Sodium sulfite plays an important role in many fields due to its strong reducing properties and special chemical properties. In chemical production, it is a key reducing agent, participating in the synthesis of insurance powder, helping the printing and dyeing industry to reduce the dyeing process; it is also a raw material for the preparation of sodium thiosulfate, used in the production of pharmaceutical intermediates and papermaking cooking agents. In the food industry, sodium sulfite is a commonly used food additive (INS No. 223), which can inhibit the activity of polyphenol oxidase in fruits and vegetables, prevent preserved fruits and dried vegetables from browning, and extend the shelf life; in the winemaking process, it can act as an antioxidant, eliminate the oxygen produced by fermentation, inhibit the growth of microorganisms, and maintain the stability of wine quality. In the field of environmental protection, it is a powerful assistant for flue gas desulfurization, reacting with sulfur dioxide to generate sodium bisulfite, converting sulfur oxides in industrial waste gas, and the desulfurization efficiency exceeds 85%; in wastewater treatment, it can reduce hexavalent chromium ions to trivalent chromium ions, so that heavy metal precipitation is removed. In addition, the pharmaceutical industry uses it to prepare drug intermediates such as vitamin C and antibiotics; the papermaking industry uses it as a lignin remover to reduce the lignin content of pulp and improve the whiteness and strength of paper. It is an indispensable basic chemical in industrial production.

The chemical properties of sodium sulfite (Na₂SO₃) are centered on reducing properties, and it has the typical characteristics of both salts and weak acid salts: Strong reducing properties are its most prominent properties. It is easily oxidized to sodium sulfate by oxygen in the air (2Na₂SO₃ + O₂ = 2Na₂SO₄). The solid will gradually turn into white powder after being left for a long time. When it encounters strong oxidants such as potassium permanganate, it can make the acidic potassium permanganate solution fade (5SO₃²⁻ + 2MnO₄⁻ + 6H⁺ = 5SO₄²⁻ + 2Mn²⁺ + 3H₂O). It is often used for redox titration in the laboratory. As a positive salt of sulfurous acid, it easily dissociates into Na⁺ and SO₃²⁻ in water. The aqueous solution is alkaline due to the hydrolysis of SO₃²⁻ (SO₃²⁻ + H₂O ⇌ HSO₃⁻ + OH⁻), with a pH of about 9~10. It can undergo double decomposition reaction with acid: it will release sulfur dioxide gas (Na₂SO₃ + H₂SO₄ = Na₂SO₄ + SO₂↑ + H₂O) when it encounters strong acid such as dilute sulfuric acid. This property is often used to prepare SO₂ in the laboratory; when it reacts with weak acid (such as acetic acid), it will generate bisulfite. In addition, sodium sulfite has complexing properties and can form complexes with certain metal ions. For example, it reacts with Ag⁺ to form a white silver sulfite precipitate. When in excess, the precipitate dissolves to form a [Ag (SO₃)₂]³⁻ complex ion; it can decompose into sodium sulfide and sodium sulfate at high temperatures, reflecting thermal instability. The diversity of its chemical properties enables it to play a role in redox reactions, acid-base neutralization and complex reactions, making it an important chemical in industry and laboratories.

When storing sodium sulfite, strict control must be exercised in terms of environment, packaging, and management to prevent changes in its properties or potential safety hazards. Since sodium sulfite has a strong reducing property and is easily oxidized by oxygen in the air, the storage environment must be dry and ventilated, away from humid areas, to prevent accelerated oxidation reactions after moisture. At the same time, it is necessary to avoid mixing with oxidants (such as potassium chlorate, potassium permanganate, etc.) to prevent violent redox reactions. When storing, it should be kept at a distance of at least 1 meter from such substances. The sealing of the packaging container is crucial. It should be packaged in sealed plastic barrels or iron barrels lined with polyethylene plastic bags to ensure that the packaging is not damaged to prevent oxygen and moisture from invading the air. For solid sodium sulfite, if the powder in the package is found to be agglomerated, it is necessary to check whether it has been oxidized and deteriorated in time. The storage place should also be away from fire and heat sources, the temperature should not exceed 30℃, the humidity should not exceed 75%, and it should be equipped with corresponding fire-fighting equipment and leakage emergency treatment equipment. In terms of management, a strict in-and-out registration system should be established to follow the "first in, first out" principle to avoid long-term backlogs. In addition, the storage area should be clearly marked to prohibit unauthorized personnel from entering. Operators should wear protective gloves and masks to prevent skin contact or inhalation of dust to ensure the safety and stability of the storage process.

