Carbon Monoxide

Carbon monoxide is an odourless and colourless gas, which is produced by the incomplete combustion of various fuels. The carbon monoxide formula is CO, i.e. it is a covalent compound of carbon and oxygen, in which carbon is negatively charged, and oxygen is positively charged. It is highly toxic to humans and results in carbon monoxide poisoning, which causes nausea, dizziness, and fatigue. It is used to synthesise hydrogen gas, which is further used to manufacture ammonia. It is crucial in many essential processes like drug production, fragrances, etc. It is used as a ligand to coordinate with metal complexes in chemistry. 

Sources of Carbon Monoxide

It is mainly formed when a fuel is not burnt completely. Carbon-containing fuels are methane, coal, propane, wood, kerosene, etc. Incomplete combustion occurs when there is not enough oxygen present in the atmosphere.

4CH4 + 5O2 → 2CO + 8H2O + 2C (equation for incomplete combustion of methane)

Industrially, it is produced by passing oxygen through a bed of coke (low-quality carbon-containing coal). It forms carbon dioxide, which reacts with coke to form carbon monoxide at high temperatures.

Boudouard Reaction:  C + CO2 → 2CO

Water Gas

The mixture of hydrogen gas and carbon monoxide is known as water gas. It is highly flammable. It is produced by passing steam over red hot coke.

C + H2O → CO + H2 

It has several uses. It is used to remove carbon dioxide gas from fuel cells. The pure hydrogen obtained via this reaction is used to synthesize ammonia (NH3). 

Carbon Monoxide Poisoning

Carbon Monoxide is a toxic gas that displaces the oxygen in the body upon inhalation and causes poisoning. Being colourless and odourless, we can never know when it is present around us in high quantity. It combines with haemoglobin in our bodies and does not let oxygen bind with it. The normal gas exchange processes of the body stop, which can lead to death also if not treated on time.

In the olden ages, it was used as a weapon. During the holocaust, the inmates were exposed to CO, leading to mass death or genocide. Earlier before, Roman prisoners were killed by Hannibal during the Second Punic War using carbon monoxide. This itself explains how lethal carbon monoxide can be at high concentrations. Hence, it is important to have proper ventilation at home as several household appliances like stoves, room heaters, and furnaces can release CO.

A Major Pollutant

Carbon monoxide is a major pollutant. It is a product of vehicular emissions that adds up to the atmosphere. It leads to ground-level ozone formation. Ozone in the stratosphere is crucial for the existence of life on Earth as it protects us from the sun’s harmful ultraviolet rays. However, on the ground level, it is unwanted.

Moreover, it is not a greenhouse gas on its own, but it leads to the indirect production of greenhouse gases like methane and carbon dioxide. Controlling its concentration has been a significant challenge for world governments and scientists.

As a Ligand

In chemistry, CO is mainly used as a ligand, referred to as carbonyl. Ligands are the compounds that coordinate with a metal atom (majorly transition metals like nickel, cobalt, platinum, iron, etc.). Without going into too much chemistry, CO binds with metals in low oxidation states to facilitate back-donation from metal to carbonyl. 

This property makes it indispensable in metallurgy. It is used to refine metals like nickel. The process to refine nickel with the help of carbonyl is called Mond’s Process, which Ludwig Mond first devised in 1890. 

Mond’s Process: Ni (impure) + 4CO → Ni(CO)4 → Ni (pure) + 4CO

Impure nickel is reacted with four equivalents of carbon monoxide to form Ni(CO)4, a volatile compound. It decomposes to nickel and carbonyl at higher temperatures (450 – 470K). The nickel thus obtained is pure and free from any impurity. 

Uses of Carbon Monoxide

Wood-Gas: In places with a limited fuel supply, wood gas (or syngas) was used. It is a mixture of gases containing 50% nitrogen, 20% CO, 18% hydrogen, 8% carbon dioxide, and 4% methane. During war times (especially World War II), to accommodate for the scarcity of fuel, wood gas was used in vehicles. In the presence of oxygen, it burns to produce heat, water vapour, and carbon dioxide (normal byproducts of combustion).

To prepare chemical compounds: CO is used to prepare compounds like methanol, other alcohols, and aldehydes. CO mixed with hydrogen (water gas) produces methanol. It can also produce hydrocarbon fuels by facilitating the formation of the carbon-carbon bond.

To preserve meat: Although CO is harmful to health, it can be consumed in minute amounts. It is used in the packaging of meat products and seafood like fish. It acts as a preservative and also keeps the food items fresh-looking. It gives the meat a bright-red colour as it reacts with myoglobin to form carboxy myoglobin. 

Conclusion 

Carbon monoxide is an oxide of carbon that exists in gaseous form. It is detrimental to human health and can cause CO poisoning. It is also harmful to the environment as it is a major pollutant released from vehicular emissions or incomplete combustion of carbon-based fuels. However, it also has several uses in the field of chemistry. It is used to refine metals and is a major component of water gas and syngas. The latter is used to power vehicles to this day in fuel-scarce regions.