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Names | |||
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IUPAC name sodium hydrogencarbonate | |||
Other names Baking soda, bicarb (laboratory slang), bicarbonate of soda, nahcolite, natrium hydrogen carbonate, natron | |||
Identifiers | |||
3D model (JSmol) | |||
4153970 | |||
ChEBI | |||
ChEMBL | |||
ChemSpider | |||
DrugBank | |||
ECHA InfoCard | 100.005.122 | ||
EC Number |
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E number | E500(ii) (acidity regulators, ...) | ||
KEGG | |||
MeSH | Sodium+bicarbonate | ||
PubChem CID | |||
RTECS number |
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UNII | |||
CompTox Dashboard (EPA) | |||
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Properties | |||
NaHCO 3 | |||
Molar mass | 84.0066 g mol−1 | ||
Appearance | White crystals | ||
Odor | Odorless | ||
Density |
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Melting point | (Decomposes to sodium carbonate starting at 50 °C [1] [2] ) | ||
Solubility | 0.02 wt% acetone, 2.13 wt% methanol @22 °C. [5] insoluble in ethanol | ||
log P | −0.82 | ||
Acidity (pKa) | |||
Refractive index (nD) | nα = 1.377 nβ = 1.501 nγ = 1.583 | ||
Structure | |||
Monoclinic | |||
Thermochemistry | |||
Heat capacity (C) | 87.6 J/mol K [7] | ||
Std molar entropy (S⦵298) | 101.7 J/mol K [7] | ||
Std enthalpy of formation (ΔfH⦵298) | −950.8 kJ/mol [7] | ||
Gibbs free energy (ΔfG⦵) | −851.0 kJ/mol [7] | ||
Pharmacology | |||
B05CB04 ( WHO ) B05XA02 ( WHO ), QG04BQ01 ( WHO ) | |||
Intravenous, oral | |||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards | Causes serious eye irritation | ||
NFPA 704 (fire diamond) | |||
Flash point | Incombustible | ||
Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) | 4220 mg/kg (rat, oral) [8] | ||
Safety data sheet (SDS) | External MSDS | ||
Related compounds | |||
Other anions | Sodium carbonate | ||
Other cations | |||
Related compounds | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate [9] ), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation (Na+) and a bicarbonate anion (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 (sodium carbonate). The natural mineral form is nahcolite, although it is more commonly found as a component of the mineral trona. [10]
As it has long been known and widely used, the salt has many different names such as baking soda, bread soda, cooking soda, brewing soda and bicarbonate of soda and can often be found near baking powder in stores. The term baking soda is more common in the United States, while bicarbonate of soda is more common in Australia, the United Kingdom, and New Zealand. [11] Abbreviated colloquial forms such as sodium bicarb, bicarb soda, bicarbonate, and bicarb are common. [12]
The prefix bi- in "bicarbonate" comes from an outdated naming system predating molecular knowledge. It is based on the observation that there is twice as much carbonate (CO3−2) per sodium in sodium bicarbonate (NaHCO3) as there is in sodium carbonate (Na2CO3). [13] The modern chemical formulas of these compounds now express their precise chemical compositions which were unknown when the name bi-carbonate of potash was coined (see also: bicarbonate).
In cooking, baking soda is primarily used in baking as a leavening agent. When it reacts with acid or is heated, carbon dioxide is released, which causes expansion of the batter and forms the characteristic texture and grain in cakes, quick breads, soda bread, and other baked and fried foods. When an acid is used, the acid–base reaction can be generically represented as follows: [14]
Acidic materials that induce this reaction include hydrogen phosphates, cream of tartar, lemon juice, yogurt, buttermilk, cocoa, and vinegar. Baking soda may be used together with sourdough, which is acidic, making a lighter product with a less acidic taste. [15] Since the reaction occurs slowly at room temperature, mixtures (cake batter, etc.) can be allowed to stand without rising until they are heated in the oven.[ citation needed ]
Heat can also by itself cause sodium bicarbonate to act as a raising agent in baking because of thermal decomposition, releasing carbon dioxide at temperatures above 80 °C (180 °F), as follows: [16]
When used this way on its own, without the presence of an acidic component (whether in the batter or by the use of a baking powder containing acid), only half the available CO2 is released (one CO2 molecule is formed for every two equivalents of NaHCO3). Additionally, in the absence of acid, thermal decomposition of sodium bicarbonate also produces sodium carbonate, which is strongly alkaline and gives the baked product a bitter, soapy taste and a yellow color.
