Bicarbonate
From Wikipedia, the free encyclopedia
For baking soda, see sodium bicarbonate.
"Hydrogen carbonate" redirects here. For the oxoacid, see carbonic acid.
Bicarbonate
Systematic name[hide]
Hydroxidodioxidocarbonate(1-)[1]
Other names[hide]
Hydrogencarbonate[1]
Identifiers
CAS number
71-52-3
PubChem
769
ChemSpider
749
KEGG
C00288
ChEBI
CHEBI:17544
ChEMBL
CHEMBL363707
Beilstein Reference
3903504
Gmelin Reference
49249
3DMet
B00080
Jmol-3D images
Image 1
Image 2
SMILES
[show]
InChI
[show]
Properties
CHO−
Molecular formula
3
Molar mass
61.0168 g mol-1
log P
-0.82
Acidity (pKa)
10.3
Basicity (pKb)
3.7
Except where noted otherwise, data are given for materials in their standard
state (at 25 °C, 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 an anion with the chemical formula HCO3−.
Bicarbonate serves a crucial biochemical role in the physiological pH buffering system.[3]
Contents
[hide]

1 Chemical properties

2 Biochemical role

3 Bicarbonate in the environment

4 Other uses

5 Diagnostics

6 Bicarbonate compounds

7 See also

8 References

9 External links
Chemical properties [edit]
The bicarbonate ion (hydrogen carbonate ion) is an anion with the empirical formula HCO3− and a molecular
mass of 61.01 daltons; it consists of one central carbon atom surrounded by three oxygen atoms in a trigonal
planararrangement, with a hydrogen atom attached to one of the oxygens. It is isoelectronic with nitric
acid HNO3. The bicarbonate ion carries a negative one formal charge and is the conjugate base of carbonic
acid H2CO3; it is theconjugate acid of CO2−
3, the carbonate ion, as shown by these equilibrium reactions.
CO32− + 2 H2O
H2CO3 + 2 H2O
HCO3− + H2O + OH−
HCO3− + H3O+ + H2O
H2CO3 +2 OH−
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 water at standard
temperature and pressure, in particular sodium bicarbonate contributes to total dissolved solids, a
common parameter for assessing water quality.[citation needed]
Biochemical role [edit]
Bicarbonate 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 (HCO3−).
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 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 pancreas in
response to the hormone secretin to neutralize the acidic chymeentering the duodenum from the
stomach.[4]
Bicarbonate in the environment [edit]
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 [edit]
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 acidsuch 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 [edit]
In diagnostic medicine, the blood value of bicarbonate is one of several indicators of the state of acidbase physiology in the body.
The parameter standard bicarbonate concentration (SBCe) is the bicarbonate concentration in the
blood at a PaCO2 of 40 mmHg (5.33 kPa), full oxygen saturation and 36 °C.[5]
Reference ranges for blood tests, comparing blood content of bicarbonate (shown in blue at right) with other
constituents.
Bicarbonate compounds [edit]

Sodium bicarbonate

Potassium bicarbonate

Calcium bicarbonate

Ammonium bicarbonate

Carbonic acid
See also [edit]

Carbon dioxide

Carbonate

Carbonic anhydrase

Hard water

Arterial blood gas