Sodium acetate salt, or simply sodium acetate, has many practical uses. It is the conjugate base of a weak acid, meaning that it only partially ionizes when dissolved in water. This provides sodium acetate with buffering properties, that is the ability to maintain solutions at a relatively constant pH despite acid or base challenges. This property along with its low toxicity, helps explain why sodium acetate can be found in industries ranging from petroleum production to food flavoring.
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Chemically, sodium acetate contains one sodium or Na atom, two carbon or C atoms, two oxygen or O atoms, and 3 hydrogen or H atoms for every one molecule of sodium acetate. While technically the formula can be represented as C2H3NaO2, this version fails to provide much information other than the component atoms. To better understand the chemistry, a more instructive representation looks like CH3COONa. In this case, the arrangement of the atoms in the formula illustrates the presence of an acetate or CH3COO- group and the balancing sodium or Na cation. The molecular weight of sodium acetate is 82.03 g/mole. Synonyms of sodium acetate include: sodium acetate anhydrous, sodium ethanoate, sodium ethanoate anhydrous, acetic acid sodium salt, ethanoic acid sodium salt and natrium aceticum.
Physically, sodium acetate appears as a white hygroscopic or water-attracting crystalline powder. The pure substance has a melting point of 58 degrees C or 136 degrees F, and completely decomposes at the boiling point of 120 degrees C or 248 degrees F. Sodium acetate dissolves readily in water, having a solubility of 500 g/L at 20 degrees C. Crystals have a basic pH of about 7.5 to 9.0.
The safety of sodium acetate has been studied extensively in rat and mouse animal models. When given orally, the lethal dose that will kill half a population of rats is 3530mg of sodium acetate per kg of rat body weight. If inhaled rather than ingested, the dose required to kill half the rat population is much higher, over 30 g/m3 per hour. In mice, a subcutaneous or under the skin injection of 3200mg/kg of body weight will kill half of a mouse population, similar to the ingestion of sodium acetate in rats. However, orally mice can withstand much more than rats; the lethal dose for half the population of mice being 6891mg/kg of body weight. In humans, inhalation of sodium acetate may cause a cough and sore throat. Direct skin or eye contact may cause redness and irritation. However, overall, toxicity in humans is minimal.
Homemade Sodium Acetate
Sodium acetate can be made with the common household ingredients baking soda and vinegar. Wear safety goggles as the splashing of solutions into your eyes can be irritating. Baking soda or sodium bicarbonate and vinegar or acetic acid react to form sodium acetate along with carbon dioxide and water. To begin the reaction, add one heaping spoonful of baking soda to a glass container. Slowly add vinegar, being careful not to create too much foam. Keep adding vinegar while stirring the mixture. Once the mixture stops bubbling, you can stop adding vinegar as all of the sodium bicarbonate has converted to sodium acetate, carbon dioxide -- which are the bubbles you saw -- and water. To separate out the sodium acetate from the water, boil the solution until you hear a sizzling and popping sound. At this point, if you blow across the top of the surface, crystals will form. When you get this super-saturated sodium acetate solution, cool the solution to room temperature; it will form a translucent gel. Scrape the gel into a bowl lined with a coffee filter, which will absorb any remaining water. Break up the pieces with the back of a spoon and put them on another coffee filter to finish the drying process, creating sodium acetate powder.
Sodium acetate finds use in an extremely diverse range of industries. In the textile industry, sodium acetate neutralizes sulfuric acid waste streams and improves the wearing quality of finished fabrics. In photography, sodium acetate constitutes part of the developer solution and acts as a photo resist agent. In rubber production, sodium acetate retards vulcanization helping control the overall process. Sodium acetate added to foods acts as a preservative, and a flavoring agent. In particular, potato chips with sodium acetate have a distinctive "salt and vinegar" taste. Sodium acetate and acetic acid solutions act as buffers to maintain relatively constant pH, a property useful both for biochemical research reactions, the petroleum industry and in the cosmetic industry. In the medical field, sodium acetate solutions treat patients with high blood acid levels and/or low sodium levels.
REFERENCES & RESOURCES
- Chemical Land 21: Sodium Acetate
- ChemBlink: Sodium Acetate
- Material Safety Data Sheet: Sodium Acetate
- Instructables.com: How to Make Sodium Acetate from Household Ingredients
- KidsHealth.org: Sodium Acetate
- Merriam-Webster.com: Hygroscopic
- PesticideInfo.org: Sodium Acetate
- MubyChem Group: Sodium Acetate