  10. Six electrons involve in the formation of triple bond and the electropositive carbon.
  11. Due to this molecule can show three resonating structure and get stabilized.
  12. There is sp hybridization in carbon monoxide molecule with linear geometry.
  13. According to molecular orbital theory, carbon monoxide is a diamagnetic molecule with all paired electron.
Molecular Orbital Theory

Carbon Monoxide Synthesis

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Several methods are available for the preparation of carbon monoxide gas. There are a number of methods available for the preparation of carbon monoxide and on industrial scale, it is generally produced by using natural gas which mainly consists methane (CH4) gas and water gas (CO + H2) or by using producer gas (CO +N2).

Laboratory methods


1. Dehydration of formic acid in the presence of concentrated sulfuric acid forms carbon monoxide gas.

HCOOH H2O + CO

2. When carbon dioxide passes over heated carbon, it converts into carbon monoxide.

heat
CO2 + C 2 CO

3. Another method for the preparation of carbon monoxide is the heating of mixture of powdered zinc metal and calcium carbonate to form CO and zinc oxide and calcium oxide as residue.

Zn + CaCO3 ZnO + CaO + CO

Industrial production


On a large scale, carbon monoxide can be manufactured by using producer gas (a mixture containing mostly carbon monoxide and nitrogen) or natural gas(mainly consist of methane) or water gas (a mixture of hydrogen and carbon monoxide).

1. Producer gas is formed by combustion of carbon monoxide in the air with nitrogen at a very high temperature of around 800 °C in the presence of hot carbon. In an oven, air is passed through a bed of coke which initially produces carbon dioxide (CO2).

This carbon dioxide reacts with the remaining hot carbon to give carbon monoxide gas. This reaction is called as the Boudouard equilibrium. Reaction is exothermic in nature and produces a large amount of heat.

O2 + 2 C 2 CO (ΔH = −221 kJ/mol)

2. Like producer gas, water gas is also a good source of carbon monoxide. It is a mixture of hydrogen and carbon monoxide produced via endothermic reaction of steam and carbon.

H2O + C H2 + CO (ΔH =+131 kJ/mol)

3. Synthesis gas also termed as syngas is a good source of carbon monoxide. It is obtained from natural gas and other fuels. Syngas is a mixture of varying amounts of carbon monoxide and hydrogen gas.

Synthesis gas is produced by steam reforming of natural gas. Steam reforming occurs at high temperatures (700 - 1100 °C) and in the presence of a metal-based catalyst like nickel. In this reaction, steam reacts with methane to give carbon monoxide and hydrogen.

CH4 + H2O CO + 3H2

4. Since carbon is a good reducing agent, it also produces a byproduct of the reduction of metal oxide ores with carbon.
MO + C M + CO

Effects of Carbon Monoxide

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The main product of complete combustion of any organic compound is carbon dioxide and water. However the incomplete combustion of organic compounds in the limited amount of oxygen yields carbon monoxide.
Once the gas is inhaled, it becomes very harmful. Since carbon monoxide is easily absorbed through the lungs, it's easy for gas to circulate in body. Carbon monoxide has more binding affinity with hemoglobin compared to oxygen.
Hence, it can easily replace oxygen and can bound with hemoglobin. In the deficiency of oxygen, tissue becomes starved for it.

Effects of Carbon Monoxide

Due to high binding affinity of carbon monoxide, it forms carboxyheamoglobin (HbCO) which starved oxygen supplies in cell.
Carboxyheamoglobin


Exposure to carbon monoxide is most commonly accompanied by the following symptoms.
  • Headache, dizziness, nausea, shortness of breath on exertion, impaired judgment, chest pain and depression etc.
  • The low supply of oxygen to the blood leads to hypoxia myoglobin and mitochondrial cytochrome oxidase are thought to be adversely affected.
  • For the treatment of poisoning due to carbon monoxide, oxygen acts as the best medicine. Supply of oxygen provides hyperbaric oxygen therapy.
  • Oxygen acts as an antidote because the high concentration of oxygen forces to remove carbon monoxide from hemoglobin and turn the body with normal levels of oxygen.
  • Domestic carbon monoxide can be detected by using carbon monoxide detectors.
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