Carbon dioxide

Carbon dioxide, one of the more common gasses in earth's atmosphere, is a molecule containing one carbon atom and two oxygen atoms. It is related to carbon monoxide.

Properties

Chemical

Carbon dioxide is soluble in water, making carbonic acid. This is not very stable, existing as an equilibrium between carbonic acid and carbon dioxide/water, and cannot be concentrated.

CO₂ + H₂O ⇌ H₂CO₃

However, this limited temporary solubility can still be taken advantage of in converting hydroxides to carbonates, such as in the treatment of limewater with carbon dioxide to precipitate calcium carbonate. Carbon dioxide can also be used as an acid to oxidize some species, such as the oxidation of potassium manganate to permanganate.

Carbon dioxide is released in many chemical reactions, usually because of the acidification of a carbonate.

Magnesium, titanium, potassium, and other reactive metals will reduce carbon dioxide to carbon.

Physical

Carbon dioxide is a colorless, odorless gas. It cannot be isolated in liquid form at room temperature and atmospheric pressure, but sublimes. In solid form, it is called "dry ice", and used for chilling experiments. Carbon dioxide is a relatively cheap inert gas, and although for most chemicals it may cause reaction, it is a good storage gas for most reactive metals, except the metals from the s-block and lanthanides.

Availability

Carbon dioxide is available by generation from common materials (like sodium bicarbonate), from the air, in canisters, or in the form of dry ice, which may be sold at grocery stores and wedding planner entities. Dry ice may also be produced by placing the end of a fire extinguisher(which often contains carbon dioxide) into a bag and releasing the pressurized gas. Fresh dry ice is formed within the confines of the bag.

Preparation

Acidification of a carbonate or bicarbonate releases carbon dioxide, which is a cheap way to generate it. Burning organic materials will also generate carbon dioxide, but will also generate soot, water vapor, formaldehyde, aromatic compounds, so it's best to bubble the resulting smoke into a liquid or an adsorption column that will remove the contaminants.

Projects

• Cooling baths
• Carbonates
• Make calcium bicarbonate solution
• Gas nozzles
• Inert atmosphere (not useful for several compounds)

Handling

Safety

Carbon dioxide is not directly poisonous, like carbon monoxide, but it will lower the pH of the blood to dangerous levels if it is inhaled in excess. Carbon dioxide

The extreme cold of solid carbon dioxide can immediately cause reverse thermal burns if it comes into contact with skin.

Storage

Compressed carbon dioxide should be stored in cold places, away from heat. Dry ice should be stored in dewars, as well away from heat sources. Storage should not be done over long periods of time. Both forms should not be stored in chambers lower than ground level, as CO₂ may build-up and pose an asphyxiation hazard.

Disposal

Carbon dioxide can be released in open air. Avoid releasing it in an enclosed space.

References

Relevant Sciencemadness threads

• Co2 in beverages?