Sodium acetate

Sodium acetate

Names
IUPAC name Sodium acetate
Systematic IUPAC name Sodium ethanoate
Other names Hot ice (Sodium acetate trihydrate)
Identifiers
CAS Number	127‑09‑3 6131‑90‑4 (trihydrate)
ChEBI	CHEBI:32954
ChEMBL	ChEMBL1354
ChemSpider	29105
EC Number	204-823-8
Jmol 3D model	Interactive image
PubChem	517045
RTECS number	AJ4300010 (anhydrous) AJ4580000
UNII	NVG71ZZ7P0
InChI InChI=1S/C2H4O2.Na/c1-2(3)4;/h1H3,(H,3,4);/q;+1/p-1 Key: VMHLLURERBWHNL-UHFFFAOYSA-M InChI=1/C2H4O2.Na/c1-2(3)4;/h1H3,(H,3,4);/q;+1/p-1 Key: VMHLLURERBWHNL-REWHXWOFAT
SMILES [Na+].[O-]C(=O)C
Properties
Chemical formula	C2H3NaO2
Molar mass	82.03 g·mol^−1
Appearance	White deliquescent powder
Odor	Vinegar (acetic acid) odor when heated to decomposition[1]
Density	1.528 g/cm^3 (20 °C, anhydrous) 1.45 g/cm^3 (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
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)[3]
Solubility	Soluble in alcohol, hydrazine, SO2[4]
Solubility in methanol	16 g/100 g (15 °C) 16.55 g/100 g (67.7 °C)[4]
Solubility in ethanol	Trihydrate: 5.3 g/100 mL
Solubility in acetone	0.5 g/kg (15 °C)[4]
Acidity (pKa)	24 (20 °C)[4] 4.76 CH3COOH[5]
Basicity (pKb)	9.25
Refractive index (nD)	1.464
Structure
Crystal structure	Monoclinic
Thermochemistry
Specific heat capacity (C)	100.83 J/mol·K (anhydrous)[6] 229 J/mol·K (trihydrate)[7]
Std molar entropy (S^o298)	138.1 J/mol·K (anhydrous)[6] 262 J/mol·K (trihydrate)[2]
Std enthalpy of formation (ΔfH^o298)	-709.32 kJ/mol (anhydrous)[4] -1604 kJ/mol (trihydrate)[2]
Gibbs free energy (ΔfG˚)	-607.7 kJ/mol (anhydrous)[4]
Pharmacology
ATC code	B05XA08 (WHO)
Hazards
Main hazards	Irritant
Safety data sheet	External MSDS
NFPA 704	1 1 0
Flash point	>250 °C (482 °F; 523 K) [5]
Autoignition temperature	600 °C (1,112 °F; 873 K)[5]
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Sodium acetate, CH₃COONa, also abbreviated NaOAc,^[8] also known as sodium ethanoate, is the sodium salt of acetic acid. This colorless deliquescent salt has a wide range of uses.

Applications

Industrial

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

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.^[9]

Food

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,^[10] given the E-number E262. It is often used to give potato chips a salt and vinegar flavor.

Buffer solution

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

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 136.4 °F/58 °C^[11] (to 137.12 °F/58.4 °C),^[12] 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 center is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The bond-forming process of crystallization is exothermic.^[13][14] 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, 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]

Preparation

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 acetic acid, commonly in the 5–8% solution known 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 from sodium bicarbonate or carbonate, reacts with hydrogen from the carboxyl group (-COOH) in acetic acid, forming 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
2O

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

CH₃COOH + NaOH → CH₃COONa + H₂O

Reactions

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

CH₃COONa + BrCH₂CH₃ → CH₃COOCH₂CH₃ + NaBr

Caesium salts catalyze this reaction.

References

1. "Sodium Acetate". International Chemical Safety Cards. National Institute of Occupational Safety and Health.
2. http://chemister.ru/Database/properties-en.php?dbid=1&id=1510
3. Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand.
4. http://chemister.ru/Database/properties-en.php?dbid=1&id=172
5. Sigma-Aldrich Co., Sodium acetate. Retrieved on 2014-06-07.
6. 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)
7. 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)
8. Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0.
9. "Potato Chip Flavoring Boosts Longevity Of Concrete". Science Daily. 8 August 2007.
10. Jungbunzlauer - General Information
11. Ibrahim Dincer and Marc A. Rosen. Thermal Energy Storage: Systems and Applications, page 155
12. [Courty JM, Kierlik E, Les chaufferettes chimiques, Pour la Science, décembre 2008, p 108-110]
13. "Crystallization of Supersaturated Sodium Acetate". Journal of Chemical Education.
14. Fake latent heat and supersaturation
15. "How do sodium acetate heat pads work?". HowStuffWorks. Retrieved 2007-09-03.

External links

• Hot Ice – Instructions, Pictures, and Videos

Salts and the ester of the Acetate ion
AcOH																	He
LiOAc	Be(OAc)2 BeAcOH											B(OAc)3	ROAc	NH4OAc	AcOAc	FAc	Ne
NaOAc	Mg(OAc)2											Al(OAc)3 ALSOL Al(OAc)2OH	Si	P	S	ClAc	Ar
KOAc	Ca(OAc)2	Sc(OAc)3	Ti(OAc)4	VO(OAc)3	Cr(OAc)2	Mn(OAc)2 MnAc3	Fe(OAc)2 FeAc3	Co(OAc)2, CoAc3	Ni(OAc)2	Cu(OAc)2	Zn(OAc)2	Ga(OAc)3	Ge	As	Se	BrAc	Kr
RbOAc	Sr(OAc)2	Y(OAc)3	Zr(OAc)4	Nb	Mo(OAc)2	Tc	Ru	Rh2(OAc)4	Pd(OAc)2	AgOAc	Cd(OAc)2	In	Sn(OAc)2 SnAc4	Sb(OAc)3	Te	IAc	Xe
CsOAc	Ba(OAc)2		Hf	Ta	W	Re	Os	Ir	Pt(OAc)2	Au	Hg2(OAc)2, HgAc2	TlOAc Tl(OAc)3	Pb(OAc)2 Pb(OAc)4	Bi(OAc)3	Po	At	Rn
Fr	Ra		Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Fl	Uup	Lv	Uus	Uuo
		↓
		La(OAc)3	Ce(OAc)x	Pr	Nd	Pm	Sm(OAc)3	Eu(OAc)3	Gd(OAc)3	Tb	Dy(OAc)3	Ho(OAc)3	Er	Tm	Yb(OAc)3	Lu(OAc)3
		Ac	Th	Pa	UO2(OAc)2	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr