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 slightly salty, alkaline taste resembling that of washing soda. The
natural mineral form is nahcolite. It is a component of the mineral natron and is found
dissolved in many mineral springs. It is among the food additives encoded by European Union,
identified by the initials E 500. Since it has long been known and is widely used, the
salt has many related names such as baking soda, bread soda, cooking soda, and bicarbonate
of soda. In colloquial usage, its name is sometimes shortened to sodium bicarb, bicarb
soda, simply bicarb, or even bica. 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. Sodium bicarbonate is usually
called baking soda in general terms.
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 carbonate, also known as soda
ash. 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.
This compound, referred to as saleratus, is mentioned in the famous novel Captains Courageous
by Rudyard Kipling as being used extensively in the 1800s in commercial fishing to prevent
freshly-caught fish from spoiling. Production
NaHCO3 is mainly prepared by the Solvay process, which is the reaction of sodium chloride,
ammonia, and carbon dioxide in water. Calcium carbonate is used as the source of CO2 and
the resultant calcium oxide is used to recover the ammonia from the ammonium chloride. The
product shows a low purity. Pure product is obtained from sodium carbonate, water and
carbon dioxide as reported in one of the following reactions. It is produced on the scale of
about 100,000 tonnes/year. 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
are found in the Eocene-age 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 that is pumped
through the nahcolite beds and reconstituted through a natural cooling crystallization
process. 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 → H
2CO 3 + 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 produce
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, producing sodium acetate, water, and carbon
dioxide: 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 CO
2. This reaction is used to test for the presence of carboxylic groups in protein.
Thermal decomposition Above 50 °C, sodium bicarbonate gradually
decomposes into sodium carbonate, water and carbon dioxide. The conversion is fast at
200 °C: 2 NaHCO3 → Na2CO3 + H2O + CO2
Most bicarbonates undergo this dehydration reaction. Further heating converts the carbonate
into the oxide: Na2CO3 → Na2O + CO2
These conversions are relevant to the use of NaHCO3 as a fire-suppression agent in some
dry powder fire extinguishers. Applications
Sodium bicarbonate is used in a process for removing paint and corrosion called sodablasting;
the process is particularly suitable for cleaning aluminium panels which can be distorted by
other types of abrasive. It can be administered to pools, spas, and garden ponds to raise
pH levels. It has weak disinfectant properties, and it may be an effective fungicide against
some organisms. Because baking soda will absorb musty smells, it has become a reliable method
for used-book sellers when making books less malodorous.
Fire extinguisher Sodium bicarbonate can be used to extinguish
small grease or electrical fires by being thrown over the fire. However, it should not
be applied to fires in deep fryers, as it may cause the grease to splatter. 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.
Cooking
Sodium bicarbonate, referred to as "baking soda" is primarily used in cooking, as a leavening
agent. It reacts with acidic components in batters, releasing carbon dioxide, which causes
expansion of the batter and forms the characteristic texture and grain in pancakes, cakes, quick
breads, soda bread, and other baked and fried foods. 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. Many forms of baking powder contain sodium bicarbonate
combined with calcium acid phosphate, sodium aluminum sulphate or cream of tartar.
Sodium bicarbonate was sometimes used in cooking vegetables, to make them softer, although
this has gone out of fashion, as most people now prefer firmer vegetables. However, it
is still used in Asian and Latin American cuisine to tenderise meats. Baking soda may
react with acids in food, including Vitamin C. It is also used in breadings such as for
fried foods to enhance crispness. Heat causes sodium bicarbonate to act as a
raising agent by releasing carbon dioxide when used in baking. The carbon dioxide production
starts at temperatures above 80 °C. Since the reaction does not occur at room temperature,
mixtures can be allowed to stand without rising until they are heated in the oven.
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. Also, sodium bicarbonate powder may be used
to smother a small fire, as heating of sodium bicarbonate releases carbon dioxide.
A wide variety of applications follows from its neutralization properties, including reducing
the spread of white phosphorus from incendiary bullets inside an afflicted soldier's wounds.
Medical uses Sodium bicarbonate mixed with water can be
used as an antacid to treat acid indigestion and heartburn. It is used as the medicinal
ingredient in gripe water for infants. Intravenous sodium bicarbonate is an aqueous
solution that is sometimes used for cases of acidosis, or when there are insufficient
sodium or bicarbonate ions in the blood. 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 markedly low. It is used for treatment of hyperkalemia.
