Sodium acetate

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Sodium acetate
Sodium acetate by No Tears Only Dreams Now.jpg
Crystals of sodium acetate trihydrate.
Names
IUPAC name
Sodium acetate
Systematic IUPAC name
Sodium ethanoate
Other names
Hot ice (Sodium acetate trihydrate)
Properties
C2H3O2Na
CH3COONa (anhydrous)
CH3COONa·3 H2O (trihydrate)
Molar mass 82.03 g/mol
Appearance Hygroscopic solid
Odor Odorless
Acetic (at high temp.)
Density 1.528 g/cm3 (20 °C, anhydrous)
1.45 g/cm3 (20 °C, trihydrate)
Melting point Anhydrous:
324 °C (615 °F; 597 K)
Trihydrate:
58 °C (136 °F; 331 K)
Boiling point Anhydrous:
881.4 °C (1,618.5 °F; 1,154.5 K) (decomposes)
Trihydrate:122 °C (252 °F; 395 K) (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)
Solubility Soluble in ethanol, hydrazine, liq. SO2
Solubility in acetone 0.05 g/100 g (15 °C)
Solubility in ethanol Trihydrate:
5.3 g/100 ml
Solubility in methanol 16 g/100 g (15 °C)
16.55 g/100 g (67.7 °C)
Acidity (pKa) 24 (20 °C)
4.76 CH3COOH
Thermochemistry
138.1 J·mol-1·K-1 (anhydrous)
262 J·mol-1·K-1 (trihydrate)
−709.32 kJ/mol (anhydrous)
−1,604 kJ/mol (trihydrate)
Hazards
Safety data sheet Sigma-Aldrich (anhydrous)
Sigma-Aldrich (trihydrate)
Flash point 250 °C (482 °F; 523 K)
Lethal dose or concentration (LD, LC):
3,530 mg/kg (rat, oral)
Related compounds
Related compounds
Acetic acid
Calcium acetate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sodium acetate is the sodium salt of acetic acid, with the chemical formula CH3COONa. It forms a white or translucent powder or crystals that have a variety of uses in the home lab.

Properties

Chemical

Sodium acetate is most commonly seen as a buffering agent for acetic acid solutions. Pure, anhydrous sodium acetate and other acetates may be dry-distilled to yield acetone, though this may not be economical. Though calcium acetate is more often considered, sodium acetate may potentially be combined with concentrated sulfuric acid and then distilled to yield nearly glacial acetic acid, a highly sought-after chemical. Finally, sodium acetate can be reacted with primary haloalkanes, such as chloromethane, to yield an alkyl acetate ester and a sodium salt containing the respective halogen. That esterification is catalyzed by caesium salts.

Physical

Sodium acetate typically exists as an anhydrous white crystalline powder or as thin, transparent crystals of the trihydrate. When produced using household vinegar, solutions and crystals of sodium acetate may appear golden or amber in color. Sodium acetate has an odor resembling that of vinegar, though slightly more fruity and pleasant. The taste and low toxicity of this compound allow it to be used as a salt-and-vinegar-type flavoring agent in some foods.

Sodium acetate trihydrate supercools easily and will crystallize on contact with a sufficient nucleation site, such as another crystal of sodium acetate or sodium bicarbonate.

Availability

Though not commonly found in stores, sodium acetate is easily produced from two common household chemicals: vinegar and baking soda.

Some if not most type of heat pads contain a supersaturated solution of sodium acetate.

Preparation

Sodium acetate can be crystallized from a solution in which sodium bicarbonate, carbonate, or hydroxide was combined with an equal or excess of acetic acid (distilled white vinegar will work if high purity is not vital). This is the very same reaction behind the common "baking soda volcano" science experiments that produce a voluminous foam of sodium acetate and carbon dioxide.

The main problem with using even the purest vinegar is that distilled vinegar is not pure acetic acid, as there are plenty of extra organics. Distilling the vinegar beforehand produces pure acetic acid. However, obtaining concentrated acetic acid from vinegar via distillation is not easy and requires several distillations to remove the water that also distills due to their close boiling points.

Projects

Handling

Safety

Pure sodium acetate, as well as sodium acetate produced in a sterile environment from vinegar, is of very low toxicity and is even safe to season food with in reasonable quantities (though this usage is not recommended with lab grade chemicals).

Storage

Sodium acetate should be stored in closed bottles. The anhydrous form should be stored in sealed bottles.

Disposal

Sodium acetate has very little toxicity and doesn't require any special disposal. However, because is a sodium salt it's recommended to avoid dumping it on grass or other plants, as it will kill it. It can however be used as a (weak) weedkiller.

References

Relevant Sciencemadness threads