Whether you source chemicals for a municipal water treatment plant, a gold mine in India, or a food processing facility, understanding the properties of sodium metabisulfite is critical to making safe, cost-effective, and performance-driven procurement decisions. Sodium metabisulfite (Na2S2O5, CAS 7681-57-4) is a versatile inorganic sulfite used globally for dechlorination, cyanide detoxification, food preservation, pulp bleaching, and textile anti-chlorine treatment. Yet many buyers overlook how the product’s chemical identity, solubility, stability, and purity directly impact dosage, handling, and final application outcomes. This guide breaks down the essential physical and chemical properties, explains how sodium metabisulfite is made, compares it with sodium bisulfite, and provides practical usage directions—all from the perspective of a procurement manager or process engineer sourcing industrial-grade material.
To use the product effectively, you must first know its core properties. Sodium metabisulfite is a white to yellowish crystalline powder with a pungent sulfur dioxide odor. It is freely soluble in water (54 g/100 mL at 20°C) and slightly soluble in alcohol. The aqueous solution is acidic, with a pH around 4.0–5.5 for a 5% solution, due to the release of sulfurous acid. On a molecular level, sodium metabisulfite is the disodium salt of disulfurous acid (H2S2O5), meaning each molecule contains two sulfur atoms bridged through an S–S bond, which distinguishes it from simple sulfites.
Key physical constants: molecular weight 190.11 g/mol; melting point >150°C with decomposition; apparent density approx. 1.1–1.3 g/cm³. When heated above 150°C, it decomposes, releasing sulfur dioxide (SO2) and leaving sodium sulfite (Na2SO3) and sulfate residues. This thermal behavior is important if your process involves drying or exposure to high temperatures.
The properties of sodium metabisulfite that matter most in industrial use are its strong reducing action in aqueous media and its ability to generate SO2 under acidic conditions. In water, it dissociates into sodium (Na⁺) and metabisulfite ions (S2O52−), which further hydrolyze to bisulfite (HSO3−) and sulfite (SO32−) species. This equilibrium gives it excellent reactivity for removing chlorine, oxygen, and heavy metal oxidants. The high assay (97–98% Na2S2O5 for Hailei Chemical’s food and industrial grades) ensures low iron (≤10 ppm), heavy metals (≤5 ppm as Pb), and minimal insoluble matter, meeting EU, FCC, and USP standards for critical applications.
Understanding the production pathway helps buyers evaluate supply chain consistency and impurity profiles. Sodium metabisulfite is manufactured by reacting sulfur dioxide (SO2) with a sodium base—typically sodium carbonate (soda ash) or sodium hydroxide (caustic soda)—under controlled aqueous conditions. The process can be summarized in two main steps:
High-quality producers—like Hailei Chemical—use food-grade sulfur and purified water, ensuring the final product meets both industrial and food-grade specifications. The choice of sodium source influences residual alkalinity: soda ash yields a product with slightly higher sodium carbonate traces, while NaOH route gives a purer bisulfite intermediate but requires tighter process control. Knowing this helps you request the right certificate of analysis (CoA) for your specific purity and particle size needs.
A common point of confusion is the relationship between sodium bisulfite (NaHSO3) and sodium metabisulfite. While both are sulfite-based reducing agents, their chemical structure and practical behavior differ. Sodium bisulfite is a monoprotic salt of sulfurous acid, typically existing only in aqueous solution or as a labile solid. Sodium metabisulfite, on the other hand, is the dehydrated dimer of sodium bisulfite: two bisulfite ions lose one water molecule to form the S–S bonded metabisulfite. When dissolved in water, sodium metabisulfite hydrolyzes to sodium bisulfite and then to sulfite species, so the active chemistry is often similar. However, there are key practical differences:
For most procurement scenarios involving solid sulfite chemicals, sodium metabisulfite offers better shelf life and concentration. Always verify which form your process actually requires; switching from a liquid bisulfite to dry metabisulfite can cut logistics costs significantly but may require dissolving equipment.
Proper usage hinges on matching the properties of sodium metabisulfite to your process chemistry. Below we cover general guidelines for four key sectors.
In municipal and industrial water treatment, sodium metabisulfite is used to neutralize free chlorine and chloramines before discharge or membrane protection. The stoichiometric reaction is: Na2S2O5 + 3 Cl2 + 5 H2O → 2 NaHSO4 + 6 HCl. Typically, 1.34 mg of pure Na2S2O5 removes 1 mg of Cl2. Because commercial product is ~97% pure, a safety factor of 1.1–1.2 is used. A 10% solution is prepared and dosed via metering pump. Stirring and contact time of 5–15 minutes assure complete dechlorination. Online ORP sensors can automate the feed rate.
