:bicarbonate

The bicarbonate ion (hydrogencarbonate ion) is an anion with the empirical formula {{Chem|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 {{chem|HNO|3}}. The bicarbonate ion carries a negative one formal charge and is an amphiprotic species which has both acidic and basic properties. It is both the conjugate base of carbonic acid {{chem|H|2|CO|3}}; and the conjugate acid of {{chem|CO|3|2−}}, the carbonate ion, as shown by these equilibrium reactions:

:{{chem|CO|3|2−}} + 2 H₂O {{eqm}} {{Chem|HCO|3|-}} + H₂O + OH⁻ {{eqm}} H₂CO₃ + 2 OH⁻

:H₂CO₃ + 2 H₂O {{eqm}} {{Chem|HCO|3|-}} + H₃O⁺ + H₂O {{eqm}} {{chem|CO|3|2−}} + 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.{{cite book|last1=Geor|first1=Raymond J.|last2=Coenen|first2=Manfred|last3=Harris|first3=Pat|title=Equine Applied and Clinical Nutrition: Health, Welfare and Performance|date=31 January 2013|publisher=Elsevier Health Sciences|isbn=978-0-7020-5418-1|page=90|language=en|quote=The most common indicator of water quality is the concentration of total dissolved solids (TDS)}}

File:Riassorbimento bicarbonati e respirazione cellulare.svg 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.]]{{clear left}}

Bicarbonate ({{Chem|HCO|3|-}}) is a vital component of the pH buffering system of the human body (maintaining acid–base homeostasis). 70%–75% of CO₂ in the body is converted into carbonic acid (H₂CO₃), which is the conjugate acid of {{Chem|HCO|3|-}} and can quickly turn into it.{{cn|date=February 2024}}

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 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). Recently it has been also demonstrated that cellular bicarbonate metabolism can be regulated by mTORC1 signaling.{{cite journal|vauthors = Ali E, Liponska A, O'Hara B, Amici D, Torno M, Gao P, Asara J, Yap M-N F, Mendillo M, Ben-Sahra I|title = The mTORC1-SLC4A7 axis stimulates bicarbonate import to enhance de novo nucleotide synthesis|journal = Molecular Cell|volume = 82|issue = 1|pages = 3284–3298.e7|date = June 2022|doi = 10.1016/j.molcel.2022.06.008|pmid = 35772404|pmc = 9444906}}

Additionally, bicarbonate plays a key role in the digestive system. It raises the internal pH of the stomach, after highly acidic digestive juices have finished in their digestion of food. 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.Berne & Levy, Principles of Physiology

Bicarbonate is the dominant form of dissolved inorganic carbon in sea water,{{cite web|title=The chemistry of ocean acidification : OCB-OA|url=http://www.whoi.edu/OCB-OA/page.do?pid=112136|website=www.whoi.edu|publisher=Woods Hole Oceanographic Institution|access-date=17 May 2017|language=en-NZ|date=24 September 2012|url-status=live|archive-url=https://web.archive.org/web/20170519193604/http://www.whoi.edu/OCB-OA/page.do?pid=112136|archive-date=19 May 2017}} and in most fresh waters. As such it is an important sink in the carbon cycle.

Some plants like Chara utilize carbonate and produce calcium carbonate (CaCO₃) as a result of biological metabolism.{{Cite journal|last1=Pełechaty|first1=Mariusz|last2=Pukacz|first2=Andrzej|last3=Apolinarska|first3=Karina|last4=Pełechata|first4=Aleksandra|last5=Siepak|first5=Marcin|date=June 2013|editor-last=Porta|editor-first=Giovanna Della|title=The significance of Chara vegetation in the precipitation of lacustrine calcium carbonate|url=https://onlinelibrary.wiley.com/doi/10.1111/sed.12020|journal=Sedimentology|language=en|volume=60|issue=4|pages=1017–1035|doi=10.1111/sed.12020|bibcode=2013Sedim..60.1017P |s2cid=128758128 }}

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.{{cn|date=July 2024}}

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

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.{{Cite web |title=How Baking Soda Works |url=https://www.seriouseats.com/cookie-science-how-baking-soda-works |access-date=2024-11-23 |website=Serious Eats |language=en}}

Ammonium bicarbonate is used in the manufacturing of some cookies, crackers, and biscuits.{{Cite web |title=Ammonium Bicarbonate – Bicarbonate Applications |url=https://www.ahperformance.com/media-library/ammonium-bicarbonate-bicarbonate-applications/ |access-date=2024-11-23 |website=www.ahperformance.com |language=en-US}}

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 chloride, potassium, and sodium, to assess electrolyte levels in an electrolyte panel test (which has Current Procedural Terminology, CPT, code 80051).{{Cite book |url=https://www.worldcat.org/title/on1467227313 |title=CPT 2025: professional edition |date=2024 |publisher=American Medical Association |isbn=978-1-64016-304-1 |editor-last=American Medical Association |location=Chicago, Illinois |oclc=on1467227313}}

The parameter standard bicarbonate concentration (SBC_e) is the bicarbonate concentration in the blood at a P_aCO₂ of {{convert|40|mmHg|kPa|2|abbr=on}}, full oxygen saturation and 36 °C.[http://www.nda.ox.ac.uk/wfsa/html/u13/u1312_03.htm Acid Base Balance (page 3)] {{webarchive|url=https://web.archive.org/web/20020613020114/http://www.nda.ox.ac.uk/wfsa/html/u13/u1312_03.htm|date=2002-06-13}}

File:Reference ranges for blood tests - by molarity.png, comparing blood content of bicarbonate (shown in blue at right) with other constituents.]]

• Sodium bicarbonate
• Potassium bicarbonate
• Caesium bicarbonate
• Magnesium bicarbonate
• Calcium bicarbonate
• Ammonium bicarbonate
• Carbonic acid

• Carbon dioxide
• Carbonate
• Carbonic anhydrase
• Hard water
• Arterial blood gas test
• Henderson-Hasselbach equation

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{{Wiktionary}}

• {{MeshName|Bicarbonates}}

{{Oxides of carbon}}

{{Clinical biochemistry blood tests}}

{{carbon compounds}}

Category:Amphoteric compounds

Category:Carbon oxyanions

Bicarbonates