Sodium sulfite, also known as Na2SO3, is a white crystalline powder that is commonly used as a preservative in the food industry and as a reducing agent in photography.
| IUPAC Name | Disodium sulfite |
| Molecular Formula | Na2SO3 |
| CAS Number | 7757-83-7 |
| Synonyms | Sodium sulfite; Disodium sulfite; Sulfurous acid, disodium salt; Sodium sulfonate; Sodium sulphite |
| InChI | InChI=1S/2Na.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 |
Sodium Sulfite Properties
Sodium Sulfite Formula
The chemical formula for sodium sulfite is Na2SO3. It is composed of two Na+ ions and one SO32- ion. The Na+ ions carry a positive charge while the SO32- ion carries a negative charge. Sodium sulfite is an ionic compound that forms a white crystalline powder.
Sodium Sulfite Molar Mass
The molar mass of Na2SO3 is 126.04 g/mol. This value is obtained by adding the atomic masses of each element in the compound. The atomic masses of sodium, sulfur, and oxygen are 22.99 g/mol, 32.06 g/mol, and 15.99 g/mol respectively. The molar mass is an important parameter used in stoichiometric calculations and can also be used to determine the amount of substance present in a sample.
Sodium Sulfite Boiling Point
Na2SO3 has a relatively high boiling point of 1650 °C. This is because of the strong ionic bonds between the Na+ and SO32- ions, which require a large amount of energy to break. The boiling point is the temperature at which a substance changes from a liquid to a gas phase. At this temperature, the vapor pressure of the liquid equals the atmospheric pressure.
Sodium Sulfite Melting Point
The melting point of Na2SO3 is 33.4 °C. This relatively low melting point is due to the weak intermolecular forces between the Na2SO3 molecules. When heated, the intermolecular forces are overcome, and the solid Na2SO3 melts into a liquid.
Sodium Sulfite Density g/mL
The density of Na2SO3 is 2.633 g/mL. Density is defined as the mass of a substance per unit volume. The high density of Na2SO3 is due to its ionic nature and the presence of two sodium ions per sulfite ion in its structure.
Sodium Sulfite Molecular Weight
The molecular weight of Na2SO3 is 126.04 g/mol. This value is obtained by adding the atomic weights of each element in the compound. The molecular weight is an important parameter used in stoichiometric calculations and can also be used to determine the amount of substance present in a sample.
Sodium Sulfite Structure
Na2SO3 has a crystalline structure with two Na+ ions and one SO32- ion arranged in a repeating pattern. The Na+ ions are arranged in a face-centered cubic lattice, while the SO32- ions occupy the octahedral sites within the lattice. The ionic bonds between the Na+ and SO32- ions result in a stable crystalline structure.
Sodium Sulfite Solubility
Na2SO3 is highly soluble in water, with a solubility of 22.4 g/100 mL at 20°C. This high solubility is due to the ionic nature of Na2SO3, which allows it to dissociate in water and form Na+ and SO32- ions. The solubility of Na2SO3 in water increases with temperature, as the kinetic energy of the molecules increases and more ions are released into the solution.
| Appearance | White crystalline powder |
| Specific Gravity | 2.633 g/cm³ |
| Color | Colorless to white |
| Odor | Odorless |
| Molar Mass | 126.04 g/mol |
| Density | 2.633 g/mL |
| Melting Point | 33.4 °C |
| Boiling Point | 1650 °C |
| Flash Point | Not applicable |
| Water Solubility | Highly soluble |
| Solubility | Soluble in glycerol, slightly soluble in ethanol |
| Vapor Pressure | 0 mmHg at 20 °C |
| Vapor Density | Not applicable |
| pKa | 6.35 |
| pH | 8.3 – 9.5 (5% solution) |
Sodium Sulfite Safety and Hazards
Na2SO3 can be hazardous if not handled properly. It can cause skin and eye irritation, and if ingested, it can lead to nausea, vomiting, and abdominal pain. It may also cause respiratory irritation if inhaled. In addition, Na2SO3 may react with other chemicals and produce toxic gases, such as sulfur dioxide, which can be harmful to health. As such, it is important to wear appropriate personal protective equipment when handling Na2SO3, and to avoid exposure to the eyes, skin, and mucous membranes. Na2SO3 should also be stored in a cool, dry, and well-ventilated area, away from incompatible materials.
| Hazard Symbols | Xi, O |
| Safety Description | Avoid contact with skin and eyes. In case of contact, rinse immediately with plenty of water and seek medical advice. Do not ingest. Avoid inhalation of dust. Wear appropriate personal protective equipment. Keep away from heat, sparks, and flames. |
| UN ID | 1384 |
| HS Code | 283210 |
| Hazard Class | 8 – Corrosive substances |
| Packing Group | III |
| Toxicity | LD50 (oral, rat) – 1,640 mg/kg; LC50 (inhalation, rat) – 63 mg/m³ |
Sodium Sulfite Synthesis Methods
Various methods can synthesize Na2SO3.