Baking powder, also sold for cooking, contains around 30% of bicarbonate, and various acidic ingredients that are activated by the addition of water, without the need for additional acids in the cooking medium. [17] [18] [19] Many forms of baking powder contain sodium bicarbonate combined with calcium acid phosphate, sodium aluminium phosphate, or cream of tartar. [20] Baking soda is alkaline; the acid used in baking powder avoids a metallic taste when the chemical change during baking creates sodium carbonate. [21]
It is often used in conjunction with other bottled water food additives to add taste. [22] Its European Union E number is E500. [23]
Sodium bicarbonate is one of the main components of the common "black snake" firework. The effect is caused by the thermal decomposition, which produces carbon dioxide gas to produce a long snake-like ash as a combustion product of the other main component, sucrose. [24] Sodium bicarbonate also delays combustion reactions through the release of carbon dioxide and water, both of which are flame retardants, when heated.
It has weak disinfectant properties [25] [26] and it may be an effective fungicide against some organisms. [27] As baking soda will absorb musty smells, it has become a reliable method for used booksellers when making books less malodorous. [28]
Sodium bicarbonate can be used to extinguish small grease or electrical fires by being thrown over the fire, as heating of sodium bicarbonate releases carbon dioxide. [29] However, it should not be applied to fires in deep fryers; the sudden release of gas may cause the grease to splatter. [29] Sodium bicarbonate is used in BC dry chemical fire extinguishers as an alternative to the more corrosive monoammonium phosphate in ABC extinguishers. The alkaline nature of sodium bicarbonate makes it the only dry chemical agent, besides Purple-K, that was used in large-scale fire suppression systems installed in commercial kitchens. [30]
Sodium bicarbonate has several fire-extinguishing mechanisms that act simultaneously. It decomposes into water and carbon dioxide when heated, an endothermic reaction that deprives the fire of heat. In addition, it forms intermediates that can scavenge the free radicals which are responsible for the propagation of fire. [31] With grease fires specifically, it also has a mild saponification effect, producing a soapy foam that can help smother the fire. [30]
Sodium bicarbonate reacts spontaneously with acids, releasing CO2 gas as a reaction product. It is commonly used to neutralize unwanted acid solutions or acid spills in chemical laboratories. [32] It is not appropriate to use sodium bicarbonate to neutralize base [33] even though it is amphoteric, reacting with both acids and bases. [34]
Sodium bicarbonate is taken as a sports supplement to improve muscular endurance. [35] Studies conducted mostly in males have shown that sodium bicarbonate is most effective in enhancing performance in short-term, high-intensity activities. [36]
Sodium bicarbonate can prevent the growth of fungi when applied on leaves, although it will not kill the fungus. Excessive amounts of sodium bicarbonate can cause discolouration of fruits (two percent solution) and chlorosis (one percent solution). [37] Sodium bicarbonate is also commonly used as a free choice dietary supplement in sheep to help prevent bloat.
Sodium bicarbonate mixed with water can be used as an antacid to treat acid indigestion and heartburn. [38] [39] Its reaction with stomach acid produces salt, water, and carbon dioxide:
A mixture of sodium bicarbonate and polyethylene glycol such as PegLyte, [40] dissolved in water and taken orally, is an effective gastrointestinal lavage preparation and laxative prior to gastrointestinal surgery, gastroscopy, etc.[ citation needed ]
Intravenous sodium bicarbonate in an aqueous solution is sometimes used for cases of acidosis, or when insufficient sodium or bicarbonate ions are in the blood. [41] In cases of respiratory acidosis, the infused bicarbonate ion drives the carbonic acid/bicarbonate buffer of plasma to the left, and thus raises the pH. For this reason, sodium bicarbonate is used in medically supervised cardiopulmonary resuscitation. Infusion of bicarbonate is indicated only when the blood pH is markedly low (< 7.1–7.0). [42]
HCO3− is used for treatment of hyperkalemia, as it will drive K+ back into cells during periods of acidosis. [43] Since sodium bicarbonate can cause alkalosis, it is sometimes used to treat aspirin overdoses. Aspirin requires an acidic environment for proper absorption, and a basic environment will diminish aspirin absorption in cases of overdose. [44] Sodium bicarbonate has also been used in the treatment of tricyclic antidepressant overdose. [45] It can also be applied topically as a paste, with three parts baking soda to one part water, to relieve some kinds of insect bites and stings (as well as accompanying swelling). [46]
Some alternative practitioners, such as Tullio Simoncini, have promoted baking soda as a cancer cure, which the American Cancer Society has warned against due to both its unproven effectiveness and potential danger in use. [47] Edzard Ernst has called the promotion of sodium bicarbonate as a cancer cure "one of the more sickening alternative cancer scams I have seen for a long time". [48]
