sodium bicarbonate

Sodium bicarbonate
IUPAC name	Sodium hydrogen carbonate
Other names	Sodium bicarbonate Bicarbonate of soda Baking soda Sodium hydrogencarbonate Nahcolite
Identifiers
CAS number	144-55-8 Y
PubChem	516892
RTECS number	VZ0950000
ChemSpider ID	8609
Properties
Molecular formula	CHNaO3
Molar mass	84.01 g mol−1
Appearance	white crystalline solid
Odor	odorless
Density	2.173 g/cm3
Melting point	270 °C (decomp)
Solubility in water	7.8 g/100 mL (18 °C) 10 g/100 mL (20 °C)
Solubility	insoluble in alcohol, ether
Acidity (pKa)	10.3
Refractive index (nD)	1.3344
Hazards
MSDS	External MSDS
EU Index	Not listed
NFPA 704	0 1 0
Flash point	Non-flammable
LD50	4220 mg/kg
Related compounds
Other anions	Sodium carbonate
Other cations	Potassium bicarbonate Ammonium bicarbonate
Related compounds	Sodium bisulfate Sodium hydrogen phosphate
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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, bicarb soda, or simply 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, Nicolas Leblanc, produced sodium bicarbonate as we know it today. In 1846 two New York bakers, John Dwight and Austin Church, established the first factory to develop baking soda from sodium carbonate and carbon dioxide.^[1]

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).^[2]

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

CO₂ + 2 NaOH → Na₂CO₃ + H₂O

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

Na₂CO₃ + CO₂ + H₂O → 2 NaHCO₃

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 → 2 NaHCO₃

Mining

Naturally occurring deposits of nahcolite (NaHCO₃) are found in the Eocene-age (55.8 ± 0.2 - 33.9 ± 0.1 Ma) Green River Formation, Piceance 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. The Natural Soda facility has changed ownership several times over the last decade, it proving difficult to turn a profit. All other North American producers base their production of sodium bicarbonate on trona found in the Green River Formation of Wyoming.

Chemistry

Sodium bicarbonate is an amphoteric compound. Aqueous solutions are mildly alkaline due to the formation of carbonic acid and hydroxide ion:

HCO−3 + H₂O → H₂CO₃ + OH⁻

Sodium bicarbonate can be used as a wash to remove any acidic impurities from a "crude" liquid, producing a purer 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 (g)

Sodium bicarbonate reacts with acetic acid (CH₃COOH) to form sodium acetate:

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

Sodium bicarbonate reacts with bases such as sodium hydroxide to form carbonates:

NaHCO₃ + NaOH → Na₂CO₃ + H₂O

Sodium bicarbonate reacts with carboxyl groups in proteins to give a brisk effervescence from the formation of CO₂. This reaction is used to test for the presence of carboxylic groups in protein.

Thermal decomposition

Above 70 °C, sodium bicarbonate gradually decomposes into sodium carbonate, water and carbon dioxide. The conversion is fast at 250 °C:^{[citation needed]}

2 NaHCO₃ → 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. Sodium bicarbonate can be substituted for baking powder provided sufficient acid reagent is also added to the recipe.^[3] Many forms of baking powder contain sodium bicarbonate combined with one or more acidic phosphates (especially good) or cream of tartar. Can also be used for softening peas (⅛ tsp. per pint of water and bring to boil for one hour)

Thermal decomposition causes sodium bicarbonate alone to act as a raising agent by releasing carbon dioxide at baking temperatures. The mixture for cakes using this method can be allowed to stand before baking without any premature release of carbon dioxide.

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. 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. ^[4]

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.^[5] Sodium bicarbonate can be added as a simple solution for raising the pH balance of water (increasing total alkalinity) where high levels of chlorine (2-5 ppm) are present as in swimming pools and aquariums.^[6]

Medical uses

Sodium bicarbonate is used in an aqueous solution as an antacid taken orally to treat acid indigestion and heartburn.^[7] It may also be used in an oral form to treat chronic forms of metabolic acidosis such as chronic renal failure and renal tubular acidosis. Sodium bicarbonate may also be useful in urinary alkalinization for the treatment of aspirin overdose and uric acid renal stones.

