Sodium metabisulfite (Na2S2O5) is a chemical compound used as a preservative and antioxidant in food and beverages. It can also be used as a disinfectant and bleaching agent in various industries.
| IUPAC Name | Sodium pyrosulfite |
| Molecular Formula | Na2S2O5 |
| CAS Number | 7681-57-4 |
| Synonyms | Disodium disulfite, Pyrosulfurous acid, disodium salt, Sodium pyrosulphite, Sodium disulfite |
| InChI | InChI=1S/2Na.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2 |
Sodium Metabisulfite Properties
Sodium Metabisulfite Formula
The chemical formula of sodium metabisulfite is Na2S2O5. It is composed of two sodium ions (Na+) and one disulfite ion (S2O5-2). The compound is a white or yellowish crystalline powder that is soluble in water and has a pungent odor.
Sodium Metabisulfite Molar Mass
The molar mass of Na2S2O5 is 190.107 g/mol. This value is calculated by adding the atomic masses of the elements in the compound, which are 22.99 g/mol for sodium, 32.06 g/mol for sulfur, and 15.99 g/mol for oxygen. The molar mass is an important property that helps in determining the amount of a substance needed in a chemical reaction.
Sodium Metabisulfite Boiling Point
Na2S2O5 has a high melting point of 150 °C, but it decomposes before it can boil. The compound breaks down into sulfur dioxide (SO2) and sodium sulfite (Na2SO3) at a temperature of around 150 °C. Therefore, the boiling point of Na2S2O5 is not applicable.
Sodium Metabisulfite Melting Point
The melting point of Na2S2O5 is 150 °C. At this temperature, the compound undergoes a phase change from a solid to a liquid. The melting point is an important physical property that helps in identifying and characterizing a substance.
Sodium Metabisulfite Density g/mL
The density of Na2S2O5 is 1.48 g/mL. It is a relatively dense compound that sinks in water. The density of a substance is the mass per unit volume and is an important physical property that helps in determining the amount of a substance in a given volume.
Sodium Metabisulfite Molecular Weight
The molecular weight of Na2S2O5 is 190.107 g/mol. It is the sum of the atomic weights of all the atoms in the compound. Molecular weight is an important property that helps in calculating the amount of a substance needed in a chemical reaction.
Sodium Metabisulfite Structure
Na2S2O5 has a crystalline structure and belongs to the orthorhombic crystal system. The crystal lattice is made up of sodium ions and disulfite ions arranged in a repeating pattern. The compound has a tetrahedral molecular geometry, with the sulfur atoms at the center of the tetrahedron.
Sodium Metabisulfite Solubility
Na2S2O5 is highly soluble in water, with a solubility of 54 g/100 mL at 25 °C. It is also soluble in glycerol and slightly soluble in ethanol. The solubility of a substance is an important property that determines its ability to dissolve in a given solvent.
| Appearance | White or yellowish crystalline powder |
| Specific Gravity | 1.48 |
| Color | White to yellowish |
| Odor | Pungent |
| Molar Mass | 190.107 g/mol |
| Density | 1.48 g/mL |
| Melting Point | 150 °C |
| Boiling Point | Decomposes before boiling |
| Flash Point | Not applicable |
| Water Solubility | 54 g/100 mL at 25 °C |
| Solubility | Soluble in glycerol and slightly soluble in ethanol |
| Vapor Pressure | Not available |
| Vapor Density | Not available |
| pKa | 7.2 |
| pH | 4.5 (5% solution) |
Sodium Metabisulfite Safety and Hazards
Na2S2O5 can be hazardous if not handled properly. It is a strong reducing agent and can cause irritation to the skin, eyes, and respiratory system upon exposure. Ingestion of the compound can lead to severe gastrointestinal distress. Na2S2O5 should be stored in a cool, dry, and well-ventilated area away from incompatible materials. It should not be mixed with strong acids, strong oxidizers, or reducing agents. Protective equipment, such as gloves, goggles, and respiratory masks, should be used when handling the compound. Emergency measures, such as eye wash stations and fire extinguishers, should be readily available in case of accidents.
| Hazard Symbols | Xi (Irritant) |
| Safety Description | Avoid contact with skin and eyes. Wear protective clothing and gloves. Do not ingest. Use with adequate ventilation. |
| UN IDs | UN 2676 |
| HS Code | 2832.10.00 |
| Hazard Class | 8 (Corrosive substances) |
| Packing Group | III |
| Toxicity | LD50 (oral, rat): 1,000 mg/kg; LC50 (inhalation, rat): 11 mg/L (4 hours) |
Sodium Metabisulfite Synthesis Methods
One can synthesize Na2S2O5 through various methods, including reacting sodium bisulfite with sulfur dioxide in the presence of an oxidizing agent such as hydrogen peroxide. The process heats the adduct of sodium bisulfite and sulfur dioxide to form Na2S2O5.