Sodium bicarbonate can be added to local anaesthetics, to speed up the onset of their effects and make their injection less painful. [49] It is also a component of Moffett's solution, used in nasal surgery. [50]
It has been proposed that acidic diets weaken bones. [51] One systematic meta-analysis of the research shows no such effect. [52] Another also finds that there is no evidence that alkaline diets improve bone health, but suggests that there "may be some value" to alkaline diets for other reasons. [53]
Antacid (such as baking soda) solutions have been prepared and used by protesters to alleviate the effects of exposure to tear gas during protests.[ failed verification ] [54]
Similarly to its use in baking, sodium bicarbonate is used together with a mild acid such as tartaric acid as the excipient in effervescent tablets: when such a tablet is dropped in a glass of water, the carbonate leaves the reaction medium as carbon dioxide gas (HCO3− + H+ → H2O + CO2↑ or, more precisely, HCO3− + H3O+ → 2 H2O + CO2↑). This makes the tablet disintegrate, leaving the medication suspended and/or dissolved in the water together with the resulting salt (in this example, sodium tartrate). [55]
Sodium bicarbonate is also used as an ingredient in some mouthwashes. It has anticaries and abrasive properties. [56] It works as a mechanical cleanser on the teeth and gums, neutralizes the production of acid in the mouth, and also acts as an antiseptic to help prevent infections. [57] [58] Sodium bicarbonate in combination with other ingredients can be used to make a dry or wet deodorant. [59] [60] Sodium bicarbonate may be used as a buffering agent, combined with table salt, when creating a solution for nasal irrigation. [61]
It is used in eye hygiene to treat blepharitis. This is done by adding a teaspoon of sodium bicarbonate to cool water that was recently boiled followed by gentle scrubbing of the eyelash base with a cotton swab dipped in the solution. [62] [63]
Sodium bicarbonate is used as a cattle feed supplement, in particular as a buffering agent for the rumen. [64]
Sodium bicarbonate is used in a process to remove paint and corrosion called sodablasting. As a blasting medium, sodium bicarbonate is used to remove surface contamination from softer and less resilient substrates such as aluminium, copper, or timber that could be damaged by silica sand abrasive media. [65]
A manufacturer recommends a paste made from baking soda with minimal water as a gentle scouring powder. [29] Such a paste can be useful in removing surface rust because the rust forms a water-soluble compound when in a concentrated alkaline solution. [66] Cold water should be used since hot-water solutions can corrode steel. [67] Sodium bicarbonate attacks the thin protective oxide layer that forms on aluminium, making it unsuitable for cleaning this metal. [68] A solution in warm water will remove the tarnish from silver when the silver is in contact with a piece of aluminium foil. [68] [69] Baking soda is commonly added to washing machines as a replacement for water softener and to remove odors from clothes. When diluted with warm water, it is also almost as effective in removing heavy tea and coffee stains from cups as sodium hydroxide.
During the Manhattan Project to develop the nuclear bomb in the early 1940s, the chemical toxicity of uranium was an issue. Uranium oxides were found to stick very well to cotton cloth and did not wash out with soap or laundry detergent. However, the uranium would wash out with a 2% solution of sodium bicarbonate. Clothing can become contaminated with toxic dust of depleted uranium (DU), which is very dense, hence it is used for counterweights in a civilian context and in armour-piercing projectiles. DU is not removed by normal laundering; washing with about 6 ounces (170 g) of baking soda in 2 gallons (7.5 L) of water will help wash it out. [70]
It is often claimed that baking soda is an effective odor remover [71] [ better source needed ] and recommended that an open box be kept in the refrigerator to absorb odor. [72] This idea was promoted by the leading U.S. brand of baking soda, Arm & Hammer, in an advertising campaign starting in 1972. [73] Though this campaign is considered a classic of marketing, leading within a year to more than half of American refrigerators containing a box of baking soda, [74] [75] there is little evidence that it is effective in this application. [76] [77]
An educational science experiment known as the "Baking Soda and Vinegar Volcano" uses the acid-base reaction with vinegar acid to mimic a volcanic eruption. The rapid production of CO2 causes the liquid to foam up and overflow its container. Other ingredients such as dish soap and food coloring can be added to enhance the visual effect. [78] If this reaction is performed inside of a closed vessel (such as a bottle) with no way for gas to escape, it can cause an explosion if the pressure is high enough.
