sodium sesquicarbonate
{{More citations needed|date=May 2017}}
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| ImageFile =Sodium sesquicarbonate.svg
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|Section1={{Chembox Identifiers
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| UNII = Y1X815621J
| InChI = 1S/2CH2O3.3Na/c2*2-1(3)4;;;/h2*(H2,2,3,4);;;/q;;3*+1/p-3
| InChIKey = WCTAGTRAWPDFQO-UHFFFAOYSA-K
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| SMILES = C(=O)(O)[O-].C(=O)([O-])[O-].[Na+].[Na+].[Na+]
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| CASNo = 533-96-0
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| PubChem = 10791
| EINECS = 208-580-9
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|Section2={{Chembox Properties
| Formula = Na3H(CO3)2·2H2O
| Appearance = white, needle-like
| Density = 2.112 g/cm3 (dihydrate)
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| Solubility = dihydrate
13 g/100 mL (0 °C)
42 g/100 mL (100 °C)
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| RefractIndex = 1.5073 (dihydrate)
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|Section3={{Chembox Structure
| CrystalStruct = monoclinic (dihydrate)
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Sodium sesquicarbonate (systematic name: trisodium hydrogendicarbonate) Na3H(CO3)2 is a double salt of sodium bicarbonate and sodium carbonate (NaHCO3 · Na2CO3), and has a needle-like crystal structure. However, the term is also applied to an equimolar mixture of those two salts, with whatever water of hydration the sodium carbonate includes, supplied as a powder.
The dihydrate, Na3H(CO3)2 · 2H2O, occurs in nature as the evaporite mineral trona.{{cite web|url=https://www.mindat.org/min-4031.html|title=Trona}}
Due to concerns about the toxicity of borax which was withdrawn as a cleaning and laundry product, sodium sesquicarbonate is sold in the European Union (EU) as "Borax substitute".{{cite web |url=http://www.dri-pak.co.uk/cleaning-products/borax-substitute/ |title=Borax substitute – laundry booster, multi purpose cleaner, bath soak |website=Dri-Pak |date=27 April 2015 |author= |accessdate=28 May 2017 |archive-date=2 July 2019 |archive-url=https://web.archive.org/web/20190702082328/https://www.dri-pak.co.uk/cleaning-products/borax-substitute/ |url-status=dead }} It is also known as one of the E number food additives E500(iii).
Uses
Sodium sesquicarbonate is used in bath salts, swimming pools, as an alkalinity source for water treatment, and as a phosphate-free product replacing the trisodium phosphate for heavy duty cleaning.[https://savogran.com/pdfs/TSP_PF_MS.pdf Savogran's phosphate-free TSP substitute][https://www.sunnysidecorp.com/product.php?p=c&b=s&n=64116 Sunnyside's phosphate-free TSP substitute]
Sodium sesquicarbonate is used in the conservation of copper and copper alloy artifacts that corrode due to contact with salt (called "bronze disease" due to its effect on bronze). The chloride from salt forms copper(I) chloride. In the presence of oxygen and water, even the small amount of moisture in the atmosphere, the cuprous chloride forms copper(II) chloride and hydrochloric acid, the latter of which dissolves the metal and forms more cuprous chloride in a self-sustaining reaction that leads to the entire destruction of the object. Treatment with sodium sesquicarbonate removes copper(II) chlorides from the corroded layer.{{Citation needed|date=April 2019}}
It is also used as a precipitating water softener, which combines with hard water minerals (calcium- and magnesium-based minerals) to form an insoluble precipitate, removing these hardness minerals from the water.[http://www.cleaning101.com/laundry/fact/fact_sheet4.cfm According to cleaning101.com] {{webarchive|url=https://web.archive.org/web/20071015092610/http://www.cleaning101.com/laundry/fact/fact_sheet4.cfm |date=2007-10-15 }} It is the carbonate moiety which forms the precipitate, the bicarbonate being included to moderate the material's alkalinity.
In Chinese cuisine, it is known as mǎyájiǎn (simplified:马牙碱 traditional: 馬牙鹼) which roughly translates to “horse tooth alkaline” and traditionally used as an ingredient in the marinade for century eggs, a dish generally made from duck eggs preserved whole in an highly alkaline mixture{{cn|reason=doesn't match text in century egg; google only finds a recent thread on reddit|date=September 2024}}.
References
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{{Sodium compounds}}
{{Carbonates}}
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