In gold leaching operations, residual cyanide must be destroyed to meet tailings discharge limits. Sodium metabisulfite provides SO2 gas in the well-known INCO process, oxidizing cyanide to cyanate. A typical usage rate is 5–10 kg metabisulfite per ton of ore depending on cyanide concentration. A 20% solution is injected into tailings slurry along with copper sulfate catalyst, at pH 8–9, with vigorous air sparging. The technical-grade sodium metabisulfite with high purity and low iron is essential to avoid precipitates that clog nozzles.
As an E223 additive, sodium metabisulfite inhibits enzymatic browning in dried fruits, wines, and vegetable preserves. Dosage varies: 200–500 ppm SO2 equivalent in wine must, or dipping solutions of 1–2% w/v for sliced apples and potatoes. Always use food-grade material that meets FCC/USP standards, free from arsenic and heavy metals. Important: sodium metabisulfite is an allergen; final products must declare sulfite content if above 10 ppm.
In pulp and paper mills, metabisulfite solutions (5–10%) remove residual chlorine-based bleach from pulp before papermaking, preventing yellowing and fiber damage. In textile finishing, it serves as an anti-chlor agent after hypochlorite bleaching to neutralize excess chlorine before dyeing. For both, a gentle reducing environment (pH 4–6, ambient temperature) works best.
India is one of the largest import markets for sodium metabisulfite due to its booming water treatment, mining, and food sectors. If you are searching for a sodium metabisulfite supplier in India, you need a partner who combines consistent product quality with logistics expertise. Hailei Chemical exports bulk sodium metabisulfite to major Indian ports (Nhava Sheva, Chennai, Mundra) in 25 kg woven bags, 1000 kg supersacks, or custom packaging. Our 97–98% purity with low heavy metals and iron aligns with BIS and food additive standards, while our logistical support—including full customs documentation, REACH compliance data, and pre-shipment samples—simplifies your import process.
When qualifying any international supplier, request a detailed CoA showing not just Na2S2O5 assay but also iron, arsenic, selenium, and chloride content. Scrutinize the product’s physical properties like bulk density and particle size distribution (typically 40–120 mesh) if your process uses dry feeders. Hailei Chemical’s technical team can provide specification sheets tailored to your application, ensuring the properties of sodium metabisulfite you receive precisely match your needs.
It is an acidic salt. A 5% aqueous solution has a pH of about 4.0–5.5 due to the formation of sulfurous acid. This mild acidity makes it ideal for reducing environments without drastically altering process pH.
Yes, in many applications. Sodium metabisulfite releases sulfite ions upon dissolution. The main advantage is higher SO2 equivalent per kilogram and better dry stability. However, for some food or pharmaceutical processes requiring precise sodium sulfite, direct substitution should be validated.
Store in a cool, dry, well-ventilated area away from acids and oxidizers. Sealed bags prevent moisture absorption, which would trigger decomposition and caking. Under proper conditions, shelf life exceeds 12 months without significant loss of SO2 content.
A simple iodometric titration determines available SO2 content. If the assay has dropped below your required threshold (e.g., 97%), the product may have degraded due to moisture ingress. Hailei Chemical uses quality-controlled packaging to maintain assay throughout transit.
When sourcing a bulk supply of sodium metabisulfite, having a deep grasp of its properties—from solubility and pH to redox behavior and impurity limits—empowers you to optimize processes and avoid costly misapplications. Whether you need food-grade powder for fruit preservation or industrial-grade crystals for cyanide destruction, our sodium metabisulfite product page provides full specifications and order options. To discuss your volume, packaging, or documentation requirements with our technical sales team, request a competitive quote today.
When procurement managers type “buy sodium bisulfite” into a search engine, they often mean sodium metabisulfite—a distinct chemical with the formula Na2S2O5 and CAS 7681-57-4. This common mix-up can lead to ordering the wrong chemical, causing costly application failures in water treatment, gold mining, and food preservation. At Hailei Chemical, we help industrial buyers clarify this confusion and source high-purity sodium metabisulfite with the exact specifications their process demands.