An aqueous solution is sometimes administered intravenously for cases of acidosis, or when there are insufficient sodium or bicarbonate ions in the blood. ^[8]In cases of respiratory acidosis, the infused bicarbonate ion drives the carbonic acid/bicarbonate buffer of plasma to the left and, thus, raises the pH. It is for this reason that sodium bicarbonate is used in medically-supervised cardiopulmonary resuscitation. Infusion of bicarbonate is indicated only when the blood pH is marked (<7.1-7.0) low.^[9]

It is used as well for treatment of hyperkalemia. Since sodium bicarbonate can cause alkalosis, it is sometimes used in to treat aspirin overdoses. Aspirin requires an acidic environment for proper absorption, and the basic environment diminishes aspirin absorption in the case of an overdose. Sodium bicarbonate has also been used in the treatment of tricyclic antidepressant overdose.^[10] It can also be applied topically as a paste, with three parts baking soda to one part water, to relieve insect bites. ^[11]

Adverse reactions to the administration of sodium bicarbonate can include metabolic alkalosis, edema due to sodium overload, congestive heart failure, hyperosmolar syndrome, hypervolemic hypernatremia, and hypertension due to increased sodium. In patients who consume a high calcium or dairy-rich diet, calcium supplements, or calcium-containing antacids such as calcium carbonate (e.g., Tums), the use of sodium bicarbonate can cause milk-alkali syndrome, which can result in metastatic calcification, kidney stones, and kidney failure.

Sodium bicarbonate is also used as an ingredient in some mouthwashes. It works as a mechanical cleanser on the teeth and gums, neutralizes the production of acid in the mouth and also as an antiseptic to help prevent infections occurring.

Personal hygiene

A paste made from sodium bicarbonate and a 3% hydrogen peroxide solution can be used as an alternative to commercial non-fluoride toothpastes, and sodium bicarbonate in combination with other ingredients can be used to make a dry or wet deodorant. Sodium bicarbonate is a common ingredient in alternative and natural brands of toothpaste and deodorant. It can be used as a treatment for dandruff due to its anti-fungal properties.^{[citation needed]}

Soda loading

Small amounts of sodium bicarbonate have been shown to be useful as a supplement for endurance athletes,^[12] but overdose is a serious risk.^[13]

As a cleaning agent

A paste from baking soda can be very effective when used in cleaning and scrubbing.^[14] For cleaning aluminium objects, sodium bicarbonate 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.^[15]

Baking soda is commonly added to the rinse cycles of washing machines (together with the detergent) as a replacement for softener and also to remove odors. Sodium bicarbonate is also effective in removing heavy tea and coffee stains from cups when diluted with warm water.

Miscellaneous

Sodium bicarbonate can be used to extinguish small grease or electrical fires by being poured or dumped over the fire.^[4] However, it should not be poured or dumped onto fires in deep fryers as it may cause the grease to splatter.^[4] 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 used in large scale fire suppression systems installed in commercial kitchens. Because it can act as an alkali, the agent has a mild saponification effect on hot 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.^{[citation needed]}

Sodium bicarbonate is used in a process for cleaning paint called sodablasting. It can be administered to pools, spas, and garden ponds to raise pH levels.^[16] It has disinfectant and antiseptic properties,^[17] and it may be an effective fungicide against some organisms.^[18]

Because it can be used to absorb odors, it is a tried-and-true method of used booksellers. The baking soda will absorb the musty smell, leaving the books less odorous.^[19]

See also

• Carbonic acid
• Baking powder
• List of minerals
• Nahcolite
• Natron
• Natrona (disambiguation)
• Trona

References

Further reading

• Bishop, D; Edge, J; Davis, C; Goodman, C (May 2004). "Induced metabolic alkalosis affects muscle metabolism and repeated-sprint ability.". Medicine and science in sports and exercise 36 (5): 807–13. ISSN 0195-9131. PMID 15126714. 

External links

Wikimedia Commons has media related to: Sodium bicarbonate

Wikibooks Cookbook has a recipe/module on Baking soda

• International Chemical Safety Card 1044
• Differences between Baking Soda and Baking Powder