Sodium sulfite has a dual effect on human health. Reasonable exposure and excessive exposure will have different consequences: As a food additive (such as limited use in wine and preserved fruit), when ingested in small amounts, sodium sulfite can be metabolized into sulfate in the body and excreted, and generally does not cause harm to health. However, for asthma patients, the sulfur dioxide gas it releases may induce bronchospasm and cause breathing difficulties. Such people should pay special attention to avoid contact with food or work environments containing sodium sulfite. In case of occupational exposure or accidental contact, acute toxicity is more prominent: inhalation of its dust will irritate the respiratory mucosa, causing coughing and sore throat. Long-term exposure to high concentrations of dust may cause chronic bronchitis; dust contact with the eyes will cause conjunctival congestion and pain. If not rinsed in time, it may damage the cornea. When the skin contacts solids or solutions, it may cause contact dermatitis, with symptoms such as redness, swelling, and itching. If there are wounds on the skin, sodium sulfite may also aggravate the irritation. Excessive intake can cause gastrointestinal reactions, such as nausea, vomiting, and abdominal pain, and in severe cases may cause gastric mucosal damage; its strong reducing properties will consume antioxidants in the body, and large doses may interfere with cell metabolism and even cause temporary damage to liver and kidney function. In addition, sodium sulfite easily generates sulfur dioxide gas under acidic conditions. If it is used in large quantities in confined spaces (such as kitchens), it may cause inhalation poisoning due to excessive gas concentrations, resulting in symptoms such as dizziness, headache, and difficulty breathing. Therefore, protection must be taken when contacting sodium sulfite, and national standards must be strictly observed when used in food to avoid excessive intake or occupational exposure.

The production method of sodium sulfite is mainly based on the absorption and neutralization reaction of sulfur dioxide. Combined with the source of raw materials and process characteristics, the common processes are as follows: The soda ash absorption method is the mainstream industrial process: the gas containing sulfur dioxide (such as sulfuric acid production tail gas, SO₂ produced by burning sulfur) is passed into the sodium carbonate solution, and a step-by-step reaction first occurs to generate sodium bisulfite (Na₂CO₃ + 2SO₂ + H₂O = 2NaHSO₃ + CO₂), and then soda ash is added to neutralize until the solution is neutral. After evaporation, concentration, cooling and crystallization, sodium sulfite crystals (2NaHSO₃ + Na₂CO₃ = 2Na₂SO₃ + CO₂↑ + H₂O) are obtained. The raw materials of this process are easy to obtain, and the sulfur dioxide absorption rate exceeds 95%, which is suitable for large-scale production. The sodium hydroxide neutralization method directly absorbs sulfur dioxide through caustic soda solution: first, SO₂ is passed into sodium hydroxide solution, and the pH value is controlled to generate sodium sulfite (2NaOH + SO₂ = Na₂SO₃ + H₂O), and then the product is obtained by evaporation, crystallization, and drying. This method has a fast reaction speed and high product purity (up to 97% or more), but the cost of caustic soda is relatively high, and it is mostly used to prepare high-purity sodium sulfite. In addition, there is the ammonium sulfite double decomposition method: ammonia reacts with sulfur dioxide to generate ammonium sulfite, which is then double-decomposed with sodium carbonate solution to generate sodium sulfite and ammonium carbonate, which are filtered and evaporated and crystallized to obtain the product. This process can utilize by-products of the nitrogen fertilizer industry to reduce costs, but the process is more complicated. During the production process, the reaction temperature (usually 40~80℃) and pH value (7~9) need to be controlled to avoid the generation of sodium bisulfite, and the sulfur dioxide in the tail gas is recovered to ensure that environmental protection standards are met.