Since sodium bicarbonate can cause alkalosis, it is sometimes used 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. It can also be applied topically
as a paste, with three parts baking soda to one part water, to relieve some kinds of insect
bites and stings. 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 consuming a high-calcium or dairy-rich diet, calcium supplements, or
calcium-containing antacids such as calcium carbonate, the use of sodium bicarbonate can
cause milk-alkali syndrome, which can result in metastatic calcification, kidney stones,
and kidney failure. Sodium bicarbonate can be used to treat an
allergic reaction to plants such as poison -ivy -oak or -sumac to relieve some of the
associated itching. Bicarbonate of soda can also be useful in
removing splinters from the skin. Some alternative practitioners, such as Tullio
Simoncini, have promoted baking soda as a cancer cure, which the American Cancer Society
has warned against due to both its unproven effectiveness and potential danger in use.
Personal hygiene Toothpaste containing sodium bicarbonate has
in several studies shown to have a better whitening and plaque removal effect than toothpastes
without it. Sodium bicarbonate is also used as an ingredient
in some mouthwashes. It has anti-caries and abrasive properties. It works as a mechanical
cleanser on the teeth and gums, neutralizes the production of acid in the mouth and also
acts as an antiseptic to help prevent infections. Sodium bicarbonate in combination with other
ingredients can be used to make a dry or wet deodorant. It may also be used as a shampoo.
Sodium bicarbonate may be used as a buffering agent, combined with table salt, when creating
a solution for nasal irrigation. In sports
Small amounts of sodium bicarbonate have been shown to be useful as a supplement for athletes
in speed-based events, like middle distance running, lasting from about one to seven minutes.
However, overdose is a serious risk because sodium bicarbonate is slightly toxic; gastrointestinal
irritation is of particular concern. Additionally, this practice causes a significant increase
in dietary sodium. As a cleaning agent
A paste from baking soda can be very effective when used in cleaning and scrubbing. For cleaning
aluminium objects, the use of sodium bicarbonate is 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.
A paste of sodium bicarbonate and water is useful in removing surface rust as the rust
forms a water soluble compound when in a concentrated alkaline solution. Cold water should be used
as hot water solutions can corrode steel. Baking soda is commonly added to washing machines
as a replacement for softener and to remove odors from clothes. Sodium bicarbonate is
also effective in removing heavy tea and coffee stains from cups when diluted with warm water.
During the Manhattan Project to develop the atomic bomb in the early 1940s, many scientists
investigated the toxic properties of uranium. They found that uranium oxides stick very
well to cotton cloth, but did not wash out with soap or laundry detergent. The uranium
would wash out with a 2% solution of sodium bicarbonate. Clothing can become contaminated
with depleted uranium dust and normal laundering will not remove it. Those at risk of DU dust
exposure should have their clothing washed with baking soda of baking soda in 2 gallons
of water). As a biopesticide
Sodium bicarbonate can be an effective way of controlling fungus growth, and in the United
States is registered by the Environmental Protection Agency as a biopesticide.
Cattle feed supplements Sodium bicarbonate is sold as a cattle feed
supplement, in particular as a buffering agent for the rumen.
In popular culture Film
Sodium bicarbonate, as 'bicarbonate of soda', was a frequent source of punch lines for Groucho
Marx in Marx brothers movies. In Duck Soup, Marx plays the leader of a nation at war.
In one scene, he receives a message from the battlefield that his general is reporting
a gas attack, and Groucho tells his aide, "Tell him to take a teaspoonful of bicarbonate
of soda and a half a glass of water." In A Night at the Opera, Groucho's character addresses
the opening night crowd at an opera by saying of the lead tenor, "Signor Lassparri comes
from a very famous family. His mother was a well-known bass singer. His father was the
first man to stuff spaghetti with bicarbonate of soda, thus causing and curing indigestion
at the same time." Difference between baking soda and baking
powder In comparison to baking powder, baking soda
is more alkaline and requires an acid to avoid the metallic taste when the chemical change
creates sodium carbonate. Baking powder, on the other hand, contains baking soda, a powdered
acid and cornstarch. In scientific terms, baking soda is a pure substance; baking powder
is a mixture. If baking soda is used in baking, something
acidic must be added to avoid the metallic taste of sodium carbonate; but with baking
powder, non-acid ingredients such as whole milk or Dutch-processed cocoa must be added
to avoid the over-flavouring of acidic taste. See also
Carbonic acid Irish soda bread
List of ineffective cancer treatments List of minerals
Nahcolite Natron
Natrona Trona
Washing soda
References
Further reading Bishop, D; Edge, J; Davis, C; Goodman, C.
"Induced metabolic alkalosis affects muscle metabolism and repeated-sprint ability". Medicine
and science in sports and exercise 36: 807–13. doi:10.1249/01.MSS.0000126392.20025.17. ISSN 0195-9131.
PMID 15126714. David R. Lide, ed.. CRC Handbook of Chemistry
and Physics. Boca Raton, FL: CRC Press. ISBN 0-8493-0484-9. External links
International Chemical Safety Card 1044 Differences between Baking Soda and Baking
Powder