One common method involves reacting sodium hydroxide with sulfur dioxide gas in the presence of water. The reaction produces Na2SO3 and water as byproducts.
In another method, sodium carbonate reacts with sulfur dioxide gas in the presence of water, producing Na2SO3 and carbon dioxide gas. To increase the yield of Na2SO3, one can carry out this reaction at elevated temperatures and pressures.
The reaction of sodium bisulfite with sodium hydroxide can synthesize Na2SO3. This reaction produces Na2SO3, water, and sodium chloride as byproducts.
Another method involves reacting sodium sulfide with sulfur dioxide gas in the presence of water to produce Na2SO3 and hydrogen sulfide gas.
To synthesize Na2SO3, one must treat sodium sulfate with sulfur dioxide gas in the presence of a reducing agent, such as activated carbon. This reaction produces Na2SO3 and carbon dioxide gas.
Each of these methods has its own advantages and disadvantages, and the choice of method depends on various factors, such as the desired yield, purity, and cost of the product, as well as the availability of reagents and equipment.
Sodium Sulfite Uses
Na2SO3 has several important industrial and commercial uses, including:
- Photography: Used as a reducing agent and preservative in photographic developing solutions. It helps to stabilize the image and prevent fading.
- Water treatment: Used to remove chlorine and excess oxygen from water in industrial and municipal water treatment plants. It also helps to prevent the corrosion of pipes and equipment.
- Paper and pulp industry: Used in the production of paper and pulp to bleach and reduce the lignin content of the pulp. This helps to improve the quality and color of the paper.
- Food industry: Used as a preservative and antioxidant in the food industry. It helps to prevent discoloration and spoilage of foods, such as dried fruits, wine, and beer.
- Textile industry: Used as a reducing agent and bleach in the textile industry to remove excess dye and improve the colorfastness of fabrics.
- Chemical industry: Used as a reducing agent in various chemical reactions, such as in the production of dyes, pharmaceuticals, and polymers.
- Other uses: Also used in the manufacture of detergents, leather products, and personal care products, such as hair coloring agents and shampoos.
Questions:
Q: What is the normal sodium sulfite in a boiler?
A: The normal Na2SO3 concentration in a boiler is typically between 20 and 40 parts per million (ppm), depending on the operating pressure and other factors.
Q: How to balance sulfur dioxide with sodium hydroxide to form sodium sulfite and water?
A: To balance the equation for the reaction of sulfur dioxide and sodium hydroxide to form Na2SO3 and water, you would need to ensure that there are equal numbers of atoms of each element on both sides of the equation. The balanced equation would be SO2 + 2NaOH → Na2SO3 + H2O.
Q: What is sodium sulfite?
A: Na2SO3 is a white crystalline compound that is commonly used in various industrial and commercial applications, such as photography, water treatment, paper production, and food preservation.
Q: What is the formula for sodium sulfite?
A: The formula for sodium sulfite is Na2SO3.
Q: Is sodium sulfite a base?
A: Na2SO3 is a salt of a strong base (sodium hydroxide) and a weak acid (sulfurous acid) and therefore has basic properties. However, it is not typically considered a strong base.
Q: Is sodium sulfite stable in water?
A: Na2SO3 is relatively stable in water, but it can gradually decompose over time, especially in the presence of oxygen or other oxidizing agents.
Q: Is sodium sulfite flammable?
A: Na2SO3 is not flammable, but it may react with certain oxidizing agents and release sulfur dioxide gas, which is a respiratory irritant and can be flammable.
Q: Where to buy sodium sulfite locally?
A: Na2SO3 can be purchased from chemical supply companies, industrial suppliers, and some specialty retailers. It may also be available at some local hardware stores or home improvement centers.
Q: What foods contain sodium sulfite?
A: Na2SO3 is commonly used as a preservative in foods such as wine, beer, dried fruits, and some processed meats.
Q: What product is equal to sodium sulfite?
A: Sodium bisulfite is a similar compound that can be used as a substitute for Na2SO3 in some applications. Other substitutes may include sodium metabisulfite or potassium metabisulfite.