Bicarbonate

For baking soda, see sodium bicarbonate. For the programming principle, see Tim Toady Bicarbonate.

"Hydrogen carbonate" redirects here. For the oxoacid, see carbonic acid.

Bicarbonate
Names


Systematic IUPAC name Hydroxidodioxidocarbonate(1−)^[1]
Other names Hydrogencarbonate^[1]
Identifiers
CAS Number	71-52-3^Y
3D model (Jmol)	Interactive image
3DMet	B00080
Beilstein Reference	3903504
ChEBI	CHEBI:17544^Y
ChEMBL	ChEMBL363707^Y
ChemSpider	749^Y
Gmelin Reference	49249
KEGG	C00288^Y
PubChem	769
UNII	HN1ZRA3Q20^Y
InChI InChI=1S/CH2O3/c2-1(3)4/h(H2,2,3,4)/p-1^Y Key: BVKZGUZCCUSVTD-UHFFFAOYSA-M^Y
SMILES OC([O-])=O
Properties
Chemical formula	HCO− 3
Molar mass	61.0168 g mol⁻¹
log P	−0.82
Acidity (pK_a)	10.3 (Conjugate acid of carbonate)
Basicity (pK_b)	7.7 (Conjugate base of carbonic acid)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogen carbonate^[2]) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula H C O−
3.

Bicarbonate serves a crucial biochemical role in the physiological pH buffering system.^[3]

The term "bicarbonate" was coined in 1814 by the English chemist William Hyde Wollaston.^[4] The prefix "bi" in "bicarbonate" comes from an outdated naming system and is based on the observation that there is twice as much carbonate (CO2−
3) per sodium ion in sodium bicarbonate (NaHCO₃) and other bicarbonates than in sodium carbonate (Na₂CO₃) and other carbonates.^[5] The name lives on as a trivial name.

Chemical properties

The bicarbonate ion (hydrogencarbonate ion) is an anion with the empirical formula HCO−
3 and a molecular mass of 61.01 daltons; it consists of one central carbon atom surrounded by three oxygen atoms in a trigonal planar arrangement, with a hydrogen atom attached to one of the oxygens. It is isoelectronic with nitric acid HNO
3. The bicarbonate ion carries a negative one formal charge and is the conjugate base of carbonic acid H
2CO
3; at the same time, it is the conjugate acid of CO2−
3, the carbonate ion, as shown by these equilibrium reactions:

CO2−
3 + 2 H₂O ⇌ HCO−
3 + H₂O + OH⁻ ⇌ H₂CO₃ + 2 OH⁻

H₂CO₃ + 2 H₂O ⇌ HCO−
3 + H₃O⁺ + H₂O ⇌ CO2−
3 + 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 water at standard temperature and pressure; in particular, sodium bicarbonate contributes to total dissolved solids, a common parameter for assessing water quality.

Physiological role

CO₂ produced as a waste product of the oxidation of sugars in the mitochondria reacts with water to form H₂CO₃, which is in equilibrium with the cation H⁺ and anion HCO₃⁻. It is then carried to the lung, where the reverse reaction occurs and CO₂ gas is released. In the kidney (left), cells (green) lining the proximal tubule conserve bicarbonate by transporting it from the glomerular filtrate in the lumen (yellow) of the nephron back into the blood (red). The exact stoichiometry in the kidney is omitted for simplicity.

Bicarbonate (HCO−
3) is alkaline, and a vital component of the pH buffering system^[3] of the human body (maintaining acid-base homeostasis). 70–75% of CO₂ in the body is converted into carbonic acid (H₂CO₃), which can quickly turn into bicarbonate.

With carbonic acid as the central intermediate species, bicarbonate – in conjunction with water, hydrogen ions, and carbon dioxide – forms this buffering system, which is maintained at the volatile equilibrium^[3] required to provide prompt resistance to 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 pancreas in response to the hormone secretin to neutralize the acidic chyme entering the duodenum from the stomach.^[6]

Bicarbonate in the environment

In freshwater ecology, strong photosynthetic activity by freshwater plants in daylight releases gaseous oxygen into the water and at the same time produces bicarbonate ions. These shift the pH upward until in certain circumstances the degree of alkalinity can become toxic to some organisms or can make other chemical constituents such as ammonia toxic. In darkness, when no photosynthesis occurs, respiration processes release carbon dioxide, and no new bicarbonate ions are produced, resulting in a rapid fall in pH.

