Sodium acetate is the sodium salt of acetic acid. It has the chemical formula C2H3O2Na and is also known as sodium ethanoate. It is an inexpensive chemical that has a wide range of uses, including as a food additive and pickling agent or a laboratory reagent. It is also the prime ingredient in portable, reusable, chemical-based heating packs.
Sodium acetate is added to food to help prevent bacterial growth. As an acid, it acts as a neutralizing agent for basic or alkaline foods and can also act as a buffer to help maintain a specific pH. The sodium can also be used to enhance flavors. Unlike many food additives, sodium acetate has no known adverse effects.
Pickling is method of preserving food that not only stops or greatly slows down spoiling caused by microorganisms, but it is a food preservation method that can also enhance flavor. The use of sodium acetate in pickling is similar to its use as a more simple food additive, but picking uses sodium acetate in much greater quantities and for longer periods of time. Essentially, food to be pickled, such as a cucumber, is soaked in an acid solution. This imparts a very salty or sour taste. The salty taste comes from the sodium ions, and the sour taste comes from the acetate ions, the ion of acetic acid.
Sodium acetate is a very common reagent used in molecular biology and biochemistry labs, among others. Colorado State University notes that researchers use it to extra DNA from cells. The positive sodium cations bind to the negative phosphate charges on the DNA, helping the DNA to condense. In the presence of ethanol, or similar alcohol, DNA forms a precipitate that can then be separated from the aqueous layer.
Sodium acetate neutralizes the very strong sulfuric acid found in waste streams. It can be used in certain photography processes, helping impart a particular pattern of coating on surfaces. On metallic surfaces, it can help remove impurities, stains, rust or scale and can also aid in the tanning process of leather, as well as cure chloroprene, a synthetic rubber product.
Those chemical heating pads or hand warmers that you can find at the drug store consist of a supersaturated solution of sodium acetate in water. Manufacturers place a flat, notched, metal disc in the solution. Flexing or moving the disk releases a very small amount of crystals of sodium acetate that have adhered to the disk. These crystals then start a chain reaction of crystallization with the rest of the sodium acetate. This reaction occurs quickly, releasing a lot of energy stored in the sodium acetate crystal framework. When the sodium acetate molecules crystallize, forming a solid, heat is released.
The pad is reusable as the sodium acetate can return to the supersaturated liquid state by soaking the heating pad in boiling water and then allowing it to slowly cool to room temperature. During the process, a small amount of sodium acetate crystals will reform on the notched ferrous disk, while the rest of the sodium acetate will exist in the supersaturated liquid state, ready to be reactivated.