Sodium bicarbonate is an amphoteric compound. [34] Aqueous solutions are mildly alkaline due to the formation of carbonic acid and hydroxide ion: [34]
Sodium bicarbonate can sometimes be used as a mild neutralization agent and a safer alternative to strong bases like sodium hydroxide. [79] Reaction of sodium bicarbonate and an acid produces a salt and carbonic acid, which readily decomposes to carbon dioxide and water: [79]
Sodium bicarbonate reacts with acetic acid (found in vinegar), producing sodium acetate, water, and carbon dioxide:
Sodium bicarbonate reacts with bases such as sodium hydroxide to form carbonates:
At temperatures from 80–100 °C (176–212 °F), sodium bicarbonate gradually decomposes into sodium carbonate, water, and carbon dioxide. The conversion is faster at 200 °C (392 °F): [80]
Most bicarbonates undergo this dehydration reaction. Further heating converts the carbonate into the oxide (above 850 °C/1,560 °F): [80]
The generation of carbon dioxide and water partially explain the fire-extinguishing properties of NaHCO3, [30] although other factors like heat absorption and radical scavenging are more significant. [31]
In nature, sodium bicarbonate occurs almost exclusively as either nahcolite or trona. Trona is more common, as nahcolite is more soluble in water and the chemical equilibrium between the two minerals favors trona. [10] Significant nahcolite deposits are in the United States, Botswana and Kenya, Uganda, Turkey, and Mexico. [81] The biggest trona deposits are in the Green River basin in Wyoming. [82]
Nahcolite is sometimes found as a component of oil shale. [83]
If kept cool (room temperature) and dry (an airtight container is recommended to keep out moist air), sodium bicarbonate can be kept without a significant amount of decomposition for at least two or three years. [84] [85] [86] [87]
The word natron has been in use in many languages throughout modern times (in the forms of anatron, natrum and natron) and originated (like Spanish, French and English natron as well as 'sodium') via Arabic naṭrūn (or anatrūn; cf. the Lower Egyptian “Natrontal” Wadi El Natrun, where a mixture of sodium carbonate and sodium hydrogen carbonate for the dehydration of mummies was used [88] ) from Greek nítron (νίτρον) (Herodotus; Attic lítron (λίτρον)), which can be traced back to ancient Egyptian ntr. The Greek nítron (soda, saltpeter) was also used in Latin (sal) nitrum and in German Salniter (the source of Nitrogen, Nitrat etc.). [89] [90] The word saleratus, from Latin sal æratus (meaning "aerated salt"), was widely used in the 19th century for both sodium bicarbonate and potassium bicarbonate. [91]
In 1791, French chemist Nicolas Leblanc produced sodium carbonate (also known as soda ash). Pharmacist Valentin Rose the Younger is credited with the discovery of sodium bicarbonate in 1801 in Berlin. In 1846, two American bakers, John Dwight and Austin Church, established the first factory in the United States to produce baking soda from sodium carbonate and carbon dioxide. [92]
Saleratus, potassium or sodium bicarbonate, is mentioned in the novel Captains Courageous by Rudyard Kipling as being used extensively in the 1800s in commercial fishing to prevent freshly caught fish from spoiling. [93]
In 1919, US Senator Lee Overman declared that bicarbonate of soda could cure the Spanish flu. In the midst of the debate on 26 January 1919, he interrupted the discussion to announce the discovery of a cure. "I want to say, for the benefit of those who are making this investigation," he reported, "that I was told by a judge of a superior court in the mountain country of North Carolina they have discovered a remedy for this disease." The purported cure implied a critique of modern science and an appreciation for the simple wisdom of simple people. "They say that common baking soda will cure the disease," he continued, "that they have cured it with it, that they have no deaths up there at all; they use common baking soda, which cures the disease." [94]
Sodium bicarbonate is produced industrially from sodium carbonate: [95]
It is produced on the scale of about 100,000 tonnes/year (as of 2001) [ dubious – discuss ] [96] with a worldwide production capacity of 2.4 million tonnes per year (as of 2002). [97] Commercial quantities of baking soda are also produced by a similar method: soda ash, mined in the form of the ore trona, is dissolved in water and treated with carbon dioxide. Sodium bicarbonate precipitates as a solid from this solution.[ citation needed ]
Regarding the Solvay process, sodium bicarbonate is an intermediate in the reaction of sodium chloride, ammonia, and carbon dioxide. The product however shows low purity (75pc).[ citation needed ]
Although of no practical value, NaHCO3 may be obtained by the reaction of carbon dioxide with an aqueous solution of sodium hydroxide:[ citation needed ]
Naturally occurring deposits of nahcolite (NaHCO3) are found in the Eocene-age (55.8–33.9 Mya) Green River Formation, Piceance Basin in Colorado. Nahcolite was deposited as beds during periods of high evaporation in the basin. It is commercially mined using common underground mining techniques such as bore, drum, and longwall mining in a fashion very similar to coal mining.[ citation needed ]
It is also produced by solution mining, pumping heated water through nahcolite beds and crystallizing the dissolved nahcolite through a cooling crystallization process.
