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| Names | |
|---|---|
| Preferred IUPAC name Sodium acetate | |
| Systematic IUPAC name Sodium ethanoate | |
| Other names Hot ice (sodium acetate trihydrate) | |
| Identifiers | |
3D model (JSmol) |
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| 3595639 | |
| ChEBI |
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| ChEMBL |
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| ChemSpider |
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| DrugBank |
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| ECHA InfoCard | 100.004.386 |
| EC Number |
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| E number | E262(preservatives) |
| 20502 | |
| KEGG |
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| RTECS number |
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| UNII |
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| Properties | |
| C2H3NaO2 | |
| Molar mass | 82.034 g·mol−1 |
| Appearance | White deliquescent powder or crystals |
| Odor | Vinegar (acetic acid) odor when heated to decomposition[1] |
| Density | 1.528 g/cm3 (20 °C, anhydrous) 1.45 g/cm3 (20 °C, trihydrate)[2] |
| Melting point | 324 °C (615 °F; 597 K) (anhydrous) 58 °C (136 °F; 331 K) (trihydrate) |
| Boiling point | 881.4 °C (1,618.5 °F; 1,154.5 K) (anhydrous) 122 °C (252 °F; 395 K) (trihydrate) decomposes |
| Anhydrous: 119 g/100 mL (0 °C) 123.3 g/100 mL (20 °C) 125.5 g/100 mL (30 °C) 137.2 g/100 mL (60 °C) 162.9 g/100 mL (100 °C) Trihydrate: 32.9 g/100 mL (-10 °C) 36.2 g/100 mL (0 °C) 46.4 g/100 mL (20 °C) 82 g/100 mL (50 °C)[3] | |
| Solubility | Soluble inalcohol,hydrazine,SO2[4] |
| Solubility inmethanol | 16 g/100 g (15 °C) 16.55 g/100 g (67.7 °C)[4] |
| Solubility inethanol | Trihydrate: 5.3 g/100 mL |
| Solubility inacetone | 0.5 g/kg (15 °C)[4] |
| Acidity (pKa) | 24 (20 °C)[4] 4.75 (when mixed withCH3COOH as a buffer)[5] |
| Basicity (pKb) | 9.25 |
| −37.6·10−6 cm3/mol | |
Refractive index (nD) | 1.464 |
| Structure | |
| Monoclinic | |
| Thermochemistry | |
| 100.83 J/(mol·K) (anhydrous)[6] 229 J/(mol·K) (trihydrate)[7] | |
Std molar entropy(S⦵298) | 138.1 J/(mol·K) (anhydrous)[6] 262 J/(mol·K) (trihydrate)[2] |
Std enthalpy of formation(ΔfH⦵298) | −709.32 kJ/mol (anhydrous)[4] −1604 kJ/mol (trihydrate)[2] |
Gibbs free energy(ΔfG⦵) | −607.7 kJ/mol (anhydrous)[4] |
| Pharmacology | |
| B05XA08 (WHO) | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Irritant |
| NFPA 704 (fire diamond) | |
| Flash point | >250 °C (482 °F; 523 K)[5] |
| 607 °C (1,125 °F; 880 K)[5] | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 3530 mg/kg (oral, rat) >10000 mg/kg (rabbit, dermal) |
LC50 (median concentration) | >30 g/m3 (rat, 1 h) |
| Safety data sheet (SDS) | Fisher Scientific |
| Related compounds | |
Otheranions | Sodium formate Sodium propionate |
Othercations | Potassium acetate Calcium acetate |
Related compounds | Sodium diacetate |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Sodium acetate, CH3COONa, also abbreviatedNaOAc,[8] is thesodiumsalt ofacetic acid. This salt is colorless,deliquescent, andhygroscopic.
Sodium acetate is used as the carbon source for culturingbacteria. Sodium acetate can also be useful for increasing yields ofDNA isolation by ethanol precipitation.
Sodium acetate is used in thetextile industry to neutralizesulfuric acid waste streams and also as aphotoresist while usinganiline dyes. It is also apickling agent in chrometanning and helps to impedevulcanization ofchloroprene insynthetic rubber production. It is also used to reducestatic electricity during production of disposable cotton pads.
Sodium acetate is used as asealant to mitigate water damage toconcrete. It is environmentally benign and cheaper than the commonly usedepoxy alternative for sealing concrete against waterpermeation.[9]
Sodium acetate (anhydrous) is widely used as ashelf-life extending agent andpH control agent.[10] It is safe to eat at low concentration.[11]
A solution of sodium acetate (a basic salt of acetic acid) and acetic acid can act as abuffer to keep a relatively constant pH level. This is useful especially in biochemical applications where reactions are pH-dependent in a mildly acidic range (pH 4–6).
Sodium acetate is also used inheating pads,hand warmers, and "hot ice". Asupersaturated solution of sodium acetate in water is supplied with a device to initiate crystallization, a process that releases substantial heat.
Sodium acetate trihydrate crystals melt at 58–58.4 °C (136.4–137.1 °F),[12][13] and the liquid sodium acetate dissolves in the releasedwater of crystallization. When heated past the melting point and subsequently allowed to cool, the aqueous solution becomessupersaturated. This solution is capable of cooling to room temperature without forming crystals. By pressing on a metal disc within the heating pad, anucleation center is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The process of crystallization isexothermic.[14] Thelatent heat of fusion is about 264–289 kJ/kg.[12] Unlike some types of heat packs, such as those dependent upon irreversible chemical reactions, a sodium acetate heat pack can be easily reused by immersing the pack in boiling water for a few minutes, until the crystals are completely dissolved, and allowing the pack to slowly cool to room temperature.[15]
Sodium acetate trihydrate can also be used as aphase-change material to store heat, especially to provide domestic hot water for heat pump applications. The heat store consists of a well-insulated container filled with the salt through which pass a pair of copper coils. One coil is used to melt the material by passing hot water from either solar thermal panels or aheat pump. Cold mains water passes through the other coil where its temperature is raised to 40 or 50 ˚C to provide water for washing or cleaning. This process can be cycled almost indefinitely.
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For laboratory use, sodium acetate is inexpensive and usually purchased instead of being synthesized. It is sometimes produced in a laboratory experiment by the reaction ofacetic acid, commonly in the 5–18% solution known asvinegar, withsodium carbonate ("washing soda"),sodium bicarbonate ("baking soda"), orsodium hydroxide ("lye", or "caustic soda"). Any of these reactions produce sodium acetate and water or sodium acetate and carbonic acid. When a sodium and carbonate ion-containing compound is used as the reactant, the carbonate anion (from sodium bicarbonate or carbonate) reacts with the hydrogen from the carboxyl group (-COOH) in acetic acid, formingcarbonic acid. Carbonic acid readily decomposes under normal conditions into gaseous carbon dioxide and water. This is the reaction taking place in the well-known "volcano" that occurs when the household products, baking soda and vinegar, are combined.
Industrially, sodium acetate trihydrate is prepared by reactingacetic acid withsodium hydroxide usingwater as thesolvent.
To manufacture anhydrous sodium acetate industrially, the Niacet Process is used. Sodium metal ingots are extruded through a die to form a ribbon ofsodium metal, usually under an inert gas atmosphere such as N2, and then immersed in anhydrousacetic acid.
Thehydrogen gas is normally a valuable byproduct.
Thecrystal structure ofanhydrous sodium acetate has been described as alternating sodium-carboxylate andmethyl group layers.[17] Sodium acetatetrihydrate's structure consists of distorted octahedral coordination at sodium. Adjacent octahedra share edges to form one-dimensional chains.Hydrogen bonding in two dimensions between acetate ions andwater of hydration links the chains into a three-dimensional network.[18][19]
| Degree of hydration | Anhydrous[17] | Trihydrate[18][19] |
|---|---|---|
| Na coordination |  |  |
| Strongly bonded aggregation |  2D sheet |  1D chain |
| Weakly bonded aggregation |  sheets stacked with hydrophobic surfaces in contact |  chains linked by hydrogen bonds (one chain highlighted in light blue) |
Sodium acetate can be used to form anester with an alkyl halide such asbromoethane:
Sodium acetate undergoes decarboxylation to form methane (CH4) under forcing conditions (pyrolysis in the presence of sodium hydroxide):
Calcium oxide is the typical catalyst used for this reaction.Caesium salts also catalyze this reaction.[citation needed]