Other uses

The most common salt of the bicarbonate ion is sodium bicarbonate, NaHCO₃, which is commonly known as baking soda. When heated or exposed to an acid such as acetic acid (vinegar), sodium bicarbonate releases carbon dioxide. This is used as a leavening agent in baking.

The flow of bicarbonate ions from rocks weathered by the carbonic acid in rainwater is an important part of the carbon cycle.

Bicarbonate also serves much 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 bicarbonate is used in digestive biscuit manufacture.

Diagnostics

In diagnostic medicine, the blood value of bicarbonate is one of several indicators of the state of acid–base physiology in the body. It is measured, along with carbon dioxide, chloride, potassium, and sodium, to assess electrolyte levels in an electrolyte panel test (which has Current Procedural Terminology, CPT, code 80051).

The parameter standard bicarbonate concentration (SBC_e) is the bicarbonate concentration in the blood at a P_aCO₂ of 40 mmHg (5.33 kPa), full oxygen saturation and 36 °C.^[7]

Reference ranges for blood tests, comparing blood content of bicarbonate (shown in blue at right) with other constituents.

Bicarbonate compounds

References

1 2 "hydrogencarbonate (CHEBI:17544)". Chemical Entities of Biological Interest (ChEBI). UK: European Institute of Bioinformatics. IUPAC Names.
↑ Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 (PDF), IUPAC, p. 137
1 2 3 "Clinical correlates of pH levels: bicarbonate as a buffer". Biology.arizona.edu. October 2006.
↑ William Hyde Wollaston (1814) "A synoptic scale of chemical equivalents," Philosophical Transactions of the Royal Society, 104: 1-22. On page 11, Wollaston coins the term "bicarbonate": "The next question that occurs relates to the composition of this crystallized carbonate of potash, which I am induced to call bi-carbonate of potash, for the purpose of marking more decidedly the distinction between this salt and that which is commonly called a subcarbonate, and in order to refer at once to the double dose of carbonic acid contained in it."
↑ http://www.newton.dep.anl.gov/askasci/chem99/chem99492.htm
↑ Berne & Levy, Principles of Physiology
↑ Acid Base Balance (page 3)

External links

Look up bicarbonate in Wiktionary, the free dictionary.

Bicarbonates at the US National Library of Medicine Medical Subject Headings (MeSH)

Oxocarbons

Common oxides	CO 2 CO

Exotic oxides	CO 3 CO 4 CO 5 CO 6 C 2O C 2O 2 C 2O 3 C 2O 4 C 2O 4 C 3O C 3O 2 C 3O 3 C 3O 6 C 4O 2 C 4O 4 C 4O 6 C 5O 2 C 5O 5 C 6O 6 C 6O 6 C 8O 8 C 9O 9 C 10O 8 C 10O 10 C 12O 6 C 12O 9 C 12O 12

Polymers	Graphite oxide C₃O₂ CO CO₂

Compounds derived from oxides	Metal carbonyls Carbonic acid Bicarbonates Carbonates Dicarbonates Tricarbonates

Reference ranges for blood tests (CPT 82000–84999)

Electrolytes	Sodium Potassium Chloride Calcium Renal function Creatinine Urea BUN-to-creatinine ratio Plasma osmolality Serum osmolal gap

Acid-base	Anion gap Arterial blood gas Base excess Bicarbonate CO₂ content

Iron tests	Ferritin Serum iron Transferrin saturation Total iron-binding capacity Transferrin Transferrin receptor

Hormones	ACTH stimulation test Thyroid function tests Thyroid-stimulating hormone

Metabolism	Blood lipids

Cardiovascular	Cardiac marker Troponin test CPK-MB test Lactate dehydrogenase Myoglobin Glycogen phosphorylase isoenzyme BB

Liver function tests	Proteins Human serum albumin Serum total protein ALP transaminases ALT AST AST/ALT ratio Bilirubin Unconjugated Conjugated

Pancreas	Amylase Lipase Pancreatic lipase

Inorganic compounds of carbon and related ions

Compounds	CBr₄ CCl₄ CF CF₄ CI₄ CO CO₂ CO₃ COS CS CS₂ CSe₂ C₃O₂ C₃S₂ SiC

Carbon ions	Carbides [:C≡C:]^2–, [::C::]^4–, [:C=C=C:]^4– Cyanides [:C≡N:]^– Cyanates [:O-C≡N:]^– Thiocyanates [:S-C≡N:]^– Fulminates [:C≡N-O:]^– Thiofulminates [:C≡N-S:]^–

Oxides and related	Oxides Metal carbonyls Carbonic acid Bicarbonates Carbonates

This article is issued from Wikipedia - version of the 12/2/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.