In
inorganic chemistryInorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry...
,
bicarbonate (IUPAC-recommended nomenclature:
hydrogen carbonate) is an intermediate form in the
deprotonationDeprotonation is the removal of a proton from a molecule, forming the conjugate base.The relative ability of a molecule to give up a proton is measured by its pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base...
of
carbonic acidCarbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
. It is an anion with the chemical formula
HHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
CCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
OOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
3−.
Bicarbonate serves a crucial biochemical role in the physiological
pHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
buffering system.
Chemical properties
The
bicarbonate ion (hydrogen carbonate ion) is an anion with the
empirical formulaIn chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic...
HHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
CCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
OOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
3− and a molecular mass of 61.01
daltonsThe unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
; it consists of one central carbon
atomThe atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
surrounded by three oxygen atoms in a
trigonal planarIn chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of a triangle, called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands are identical and all bond angles are 120°. Such species belong to...
arrangement, with a hydrogen atom attached to one of the oxygens. It is isoelectronic with
nitric acidNitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
. The bicarbonate ion carries a negative one
formal chargeIn chemistry, a formal charge is the charge assigned to an atom in a molecule, assuming that electrons in a chemical bond are shared equally between atoms, regardless of relative electronegativity....
and is the
conjugate baseWithin the Brønsted–Lowry acid-base theory , a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases, or donates, a proton in the forward chemical...
of
carbonic acidCarbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
; it is the
conjugate acidWithin the Brønsted–Lowry acid-base theory , a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases, or donates, a proton in the forward chemical...
of , the
carbonateIn chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
ion as shown by these
equilibriumIn a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
reactions.
CO
32− +2 H
2O
HCO3− + H
2O + OH
− H
2CO
3 +2 OH
−
H
2CO
3 +2 H
2O
HCO3− + H
3O
+ + H
2O CO
32− +2 H
3O
+
A bicarbonate salt forms when a positively charged ion attaches to the negatively charged oxygen atoms of the ion, forming an
ionic compoundIn chemistry, an ionic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. Usually, the positively charged portion consists of metal cations and the negatively charged portion is an anion or polyatomic ion. Ions in ionic compounds are held together...
. Many bicarbonates are
solubleSolubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
in
waterAn aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending aq to the relevant formula, such as NaCl. The word aqueous means pertaining to, related to, similar to, or dissolved in water...
at standard temperature and pressure, in particular
sodium bicarbonateSodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. 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...
contributes to
total dissolved solidsTotal Dissolved Solids is a measure of the combined content of all inorganic and organic substances contained in a liquid in: molecular, ionized or micro-granular suspended form. Generally the operational definition is that the solids must be small enough to survive filtration through a sieve...
, a common parameter for assessing
water qualityWater quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...
.
Biochemical role
Bicarbonate is alkaline, and a vital component of the
pHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
buffering system of the human body (maintaining
acid-base homeostasisAcid–base homeostasis is the part of human homeostasis concerning the proper balance between acids and bases, in other words, the pH. The body is very sensitive to its pH level, so strong mechanisms exist to maintain it...
). 70 to 75 percent of CO
2 in the body is converted into
carbonic acidCarbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
(H
2CO
3), which can quickly turn into bicarbonate (HCO
3−).
With carbonic acid as the
central intermediateA reaction intermediate or an intermediate is a molecular entity that is formed from the reactants and reacts further to give the directly observed products of a chemical reaction. Most chemical reactions are stepwise, that is they take more than one elementary step to complete...
speciesChemical species are atoms, molecules, molecular fragments, ions, etc., being subjected to a chemical process or to a measurement. Generally, a chemical species can be defined as an ensemble of chemically identical molecular entities that can explore the same set of molecular energy levels on a...
, bicarbonate – in conjunction with water,
hydrogen ionsIn chemistry, a hydronium ion is the cation , a type of oxonium ion produced by protonation of water. This cation is often used to represent the nature of the proton in aqueous solution, where the proton is highly solvated...
