Sodium acetate

Sodium acetate
IUPAC name	Sodium acetate
Systematic name	Sodium ethanoate
Other names	sodium salt
Identifiers
CAS number	127-09-3 Y, [6131-90-4] (trihydrate)
PubChem	517045
RTECS number	AJ4300010 (anhydrous) AJ4580000 (trihydrate)
ChemSpider ID	29105
Properties
Molecular formula	C2H3NaO2
Molar mass	82.03 g mol−1
Appearance	White deliquescent powder odorless
Density	1.528 g/cm3 1.45 g/cm3 (trihydrate)
Melting point	324 °C (anhydrous) 58 °C (trihydrate)
Boiling point	881.4 °C (anhydrous) 122 °C (trihydrate)
Solubility in water	76 g/100 ml (0°C)
Solubility	soluble in ethanol (5.3 g/100 mL (trihydrate)
Basicity (pKb)	9.25
Refractive index (nD)	1.464
Structure
Crystal structure	monoclinic
Hazards
MSDS	External MSDS
Main hazards	Irritant
NFPA 704	1 1 0
Flash point	250 °C
Autoignition temperature	607 °C
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium acetate, (also sodium ethanoate) is the sodium salt of acetic acid. It is an inexpensive chemical produced in industrial quantities for a wide range of uses.

Applications

Industrial

Sodium acetate is used in the textile industry to neutralize sulfuric acid waste streams, and as a photoresist while using aniline dyes. It is also a pickling agent in chrome tanning, and it helps to retard vulcanization of chloroprene in synthetic rubber production.

Food

Sodium acetate may be added to foods as a seasoning. It may be used in the form of sodium diacetate — a 1:1 complex of sodium acetate and acetic acid,^[1] given the E-number E262. A frequent use of this form is in salt and vinegar chips in the United States. Many US brands, including national manufacturer Frito Lay, sell "salt and vinegar flavored" chips that use this chemical, with lactose and smaller percentages of other chemicals, in lieu of a real salt and vinegar preparation.^[2]

Buffer solution

As the conjugate base of a weak acid, a solution of sodium acetate and acetic acid can act as a buffer to keep a relatively constant pH. This is useful especially in biochemical applications where reactions are pH dependent.

Heating pad

Sodium acetate is also used in consumer heating pads or hand warmers and is also used in hot ice. Sodium acetate trihydrate crystals melt at 58 °C, dissolving in their water of crystallization. When they are heated to around 100 °C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of supercooling to room temperature without forming crystals. By clicking on a metal disc in the heating pad, a nucleation center is formed which causes the solution to crystallize into solid sodium acetate trihydrate again. The bond-forming process of crystallization is exothermic, hence heat is emitted.^[3][4][5] The latent heat of fusion is about 264–289 kJ/kg.^[6] Unlike some other types of heat packs that depend on irreversible chemical reactions, sodium acetate heat packs can be easily recharged by boiling until all crystals are dissolved. Therefore they can be recycled indefinitely.^[7]

An inexpensive hand warmer containing a supersaturated solution of sodium acetate which releases heat on crystallization

Preparation

a crystal of sodium acetate trihydrate (length 1.7 centimeter)

Sodium acetate is inexpensive, and is usually purchased from chemical suppliers, instead of being synthesized in the laboratory. It is sometimes produced in a laboratory experiment by the reaction of acetic acid with sodium carbonate, sodium bicarbonate, or sodium hydroxide. These reactions produce aqueous sodium acetate, and water. Carbon dioxide is produced in the reaction with sodium carbonate and bicarbonate, and it leaves the reaction vessel as a gas (unless the reaction vessel is pressurized).

CH₃–COOH + Na⁺[HCO₃]^– → CH₃–COO^– Na⁺ + H₂O + CO₂

This is the well-known "volcano" reaction between baking soda and vinegar. 84 grams of sodium bicarbonate (baking soda) react with 750 ml of 8% vinegar to make 82 g sodium acetate in water. By boiling off most of the water, one can refine either a concentrated solution of sodium acetate or crystals.

Reactions

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

H₃C–COO^– Na⁺ + Br–CH₂–CH₃ → H₃C–COO–CH₂–CH₃ + NaBr

In such a reaction, the sodium acetate is usually complexed with caesium in order to increase the nucleophilicity of the carboxylate group.

References

External links

• Hot Ice – Instructions, Pictures, and Videos
• Sodium Acetate Experiment yields instant crystals