Sodium acetate

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This article is about sodium acetate. For other uses of hot ice, see Hot ice (disambiguation).
Sodium acetate
Skeletal formula of sodium acetate
Sodium acetate
Identifiers
CAS number 127‑09‑3 N, 6131‑90‑4 (trihydrate)
PubChem 517045
ChemSpider 29105 YesY
UNII NVG71ZZ7P0 YesY
EC number 204-823-8
ChEBI CHEBI:32954 YesY
ChEMBL CHEMBL1354 YesY
RTECS number AJ4300010 (anhydrous)
AJ4580000
ATC code B05XA08
Jmol-3D images Image 1
Properties
Molecular formula C2H3NaO2
Molar mass 82.03 g mol−1
Appearance White deliquescent powder
Odor Vinegar
Density 1.528 g/cm3 (20 °C, anhydrous)
1.45 g/cm3 (20 °C, trihydrate)[1]
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
Solubility in water 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)[2]
Solubility Soluble in alcohol, hydrazine, SO2[3]
Solubility in methanol 16 g/100 g (15 °C)
16.55 g/100 g (67.7 °C)[3]
Solubility in ethanol Trihydrate:
5.3 g/100 mL
Solubility in acetone 0.5 g/kg (15 °C)[3]
Acidity (pKa) 24 (20 °C)[3]
4.76 in CH3COOH[4]
Basicity (pKb) 9.25
Refractive index (nD) 1.464
Structure
Crystal structure Monoclinic
Thermochemistry
Specific
heat capacity
C
100.83 J/mol·K (anhydrous)[5]
229 J/mol·K (trihydrate)[6]
Std molar
entropy
So298
138.1 J/mol·K (anhydrous)[5]
262 J/mol·K (trihydrate)[1]
Std enthalpy of
formation
ΔfHo298
-709.32 kJ/mol (anhydrous)[3]
-1604 kJ/mol (trihydrate)[1]
Gibbs free energy ΔG -607.7 kJ/mol (anhydrous)[3]
Hazards
MSDS External MSDS
Main hazards Irritant
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point >250 °C (482 °F; 523 K) [4]
Autoignition temperature 600 °C (1,112 °F; 873 K) [4]
LD50 3530 mg/kg (oral, rat)
Related compounds
Other anions Sodium formate
Sodium propionate
Other cations Potassium acetate
Calcium acetate
Related compounds Sodium diacetate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Sodium acetate, CH3COONa, also abbreviated NaOAc,[7] also known as sodium ethanoate, is the sodium salt of acetic acid. This colourless salt has a wide range of uses.

Applications[edit]

Industrial[edit]

Sodium acetate is used in the textile industry to neutralize sulfuric acid waste streams and also as a photoresist while using aniline dyes. It is also a pickling agent in chrome tanning and helps to impede vulcanization of chloroprene in synthetic rubber production. In processing cotton for disposable cotton pads, sodium acetate is used to eliminate the buildup of static electricity.

Concrete longevity[edit]

Sodium acetate is used to mitigate water damage to concrete by acting as a concrete sealant, while also being environmentally benign and cheaper than the commonly-used epoxy alternative for sealing concrete against water permeation.[8]

Food[edit]

Sodium acetate may be added to food as a seasoning, sometimes in the form of sodium diacetate, a one-to-one complex of sodium acetate and acetic acid,[9] given the E-number E262. It is often used to give potato chips a salt and vinegar flavor.

Buffer solution[edit]

As the conjugate base of acetic acid, a solution of sodium acetate and acetic acid can act as a buffer 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).

Heating pad[edit]

A hand warmer containing a supersaturated solution of sodium acetate which releases heat upon crystallization

Sodium acetate is also used in heating pads, hand warmers, and hot ice. Sodium acetate trihydrate crystals melt at 137.12 °F/58.4 °C,[10] (to 136.4 °F/58 °C)[11] dissolving in their water of crystallization. When they are heated past the melting point and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By pressing on a metal disc within the heating pad, a nucleation centre is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The bond-forming process of crystallization is exothermic.[12][13] The latent heat of fusion is about 264–289 kJ/kg.[11] Unlike some types of heat packs, such as those dependent upon irreversible chemical reactions, sodium acetate heat packs can be easily reused by dissolving the crystals in boiling water for a few minutes until the crystals are completely dissolved.[14]

Preparation[edit]

A crystal of sodium acetate trihydrate (length 1.7 centimetres)

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 of variable concentration acetic acid, commonly known in its 5–8% solution as vinegar, with sodium carbonate ("washing soda"), sodium bicarbonate ("baking soda"), or sodium hydroxide ("lye"). Any of these reactions produce sodium acetate and water. When a sodium and carbonate ion-containing compound is used as the reactant, the carbonate anion is displaced from sodium bicarbonate or carbonate, as is the monatomic hydrogen from the hydroxide in acetic acid, forming the intermediate carbonic 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.

CH3COOH + NaHCO3 → CH3COONa + H2CO
3
H2CO
3
CO
2
+ H
2
O

Industrially, sodium acetate is prepared from glacial acetic acid and sodium hydroxide.

CH3COOH + NaOH → CH3COONa + H2O

Reactions[edit]

Sodium acetate can be used to form an ester with an alkyl halide such as bromoethane:

CH3COONa + BrCH2CH3CH3COOCH2CH3 + NaBr

Caesium salts catalyze this reaction.

References[edit]

  1. ^ a b c http://chemister.ru/Database/properties-en.php?dbid=1&id=1510
  2. ^ Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand. 
  3. ^ a b c d e f http://chemister.ru/Database/properties-en.php?dbid=1&id=172
  4. ^ a b c Sigma-Aldrich Co., Sodium acetate. Retrieved on 2014-06-07.
  5. ^ a b Acetic acid, sodium salt in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 2014-05-25)
  6. ^ Acetic acid, sodium salt, hydrate (1:1:3) in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 2014-05-25)
  7. ^ Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0. 
  8. ^ "Potato Chip Flavoring Boosts Longevity Of Concrete". Science Daily. 8 August 2007. 
  9. ^ Jungbunzlauer - General Information
  10. ^ [Courty JM, Kierlik E, Les chaufferettes chimiques, Pour la Science, décembre 2008, p 108-110]
  11. ^ a b Ibrahim Dincer and Marc A. Rosen. Thermal Energy Storage: Systems and Applications, page 155
  12. ^ "Crystallization of Supersaturated Sodium Acetate". Journal of Chemical Education. 
  13. ^ Fake latent heat and supersaturation
  14. ^ "How do sodium acetate heat pads work?". HowStuffWorks. Retrieved 2007-09-03. 

External links[edit]