Gourt Home::Gourt :: Sodium acetate
| Sodium acetate | |
| General | |
|---|---|
| Chemical formula | 3 |
| Appearance | white solid |
| CAS number | 127-09-3 (anhydrous) 6131-90-4 (trihydrate) |
| Physical | |
| Molecular weight | 82.034 amu (136.080 for trihydrate) |
| Melting point | decomposes at 597 K (324 °C) |
| Boiling point | n/a |
| Density | 1.45 g/cm³ |
| Crystal structure | orthorhombic |
| Solubility | 76 g/100 g of water |
| Thermochemistry | |
| ΔfH0gas | -? |
| ΔfH0liquid | ? |
| ΔfH0solid | ? |
| S0gas, 1 bar | ? |
| S0liquid, 1 bar | ? |
| S0solid | ? |
| Safety | |
| Ingestion | Large doses may cause abdominal pain, nausea and vomiting. |
| Inhalation | May cause irritation, with symptoms of coughing, sore throat, labored breathing, and chest pain. |
| Skin | May cause irritation (redness and/or pain). |
| Eyes | Chronic exposure may cause irritation, redness and pain. |
| SI units and standard conditions used unless otherwise stated. | |
- Textile industry: to neutralize sulphuric acid and as a resist to aniline dyes
- Leather industry: as a pickling agent in chrome tanning
- Chemical industry: in the manufacture of diazo compounds
- Paper industry: as a buffering agent
- Rubber industry: to retard vulcanization of chloroprene (see neoprene)
- Food industry: as a food preservative with E number E262
- As a medium in chemical heat reservoirs
The last usage is seen in consumer heating pads. When these pads are solid, they are composed of sodium acetate trihydrate, or hydrated crystals of sodium acetate. If the solid is heated to the boiling point of water, the water molecules will be released from the crystals. This freed water can then dissolve the sodium acetate. After cooling, the sodium acetate remains dissolved even though the solution is supersaturated.
This means that the energy that was required to release the water molecules from the crystals and dissolve the sodium acetate into that water still remains in the system even though the temperature has dropped. The clicking of a disk within the pad triggers the crystallization of the sodium acetate trihydrate. When the crystals form, the energy that was required to initially dissolve them is then released. This release of energy raises the temperature to 54°C. For the above reasons, this is technically not a demonstration of the heat that is released during a phase change. It is an exothermic chemical reaction. The process is theoretically repeatable indefinitely, although the containing pouch will eventually break in practice. [http://www.atmos.washington.edu/2003Q3/101/demonstrations/fake_latentheat_supersaturation.html
Reactions
Sodium acetate can be used as a reagent to form an ester using an alkyl halide such as bromoethane.
H3C-COO- Na+ + Br-CH2-CH3 → H3C-COO-CH2-CH3 + NaBr
Synthesis of sodium acetate
Sodium acetate can be obtained easily by the reaction of acetic acid with sodium bicarbonate.
H3C-COOH + Na+*- → H3C-COO- Na+ + H2CO3
The resulting carbonic acid decomposes quickly to carbon dioxide and water so the equilibrium is pushed to the right. This is the well-known "fizzing" reaction between baking soda and vinegar. By subsequently boiling off most of the water, one can refine either a concentrated solution of sodium acetate or actual crystals. However (like most reactions) the baking soda and vinegar must be combined in exact proportions to avoid excess acid or bicarbonate in the final product if preparing a solution. For preparing crystals, if there is an excess of acetic acid, the acetic acid would be easily driven off, but not an excess of sodium bicarbonate.
See also
External links
"Sodium acetate"