, and
carbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
– forms this buffering system, which is maintained at the volatile equilibrium required to provide prompt resistance to drastic pH changes in both the acidic and
basicFor the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
directions. This is especially important for protecting
tissuesTissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
of the
central nervous systemThe central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
, where pH changes too far outside of the normal range in either direction could prove disastrous. (See
acidosisAcidosis is an increased acidity in the blood and other body tissue . If not further qualified, it usually refers to acidity of the blood plasma....
, or
alkalosisAlkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma . Generally, alkalosis is said to occur when pH of the blood exceeds 7.45. The opposite condition is acidosis .-Causes:...
.)
Bicarbonate also acts to regulate pH in the small intestine. It is released from the
pancreasThe pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
in response to the hormone
secretinSecretin is a hormone that controls the secretions into the duodenum, and also separately, water homeostasis throughout the body. It is produced in the S cells of the duodenum in the crypts of Lieberkühn...
to neutralize the acidic
chymeChyme is the semifluid mass of partly digested food expelled by the stomach into the duodenum.Also known as chymus, it is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum...
entering the duodenum from the stomach
Bicarbonate in the environment
In freshwater ecology, strong
photosyntheticPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
activity by freshwater plants in daylight releases gaseous
oxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
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 bicarbonateSodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. 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...
, NaHCO
3, which is used as
baking powderBaking powder is a dry chemical leavening agent used to increase the volume and lighten the texture of baked goods such as muffins, cakes, scones and American-style biscuits. Baking powder works by releasing carbon dioxide gas into a batter or dough through an acid-base reaction, causing bubbles in...
. When exposed to an
acidAn acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
such as
acetic acidAcetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
(
vinegarVinegar is a liquid substance consisting mainly of acetic acid and water, the acetic acid being produced through the fermentation of ethanol by acetic acid bacteria. Commercial vinegar is produced either by fast or slow fermentation processes. Slow methods generally are used with traditional...
), sodium bicarbonate releases
carbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. This is used as a
leavening agentA leavening agent is any one of a number of substances used in doughs and batters that cause a foaming action which lightens and softens the finished product...
in
bakingBaking is the technique of prolonged cooking of food by dry heat acting by convection, and not by radiation, normally in an oven, but also in hot ashes, or on hot stones. It is primarily used for the preparation of bread, cakes, pastries and pies, tarts, quiches, cookies and crackers. Such items...
.
The flow of bicarbonate ions from rocks weathered by the carbonic acid in rainwater is an important part of the
carbon cycleThe carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
.
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 bicarbonateAmmonium bicarbonate, a compound with formulaNH4, also called bicarbonate of ammonia, ammonium hydrogen carbonate, hartshorn, AmBic or powdered baking ammonia, is the bicarbonate salt of ammonia....
is used in
digestive biscuitA digestive biscuit, sometimes referred to as a sweet-meal biscuit, is a semi-sweet biscuit originated in the United Kingdom and popular worldwide. The term 'digestive' is derived from the belief that they had antacid properties due to the use of sodium bicarbonate when they were first developed...
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.
The parameter
standard bicarbonate concentration (SBC
e) is the bicarbonate concentration in the blood at a
CO2Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
of 40 mmHg (5.33 kPa), full oxygen saturation and 37 degrees Celsius.
Bicarbonate compounds
- Sodium bicarbonate
Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. 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...
- Potassium bicarbonate
Potassium bicarbonate , is a colorless, odorless, slightly basic, salty substance...
- Calcium bicarbonate
Calcium bicarbonate , also called calcium hydrogencarbonate, does not refer to a known solid compound; it exists only in aqueous solution containing the calcium , bicarbonate , and carbonate ions, together with dissolved carbon dioxide...
- Ammonium bicarbonate
Ammonium bicarbonate, a compound with formulaNH4, also called bicarbonate of ammonia, ammonium hydrogen carbonate, hartshorn, AmBic or powdered baking ammonia, is the bicarbonate salt of ammonia....
- Carbonic acid
Carbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
See also
- Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
- Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
- Carbonic anhydrase
The carbonic anhydrases form a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons , a reversible reaction that occurs rather slowly in the absence of a catalyst...
- Hard water
Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...
- Arterial blood gas
An arterial blood gas is a blood test that is performed using blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or...