Carbon (IV) oxide, also known as carbon dioxide (CO2), is a chemical compound composed of one carbon atom and two oxygen atoms. It is a colorless, odorless gas that is naturally present in the Earth’s atmosphere and is essential to life on Earth, as it is used by plants during photosynthesis and by animals during respiration.

Carbon dioxide is also produced through various human activities, such as the burning of fossil fuels and deforestation, which can lead to an increase in atmospheric concentrations of the gas. This increase in atmospheric CO2 concentrations is a major contributor to global climate change, as carbon dioxide is a greenhouse gas that traps heat in the Earth’s atmosphere.

In addition to its role in climate change, carbon dioxide has many other uses in chemistry and industry. It is used in the production of carbonated beverages, as a refrigerant, and as a solvent for chemical reactions. Carbon dioxide is also a key ingredient in dry ice, which is used for refrigeration and in special effects for movies and stage productions.


Physical properties

Carbon (IV) oxide, also known as carbon dioxide, is a colorless, odorless gas with the chemical formula CO2. Here are some of its physical properties:

  1. State: Carbon dioxide is a gas at room temperature and standard atmospheric pressure. It can also exist in a solid form called dry ice, which is used in many industrial applications.
  2. Density: The density of carbon dioxide gas is about 1.98 kg/m3 at standard conditions of temperature and pressure (STP).
  3. Solubility: Carbon dioxide is highly soluble in water, and it can also dissolve in other polar solvents like ethanol and acetone. The solubility of carbon dioxide in water increases with decreasing temperature and increasing pressure.
  4. Boiling and melting point: Carbon dioxide does not have a boiling point at atmospheric pressure, it sublimates directly from a solid to a gas. Its melting point is -78.5°C.
  5. Molecular weight: The molecular weight of carbon dioxide is 44.01 g/mol.
  6. Viscosity: Carbon dioxide has a low viscosity, meaning that it flows easily.
  7. Odor: Carbon dioxide is odorless and tasteless.
  8. Color: Carbon dioxide is a colorless gas.
  9. pH: Carbon dioxide can react with water to form carbonic acid, which lowers the pH of water.
  10. Flammability: Carbon dioxide is not flammable, but it can act as a fire suppressant by displacing oxygen in a fire.


Laboratory preparation

Carbon dioxide (CO2) is the most common form of carbon (IV) oxide. Here are a few ways in which carbon dioxide can be prepared in the laboratory:

1) Reaction of acid and carbonate: Carbon dioxide is produced when an acid reacts with a carbonate. The general equation for the reaction is:acid + carbonate → salt + water + carbon dioxide

For example, when hydrochloric acid (HCl) reacts with calcium carbonate (CaCO3), the following reaction takes place:

2HCl + CaCO3 → CaCl2 + H2O + CO2


2) Combustion of carbon-containing compounds: The combustion of carbon-containing compounds such as methane (CH4) or ethane (C2H6) produces carbon dioxide. The general equation for the combustion of hydrocarbons is:

hydrocarbon + oxygen → carbon dioxide + water

For example, when methane is burned in the presence of oxygen, the following reaction occurs:

CH4 + 2O2 → CO2 + 2H2O


3) Reaction of metal and acid: Carbon dioxide is also produced when a metal reacts with an acid. The general equation for the reaction is:

metal + acid → salt + hydrogen gas + carbon dioxide

For example, when magnesium (Mg) reacts with hydrochloric acid (HCl), the following reaction takes place:

Mg + 2HCl → MgCl2 + H2 + CO2


4) Decarboxylation of carboxylic acids: Carbon dioxide is produced when a carboxylic acid undergoes decarboxylation, which involves the removal of a carbon atom in the form of CO2. The general equation for decarboxylation is:

carboxylic acid → carbon dioxide + an alkane

For example, when acetic acid (CH3COOH) undergoes decarboxylation, the following reaction occurs:



These are some of the methods used to prepare carbon dioxide in the laboratory.


