The sodium acetate is a sodium salt of acetic acid whose molecular formula is CtwoH3ORtwoNa. It consists of a deliquescent white powder, essentially present in two forms: anhydrous and trihydrated. Both are very soluble in water, the universal solvent; but not so soluble in alcohols or acetone.
The anhydrous form has a density, a melting point and a boiling point with higher values than those presented by the trihydrate form of sodium acetate. This is because the water molecules interfere between the interactions of the Na ions.+ and CH3COO-.
Sodium acetate is stable, especially when stored between 2 and 8 ° C; but it is susceptible to the action of strong oxidizing agents and halogens.
It can be prepared by the reaction of sodium bicarbonate with acetic acid. Also, with the reaction of acetic acid with sodium hydroxide. Both reactions are simple to produce and inexpensive; the first can even be done at home.
This salt is a low toxic compound. Produces skin irritation, only after frequent and continuous contact. It is mildly irritating to the eyes but can irritate the respiratory tract. There is no information about a harmful effect of ingestion..
It has numerous uses and applications, highlighting its pH buffering function, along with acetic acid. The acetate buffer has a pKa = 4.7; which confers high efficiency in pH regulation in an acidic environment with pH values between 3 and 6.
Due to its low toxicity and its properties, it has been widely used to enhance the flavor of food, as well as an agent that provides protection against spoilage due to its action against microbes..
Article index
The image above shows the ions that make up anhydrous sodium acetate crystals (without water). The purple sphere corresponds to the Na cation+, and the molecular ion to its left is acetate, CH3COO-, with its oxygen atoms represented by red spheres.
These pairs, according to the formula CH3COONa, are in a 1: 1 ratio; for each CH anion3COO-, there must be a Na cation+ attracted to its negative charge and vice versa. Thus, the attractions between them, and the repulsions between equal charges, end up establishing structural patterns that define a crystal, whose minimum expression is the unit cell.
Said unit cell, like the crystal as a whole, varies depending on the arrangement of the ions in space; it is not always the same, even for the same crystalline system. For example, anhydrous sodium acetate can form two orthorhombic polymorphs, one of which is depicted below:
Note the arrangement of the ions: four CH ions3COO- they lock up a Na+ in such a way that they "draw" a distorted square-based pyramid. Each of these ch3COO- in turn they interact with another Na+ adjacent.
Sodium acetate has a high affinity for water; in fact, it is deliquescent, that is, it retains moisture until it dissolves in it. The higher the humidity, the sooner it "melts". This is because both the CH3COO- like Na+ can hydrate, surround themselves with water molecules that orient their dipoles towards their charges (Na+ Ohtwo, CH3COO- HOH).
When this salt is prepared in the laboratory or at home, its affinity for water is such that even at normal temperatures it is already obtained as a hydrate; the CH3COONa 3HtwoO. Its crystals stop being orthorhombic and become monoclinic, since they now incorporate three water molecules for each CH pair3COO- and Na+.
-Sodium acetate.
-Sodium ethanoate (IUPAC).
-Anhydrous: 82.03 g / mol.
-Trihydrate: 136.03 g / mol.
Deliquescent white powder.
To vinegar when heated to decomposition.
-Anhydrous: 1.528 g / cm3 at 20 ºC.
-Trihydrate: 1.45 g / cm3 at 20 ºC.
-Anhydrous: 324ºC (615ºF, 597K).
-Trihydrate: 58 ºC (136 ºF, 331 K).
-Anhydrous: 881.4ºC (1,618.5ºF, 1,154.5K).
-Trihydrate: 122 ° C (252 ° F, 395 K). It decomposes.
-Anhydrous: 123.3 g / 100 mL at 20ºC.
-Trihydrate: 46.4 g / 100 mL at 20 ºC.
16 g / 100 g at 15 ºC.
5.3 g / 100 mL (trihydrate).
0.5 g / kg at 15 ° C.
pKa: 24 (20 ºC).
pKb: 9.25. Here it is evidenced that sodium acetate is a basic salt because it has pKb less than its pKa.
1,464
-100.83 J / mol K (anhydrous).
-229.9 J / mol K (trihydrate).
Above 250ºC.
600 ºC.
8.9 (0.1 M solution at 25 ° C).
Stable. Incompatible with strong oxidizing agents and halogens. Sensitive to humidity.
Sodium acetate can form an ester by reacting with an alkyl halide; for example, bromoethane:
CH3COONa + BrCHtwoCH3 => CH3COOCHtwoCH3 + NaBr
Sodium acetate decarboxylates to methane (pyrolysis) in the presence of NaOH:
CH3COONa + NaOH => CH4 + NatwoCO3
The reaction is catalyzed by cesium salts.
Sodium acetate can be produced cheaply in the laboratory by reacting sodium bicarbonate with acetic acid:
NaHCO3 + CH3COOH => CH3COONa + HtwoCO3
This reaction is accompanied by the presence in the solution of an intense bubbling, due to the decomposition of carbonic acid in water and carbon dioxide..