Since nahcolite is sometimes found in shale, it can be produced as a co-product of shale oil extraction, where it is recovered by solution mining. [83]
Sodium bicarbonate, as "bicarbonate of soda", was a frequent source of punch lines for Groucho Marx in Marx Brothers movies. In Duck Soup , Marx plays the leader of a nation at war. In one scene, he receives a message from the battlefield that his general is reporting a gas attack, and Groucho tells his aide: "Tell him to take a teaspoonful of bicarbonate of soda and a half a glass of water." [98] In A Night at the Opera , Groucho's character addresses the opening night crowd at an opera by saying of the lead tenor: "Signor Lassparri comes from a very famous family. His mother was a well-known bass singer. His father was the first man to stuff spaghetti with bicarbonate of soda, thus causing and curing indigestion at the same time." [99]
In the Joseph L. Mankewicz classic All About Eve , the Max Fabian character (Gregory Ratoff) has an extended scene with Margo Channing (Bette Davis) in which, suffering from heartburn, he requests and then drinks bicarbonate of soda, eliciting a prominent burp. Channing promises to always keep a box of bicarb with Max's name on it.
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula HCO−
3.
A carbonate is a salt of carbonic acid,, characterized by the presence of the carbonate ion, a polyatomic ion with the formula CO2−3. The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate groupO=C(−O−)2.
Natron is a naturally occurring mixture of sodium carbonate decahydrate (Na2CO3·10H2O, a kind of soda ash) and around 17% sodium bicarbonate (also called baking soda, NaHCO3) along with small quantities of sodium chloride and sodium sulfate. Natron is white to colourless when pure, varying to gray or yellow with impurities. Natron deposits are sometimes found in saline lake beds which arose in arid environments. Throughout history natron has had many practical applications that continue today in the wide range of modern uses of its constituent mineral components.
Sodium carbonate is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water. Historically, it was extracted from the ashes of plants grown in sodium-rich soils, and because the ashes of these sodium-rich plants were noticeably different from ashes of wood, sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process, as well as by carbonating sodium hydroxide which is made using the chloralkali process.
Baking powder is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid. The base and acid are prevented from reacting prematurely by the inclusion of a buffer such as cornstarch. Baking powder is used to increase the volume and lighten the texture of baked goods. It works by releasing carbon dioxide gas into a batter or dough through an acid–base reaction, causing bubbles in the wet mixture to expand and thus leavening the mixture.
Potassium bicarbonate (IUPAC name: potassium hydrogencarbonate, also known as potassium acid carbonate) is the inorganic compound with the chemical formula KHCO3. It is a white solid.
Magnesium carbonate, MgCO3, is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.
Ammonium bicarbonate is an inorganic compound with formula (NH4)HCO3. The compound has many names, reflecting its long history. Chemically speaking, it is the bicarbonate salt of the ammonium ion. It is a colourless solid that degrades readily to carbon dioxide, water and ammonia.