Chemical properties

Carbon dioxide (CO2) is a colorless gas that has several important chemical properties, including:

1) Acidic: Carbon dioxide reacts with water to form carbonic acid, which is a weak acid that can ionize to produce hydrogen ions (H+) and bicarbonate ions (HCO3-):

CO2 + H2O ↔ H2CO3 H2CO3 ↔ H+ + HCO3-

This reaction is important in controlling the pH of water bodies, such as the oceans, as well as in regulating the pH of blood in animals.


2) Oxidizing: Carbon dioxide is a good oxidizing agent, meaning it can accept electrons from other substances. For example, carbon dioxide can oxidize metals like magnesium to form metal oxides and carbon:

2Mg + CO2 → 2MgO + C

This reaction is commonly used in fireworks to produce a bright white light.


3) Non-flammable: Carbon dioxide is non-flammable and does not support combustion. In fact, it can be used as a fire extinguisher by displacing oxygen, which is necessary for combustion, from the area around the fire.


4) Soluble in water: Carbon dioxide is soluble in water, forming carbonic acid. This property is important for the regulation of carbon dioxide levels in the atmosphere and in the oceans.


5) Forms carbonate salts: Carbon dioxide reacts with metal oxides and hydroxides to form carbonate salts, such as calcium carbonate (CaCO3):

CO2 + CaO → CaCO3

This reaction is important in the formation of limestone and other sedimentary rocks.


Uses of CO2

Carbon dioxide (CO2) is an important gas in chemistry with many uses. Some of its uses include:

  1. As a reactant: Carbon dioxide is used as a reactant in a variety of chemical reactions. For example, it is used in the production of urea, which is an important industrial chemical. It is also used in the production of certain polymers and plastics.
  2. As a solvent: Carbon dioxide is used as a solvent for certain chemical reactions, particularly those involving organic compounds. It is an attractive solvent due to its relatively low cost, safety, and environmentally friendly properties.
  3. As a refrigerant: Carbon dioxide is used as a refrigerant in some industrial and commercial applications. It is an environmentally friendly alternative to many other refrigerants that are more harmful to the environment.
  4. As a fire extinguisher: Carbon dioxide is used as a fire extinguisher in many applications. When released, it displaces oxygen, suffocating the fire. It is commonly used in places where water-based extinguishers cannot be used, such as electrical fires.
  5. As a greenhouse gas: Carbon dioxide is an important greenhouse gas that helps to regulate the Earth’s temperature. However, excessive emissions of carbon dioxide from human activities, such as burning fossil fuels, are contributing to global climate change.


Test for carbon (IV) oxides

There are different tests that can be carried out to identify the presence of carbon (IV) oxide (CO2). Here are some common tests and their corresponding chemical equations:

1) Limewater test: When CO2 is passed through limewater (calcium hydroxide solution), a white precipitate of calcium carbonate is formed.

Ca(OH)2 + CO2 → CaCO3 + H2O


2) Bicarbonate test: CO2 reacts with sodium bicarbonate solution to form sodium carbonate and water, releasing carbon dioxide gas.

NaHCO3 + HCl → NaCl + CO2 + H2O


3) Burning splint test: CO2 extinguishes a burning splint, as it does not support combustion.

C6H12O6 + 6O2 → 6CO2 + 6H2O + heat


4) Lime water and barium chloride test: When CO2 reacts with barium chloride and limewater, it forms a white precipitate of barium carbonate.

BaCl2 + CO2 + H2O → BaCO3 + 2HCl


5) Gas syringe method: In this test, CO2 is allowed to react with a metal carbonate, such as calcium carbonate, to produce carbon dioxide gas, which is collected in a gas syringe.

CaCO3 + 2HCl → CaCl2 + CO2 + H2O

Overall, these tests can be used to identify the presence of carbon (IV) oxide in various settings, from laboratory experiments to detecting it in the air.