Another method involves the reaction of sodium hydroxide with sulfur dioxide gas, followed by the addition of sulfuric acid to form sodium sulfate and Na2S2O5.
Another synthesis method involves the reaction of sodium carbonate with sulfur dioxide and then heating the resulting sodium sulfite in the presence of air. This process produces sodium sulfate and Na2S2O5.
In the presence of an oxidizing agent such as hydrogen peroxide or nitric acid, Na2S2O5 can be prepared by reacting sulfur with sodium sulfite.
In industry, the most common method of synthesizing Na2S2O5 is by the reaction of sodium bisulfite with sulfur dioxide in the presence of a catalyst such as manganese dioxide. Heating the sodium bisulfite/sulfur dioxide adduct forms Na2S2O5.
Sodium Metabisulfite Uses
Na2S2O5 has various uses across multiple industries due to its strong reducing properties and its ability to act as a preservative and antioxidant. Some of the common uses of Na2S2O5 include:
- Food and beverage industry: Widely used as a preservative and antioxidant in food and beverage products such as wine, beer, fruit juices, and dried fruits. It helps to prevent spoilage and oxidation of these products, thereby extending their shelf life.
- Pharmaceutical industry: Used as an antioxidant in various pharmaceutical products such as creams, ointments, and tablets. It helps to prevent the degradation of these products due to exposure to air and light.
- Water treatment: Used to dechlorinate water in water treatment plants. It helps to remove excess chlorine and chloramines, which can be harmful to aquatic life.
- Photography: Used as a photographic developer and fixer in the photography industry. It helps to reduce silver ions to metallic silver, thereby forming the photographic image.
- Textile industry: Used as a reducing agent in the textile industry for dyeing and printing processes. It helps to remove excess oxygen from the dyeing solution, thereby improving the color intensity and uniformity.
Questions:
Q: Where can I buy sodium metabisulfite locally?
A: Na2S2O5 can typically be found at chemical supply stores or online retailers. It may also be available at some specialty food stores, as it is commonly used as a preservative in the food industry.
Q: Where to buy sodium metabisulfite?
A: Na2S2O5 can be purchased from chemical supply stores or online retailers that specialize in chemicals. It may also be available at some specialty food stores.
Q: Is sodium metabisulfite safe?
A: Na2S2O5 can be hazardous if not handled properly. It is important to wear appropriate protective equipment and follow safety guidelines when handling this compound. It can cause skin and eye irritation, and can also release toxic sulfur dioxide gas if mixed with acid. However, when used in appropriate concentrations and handled with care, Na2S2O5 is generally considered safe for its intended uses.
Q: Can you turn sodium bisulfate into sodium metabisulfite?
A: Yes, sodium bisulfate (NaHSO4) can be converted to Na2S2O5 by heating it at high temperatures in the presence of an oxidizing agent, such as hydrogen peroxide. The reaction results in the release of water and the formation of Na2S2O5.
Q: What is the difference between sodium bisulfite and sodium metabisulfite?
A: The main difference between NaHSO3 and Na2S2O5 is their chemical structure. Sodium bisulfite has one sulfite group (-SO3) and one hydrogen ion (H+), while Na2S2O5 has two sulfite groups (-SO3) linked together. Na2S2O5 is also more stable and has a longer shelf life compared to sodium bisulfite.
Q: What is the oxidation number of S in Na2S2O5?
A: The oxidation number of sulfur (S) in Na2S2O5 is +5.
Q: How to find a concentration of IO3- from KIO3 and Na2S2O5?
A: The concentration of IO3- can be determined by titration with a known concentration of sodium thiosulfate (Na2S2O3), using starch as an indicator. The reaction between KIO3 and Na2S2O5 produces iodine (I2), which reacts with Na2S2O3 to form NaI and Na2S4O6. By measuring the volume of Na2S2O3 required to react with the iodine, the concentration of IO3- can be calculated.
Q: What ions are in Na2S2O5?
A: Na2S2O5 is composed of two sodium ions (Na+) and one disulfite ion (-S2O5).