HtwoCO3 => HtwoO + COtwo
Industrially, sodium acetate is produced by reacting acetic acid with sodium hydroxide.
CH3COOH + NaOH => CH3COONa + HtwoOR
Sodium acetate is used to manufacture thermal bags.
Initially, the salt crystals are dissolved in a volume of water to prepare a solution that becomes supersaturated..
Then the solution is heated to a temperature higher than 58 ºC, which is its melting point. The supersaturated solution is allowed to cool to room temperature and crystal formation is not observed; the solution is supercooled.
The absence of crystals is explained by the fact that the molecules of the liquid are too disordered and do not have the proper orientation to reach the crystallization temperature. The liquid is in a metastable state, a state of imbalance.
Given the instability of the supercooled liquid, any disturbance is sufficient to initiate crystallization. In the case of thermal bags, a mechanical attachment is pressed to stir the liquid and initiate the formation of crystals and the solidification of the sodium acetate trihydrate solution..
As crystallization occurs, the temperature increases. Sodium acetate trihydrate crystals take on the appearance of ice, but they are hot, which is why it is called "hot ice.".
-Sodium acetate is used in the textile industry as a mordant in the fabric dyeing process
-Neutralizes sulfuric acid waste
-It is used in the processing of cotton for the production of cotton pads, usable in personal cleaning and for medical purposes
-It is used in the pickling of metals, prior to their chrome plating
-Collaborates so that chloroprene vulcanization does not occur in the synthetic rubber production process
-Intervenes in the purification of glucose
-It is used in leather tanning.
Sodium acetate is one of the compounds used to supply electrolytes given to patients intravenously..
It is used to correct sodium levels in hyponatremic patients, also in the correction of metabolic acidosis and alkalinization of the urine..
It is used as a pH regulator in many enzymatic reactions that occur between pH 3 and pH 6.
The different pH of the acetate buffer solution are reached by the variation of the concentration of acetic acid and sodium acetate..
Thus, for example, to obtain a pH of 4.5, the buffer solution has an acetic acid concentration of 3.8 g / L and an anhydrous sodium acetate concentration of 3.0 g / L.
The concentration of the acetate buffer can be increased, increasing in the same proportion the components of the solution necessary to obtain the desired pH.
Acetate / acetonitrile buffer is used in capillary electrophoresis in the separation of photoberberines.
-Sodium acetate is a weak nucleophilic agent used in the anionic polymerization of β-lactone.
-It is used as a reagent in the nuclear magnetic resonance of biological macromolecules.
-It is used in the extraction of DNA from cells. Sodium is a cation that interacts with the negative charges of phosphates present in DNA, which helps in their condensation. In the presence of ethanol, DNA forms a precipitate that can then separate into the aqueous layer.
-Helps prevent bacterial growth, in addition to preventing the generation of excess acidity that causes food spoilage, thus maintaining a specific pH.
-The sodium present in acetate enhances the taste of food.
-Sodium acetate is used in the preparation of pickled vegetables: cucumber, carrot, onion, etc. In addition, it is used in the preservation of meat.
Concrete is damaged by the action of water, which shortens its duration. Sodium acetate acts as a concrete sealing agent that makes it waterproof, prolonging its initial characteristics.
A simple experiment is the synthesis of sodium acetate by reacting sodium bicarbonate with vinegar (5% acetic acid).
30 mL of vinegar is placed in a beaker and approximately 3.5 g of bicarbonate are added..
Sodium acetate and carbonic acid are formed in the reaction. Acid breaks down into carbon dioxide and water. The generation of carbon dioxide will produce an intense bubbling within the solution.
To collect the sodium acetate, the water evaporates, heating the solution.
Another simple experiment is the formation of crystals of sodium acetate trihydrate.
To do this, about 20 g of sodium acetate trihydrate are weighed and placed in a beaker, then 10 mL of water is added. The solution is heated to a temperature above 58 ºC.
Sodium acetate is completely dissolved to ensure that the solution is supersaturated. Previously, a Pietri dish is placed on a cold surface.
The contents of the beaker with the acetate trihydrate are slowly poured into the Pietri dish. The temperature of the liquid in the capsule begins to drop, even below the melting point, without observing the crystallization or solidification of the sodium acetate trihydrate..
Usually to produce crystallization of the sodium acetate trihydrate a small amount of the salt is added to serve as the crystallization core. Other times a small disturbance of the solution occurs, to initiate the crystallization of sodium acetate.
Sodium acetate trihydrate crystals have the appearance of ice, but if you touch them you will notice that they are relatively hot. For this reason, salt is called "hot ice".
Sodium acetate is a very low toxic compound. It is also not classified as a sensitizer for the skin and respiratory tract..
Additionally, sodium acetate is not classified as a germ cell mutagenic, carcinogen, or reproductive toxic agent..
In short, it is slightly irritating to the eyes. The respiratory tract can be irritated after inhalation. Frequent and constant contact with the skin can cause irritation.
Yet No Comments