The Solvay process or ammonia–soda process is the major industrial process for the production of sodium carbonate (soda ash, Na2CO3). The ammonia–soda process was developed into its modern form by the Belgian chemist Ernest Solvay during the 1860s. The ingredients for this are readily available and inexpensive: salt brine (from inland sources or from the sea) and limestone (from quarries). The worldwide production of soda ash in 2005 was estimated at 42 million tonnes, which is more than six kilograms (13 lb) per year for each person on Earth. Solvay-based chemical plants now produce roughly three-quarters of this supply, with the remaining being mined from natural deposits. This method superseded the Leblanc process.
Ammonium carbonate is a chemical compound with the chemical formula [NH4]2CO3. It is an ammonium salt of carbonic acid. It is composed of ammonium cations [NH4]+ and carbonate anions CO2−3. Since ammonium carbonate readily degrades to gaseous ammonia and carbon dioxide upon heating, it is used as a leavening agent and also as smelling salt. It is also known as baker's ammonia and is a predecessor to the more modern leavening agents baking soda and baking powder. It is a component of what was formerly known as sal volatile and salt of hartshorn, and produces a pungent smell when baked. It comes in the form of a white powder or block, with a molar mass of 96.09 g/mol and a density of 1.50 g/cm3. It is a strong electrolyte.
Sodium acetate, CH3COONa, also abbreviated NaOAc, is the sodium salt of acetic acid. This salt is colorless deliquescent, and Hygroscopic.
Calcium bicarbonate, also called calcium hydrogencarbonate, has the chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing calcium (Ca2+), bicarbonate (HCO−
3), and carbonate (CO2−
3) ions, together with dissolved carbon dioxide (CO2). The relative concentrations of these carbon-containing species depend on the pH; bicarbonate predominates within the range 6.36–10.25 in fresh water.
"Black snake" is a term that can refer to at least three similar types of fireworks: the Pharaoh's snake, the sugar snake, or a popular retail composition marketed under various product names but usually known as "black snake". The "Pharaoh's snake" or "Pharaoh's serpent" is the original version of the black snake experiment. It produces a more impressive snake, but its execution depends upon mercury (II) thiocyanate, which is no longer in common use due to its toxicity. For a "sugar snake", sodium bicarbonate and sugar are the commonly used chemicals.
Monosodium citrate, more correctly, sodium dihydrogen citrate (Latin: natrium citricum acidulatum), is an acid salt of citric acid. Disodium citrate and trisodium citrate are also known. It can be prepared by partial neutralisation of citric acid with an aqueous solution of sodium bicarbonate or carbonate. It has a slightly acidic taste.
Disodium pyrophosphate or sodium acid pyrophosphate (SAPP) is an inorganic compound with the chemical formula Na2H2P2O7. It consists of sodium cations (Na+) and dihydrogen pyrophosphate anions (H2P2O2−7). It is a white, water-soluble solid that serves as a buffering and chelating agent, with many applications in the food industry. When crystallized from water, it forms a hexahydrate, but it dehydrates above room temperature. Pyrophosphate is a polyvalent anion with a high affinity for polyvalent cations, e.g. Ca2+.
Alkali, or alkaline, soils are clay soils with high pH, a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which can induce basicity. Sometimes these soils are also referred to as alkaline sodic soils. Alkaline soils are basic, but not all basic soils are alkaline.
Magnesium bicarbonate or magnesium hydrogencarbonate, Mg(HCO3)2, is the bicarbonate salt of magnesium. It can be formed through the reaction of dilute solutions of carbonic acid (such as seltzer water) and magnesium hydroxide (milk of magnesia).
The residual sodium carbonate (RSC) index of irrigation water or soil water is used to indicate the alkalinity hazard for soil. The RSC index is used to find the suitability of the water for irrigation in clay soils which have a high cation exchange capacity. When dissolved sodium in comparison with dissolved calcium and magnesium is high in water, clay soil swells or undergoes dispersion which drastically reduces its infiltration capacity.
The dry ice color show is a demonstration of the chemical formation of carbonic acid by the dissolution of dry ice in water. The dry ice color show is usually performed in classrooms to demonstrate the properties of acids and bases, their effect on pH indicators, and the sublimation of dry ice. Setup is simple and generally involves only minor hazards, the main one being the low temperature of dry ice, which can cause frostbite upon skin contact. The carbonic acid formed in the demonstration is a weak acid and is not hazardous, being present in numerous consumer products including tonic water, soda, and beer.
Total inorganic carbon is the sum of the inorganic carbon species.
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