Sodium_bicarbonate

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Sodium bicarbonate

Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula NaHCO₃. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slight alkaline taste resembling that of washing soda (sodium carbonate). It is a component of the mineral natron and is found dissolved in many mineral springs. The natural mineral form is known as nahcolite. It is also produced artificially.

Since it has long been known and is widely used, the salt has many related names such as baking soda, bread soda, cooking soda, bicarbonate of soda. Colloquially, its name is shortened to sodium bicarb. The word saleratus, from Latin sal æratus meaning "aerated salt", was widely used in the 19th century for both sodium bicarbonate and potassium bicarbonate. The term has now fallen out of common usage.

History

The ancient Egyptians used natural deposits of natron, a mixture consisting mostly of sodium carbonate decahydrate and sodium bicarbonate. The natron was used as a cleansing agent like soap.

In 1791, a French chemist produced sodium bicarbonate as we know it today. But it was only in 1846 that two New York bakers, John Dwight and Austin Church, developed the process of making baking soda from sodium carbonate and carbon dioxide. Each started a company, and the two companies later merged to form Church & Dwight, the makers of Arm & Hammer baking soda.

Production

NaHCO₃ is mainly prepared by the Solvay process, which is the reaction of calcium carbonate, sodium chloride, ammonia, and carbon dioxide in water. It is produced on the scale of about 100,000 ton/year (as of 2001).

NaHCO₃ may be obtained by the reaction of carbon dioxide with an aqueous solution of sodium hydroxide. The initial reaction produces sodium carbonate:

CO₂ + 2NaOH → Na₂CO₃ + H₂O

Further addition of carbon dioxide produces sodium bicarbonate, which at sufficiently high concentration will precipitate out of solution:

Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃

Commercial quantities of baking soda are also produced by a similar method: soda ash, mined in the form of the ore trona, is dissolved in water and treated with carbon dioxide. Sodium bicarbonate precipitates as a solid from this method:

Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃

Mining

Naturally occuring deposits of nahcolite (NaHCO₃) are found in the Eocene-age (55.8 ± 0.2 - 33.9 ± 0.1 Ma) Green River Formation, Piceance Creek Basin in Colorado. Nahcolite was deposited as beds during periods of high evaporation in the basin. It is commercially mined using in-situ leach techniques involving dissolution of the nahcolite by heated water which is pumped through the nahcolite beds and reconstituted through a natural cooling crystallization process. Natural Soda, Inc., the only North American processor of natural sodium bicarbonate is owned by AmerAlia (AALA) and The Sentient Group. The operation is located 54 miles northwest of Rifle, Colorado.

Chemistry

Sodium bicarbonate is an amphoteric compound. Aqueous solutions are mildly alkaline:

HCO₃^- + H₂O → H₂CO₃ + OH^-

Sodium bicarbonate can be used as a wash to remove any acidic impurities from a "crude" liquid, producing a more pure sample. Reaction of sodium bicarbonate and an acid to give a salt and carbonic acid, which readily decomposes to carbon dioxide and water:

NaHCO₃ + HCl → NaCl + H₂CO₃

H₂CO₃ → H₂O + CO₂ (gas)

Reaction of sodium bicarbonate and acetic acid:

NaHCO₃ + CH₃COOH → CH₃COONa + H₂O + CO₂ (gas)

Sodium bicarbonate reacts with bases:

NaHCO₃ + NaOH → Na₂CO₃ + H₂O

Thermal decomposition

Above 60 °C, it gradually decomposes into sodium carbonate, water and carbon dioxide. The conversion is fast at 200 °C:

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Most bicarbonates undergo this dehydration reaction. Further heating converts the carbonate into the oxide (at around 1000 °C):

Na₂CO₃ → Na₂O + CO₂

These conversions are relevant to the use of NaHCO₃ as a fire-suppression agent ("BC powder") in some dry powder fire extinguishers.

Applications

Cooking

Sodium bicarbonate is primarily used in cooking (baking) where it reacts with other components to release carbon dioxide, that helps dough "rise". The acidic compounds that induce this reaction include phosphates, cream of tartar, lemon juice, yogurt, buttermilk, cocoa, vinegar, etc. Hence, sodium bicarbonate can be substituted for baking powder provided sufficient acid reagent is also added to the recipe. Many forms of baking powder contain sodium bicarbonate combined with one or more acidic phosphates or cream of tartar.

Neutralization of acids and bases

Many laboratories keep a bottle of sodium bicarbonate powder within easy reach, because sodium bicarbonate is amphoteric, reacting with acids and bases. (See Chemistry) Furthermore, as it is relatively innocuous in most situations, there is no harm in using excess sodium bicarbonate. Lastly, sodium bicarbonate powder may be used to smother a small fire.

A wide variety of applications follows from its neutralization properties, including ameliorating the effects of white phosphorus in incendiary bullets from spreading inside an afflicted soldier's wounds. Sodium bicarbonate can be added as a simple solution for raising the pH balance of water that has a high level of chlorine, such as in swimming pools and aquariums.

Medical uses

Sodium bicarbonate is used as an antacid to treat acid indigestion and heartburn An aqueous solution is administered intravenously for cases of acidosis, or when there is insufficient sodium or bicarbonate ions in the blood. This compound has also been used as for patients who have had a ureterosigmoidostomy.

Adverse reactions to emergency administration include congestive heart failure, with edema secondary to sodium overload, and the metabolic complication of hyperosmolarity, metabolic alkalosis, and hypernatremia.

Sodium bicarbonate may also be used as an anti-fungal for dandruff caused by fungus.

As a cleaning agent

A paste from baking soda can be very effective when used in cleaning and scrubbing.
For cleaning of aluminium objects it is to be discouraged as it attacks the thin unreactive protective oxide layer of this otherwise very reactive metal.
A solution in warm water will remove the tarnish from silver when the silver is in contact with a piece of aluminium foil
Has been used for many years informally as a tooth whitening agent.

Miscellaneous

It has been discovered that used under the right circumstances, baking soda can be used for lamination, if applied correctly.
Sodium bicarbonate is used in BC Dry Chemical fire extinguishers as an alternative to the more corrosive ammonium phosphate in ABC extinguishers. The alkali nature of sodium bicarbonate makes it the only dry chemical agent, besides Purple-K, that was allowed for use on commercial deep fat fryers. The agent has a mild saponification effect on the grease, which forms a smothering soapy foam. Dry Chemicals have since fallen out of favor for kitchen fires as they have no cooling effect compared to the extremely effective wet chemical agents specifically designed for such hazards.
It is used in a process for cleaning paint called sodablasting.
It can be used as a carbon sequestration agent to trap carbon dioxide greenhouse gas emissions in solid form, as one potential tool against global warming.
It can be administered to spas and garden ponds to raise pH levels.
It can be used to remove odors from books. It is a tried-and-true method of used booksellers. The baking soda will absorb the musty smell, leaving the books less stinky.