inorganic chemistry, bicarbonate ( IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonationof carbonic acid.
Bicarbonate serves a crucial biochemical role in the physiological
pHbuffering system. [http://www.biology.arizona.edu/biochemistry/problem_sets/medph/intro.html http://www.biology.arizona.edu/biochemistry/problem_sets/medph/intro.html]
Biology.arizona.edu - October 2006. "Clinical correlates of pH levels: bicarbonate as a buffer."]
The bicarbonate ion (hydrogen carbonate) is an
anionwith the empirical formulaHCO3− and a molecular mass of 61.01 daltons; it consists of one central carbon atomsurrounded by three oxygen atoms in a trigonal planararrangement, with a hydrogen atom attached to one of the oxygens. The bicarbonate ion carries a negative one formal chargeand is the conjugate base of carbonic acid, H2CO3; it is the conjugate acidof CO32−, the carbonateion as shown by these equilibrium reactions.
CO32− +2 H2O ⇋ HCO3− + H2O + OH− ⇋ H2CO3 +2 OH−
H2CO3 +2 H2O ⇋ HCO3− + H3O+ + H2O ⇋ CO32− +2 H3O+
A bicarbonate salt forms when a positively charged ion attaches to the negatively charged oxygen atoms of the ion, forming an ionic compound. Many bicarbonates are soluble in
waterat standard temperature and pressure, particularly sodium bicarbonateand magnesium bicarbonate; both of these substances contribute to total dissolved solids, a common parameter for assessing water quality.
Bicarbonate is an
alkaline, and a vital component of the pHbuffering system of the body (maintaining acid-base homeostasis). 86%-90% of CO2 in the body is converted into carbonic acid(H2CO3), which can quickly turn into bicarbonate (HCO3−).
With carbonic acid as the central intermediate species, bicarbonate, in conjunction with water,
hydrogen ions, and carbon dioxideforms this buffering system which is maintained at the volatile equilibrium required to provide prompt resistance to drastic pH changes in both the acidic and basic directions. This is especially important for protecting tissues of the central nervous system, where pH changes too far outside of the normal range in either direction could prove disastrous. (See acidosis, or alkalosis.)
Bicarbonate also acts to regulate pH in the small intestine. It is released from the
pancreasin response to the hormone secretinto neutralize the acid chyme entering the duodenum from the stomach [ Berne & Levy, Principles of Physiology ]
The most common salt of the bicarbonate ion is
sodium bicarbonate, NaHCO3, which is used as baking soda. When exposed to an acidsuch as acetic acid( vinegar), sodium bicarbonate releases carbon dioxide. This is used as a leavening agentin baking.
The flow of bicarbonate ions from rocks weathered by the carbonic acid in rainwater is an important part of the
Bicarbonate also serves in the digestive system. It raises the internal pH of the stomach, after highly acidic digestive juices have finished in their digestion of food.
Ammonium bicarbonateis used in digestive biscuitmanufacture.
diagnostic medicine, the blood valueof bicarbonate is one of several indicators of the state of acid-base physiologyin the body.
The parameter "Standard bicarbonate concentration" (SBCe) is the bicarbonate concentration in the blood at a CO2 of 5.33kPa, full oxygen saturation and 37 degrees
Celsius. [ [http://www.nda.ox.ac.uk/wfsa/html/u13/u1312_03.htm Acid Base Balance (page 3)] ]
Arterial blood gas
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