The similarity in names and overlapping applications make it easy to confuse sodium bisulfite (NaHSO3) with sodium metabisulfite (Na2S2O5). While both are sulfite compounds that release sulfur dioxide (SO2) in acidic conditions, they are chemically distinct and supplied in different forms.
In water, sodium metabisulfite dissolves and hydrolyzes to form sodium bisulfite ions. This chemical behavior explains why the two chemicals are often used interchangeably—and why a search for “buy sodium bisulfite” frequently leads to metabisulfite suppliers.
Ordering the incorrect form can disrupt operations. If your process calls for a dry, easy-to-handle powder with high active SO2 content, sodium metabisulfite is the correct choice. Accidentally receiving a liquid bisulfite solution may compromise dosing accuracy, increase freight costs, or introduce unwanted water into a water-sensitive reaction. For mining, food, and textile applications, the solid sodium metabisulfite (industrial-grade sodium metabisulfite) with a purity of 97–98% is the industry standard.
Many industries depend on sodium metabisulfite’s reducing power. Below are the main sectors where your “buy sodium bisulfite” query should lead you straight to a quality metabisulfite.
Municipal water treatment plants and industrial process water systems use sodium metabisulfite to neutralize residual chlorine and chloramines. The reaction is instantaneous and produces harmless sulfate and chloride ions. Typical dosing: 1.4 mg of sodium metabisulfite per 1 mg of chlorine. The solid powder format makes it easy to prepare stock solutions or feed directly via dry feeders.
In gold extraction, sodium metabisulfite is employed to detoxify cyanide tailings before discharge. The sulfite air (SO2/air) process uses metabisulfite as the SO2 source to oxidize cyanide to cyanate, significantly reducing environmental toxicity. Mining chemical buyers rely on consistent, high-purity metabisulfite to meet strict environmental compliance.
Food-grade sodium metabisulfite is a widely permitted preservative (E223) in the winemaking, dried fruit, and seafood industries. It inhibits microbial growth, prevents enzymatic browning, and acts as an antioxidant. For winemakers, it provides both free and bound SO2 to protect wines during aging. If your recipe calls for “sodium bisulfite,” confirm with your supplier that solid food-grade sodium metabisulfite food grade is the correct input.
After bleaching with chlorine-based agents, textiles are treated with an “anti-chlor” to remove residual chlorine that could weaken fibers. Sodium metabisulfite is the preferred chemical because it decomposes excess hypochlorite without leaving corrosive residues, thereby preserving fabric strength and whiteness.
In the paper industry, sodium metabisulfite serves as a reductive bleaching agent for mechanical pulp. It brightens fibers without degrading cellulose, and it acts as a dechlorination agent after chlorine dioxide bleaching stages. The solid metabisulfite provides a stable, high-purity SO2 source that integrates seamlessly into existing chemical dosing systems.
Understanding the manufacturing process helps buyers assess product quality and impurities. Sodium metabisulfite is produced by passing sulfur dioxide gas through an aqueous slurry of sodium carbonate or sodium hydroxide. The exothermic reaction forms sodium bisulfite, which upon concentration and cooling crystallizes as sodium metabisulfite. The chemical steps are:
The resulting crystals are centrifuged, dried, and sieved to produce the free-flowing white powder that is packed in 25 kg bags, 1000 kg supersacks, or custom packaging. Leading manufacturers control heavy metals, iron, and arsenic to meet food-grade specifications (e.g., FCC, JECFA) or technical-grade requirements.
One of the most researched properties is sodium metabisulfite solubility in water because dosing efficiency depends on it. Sodium metabisulfite is highly soluble:
When dissolved, it releases SO2, so solutions are moderately acidic (pH 4.0–5.5 at 10% w/w). For industrial use, a 5–20% stock solution is typically prepared in stainless steel or HDPE tanks. Ensure adequate ventilation because dissolved SO2 can off-gas, especially in warm environments. For continuous dechlorination, metering pumps must be calibrated to account for solution strength and temperature-dependent solubility.
If you are preparing a laboratory solution for analytical or medical use (such as the sickling test), always use fresh distilled water and an airtight container to prevent premature oxidation of the sulfite to sulfate.
Though sodium metabisulfite is versatile, specific process conditions may call for an alternative reducing agent. Here are common scenarios where exploring a sodium metabisulfite alternative makes sense.
Sodium metabisulfite slightly lowers pH. In applications requiring strictly neutral pH (e.g., sensitive reverse osmosis membranes), ascorbic acid (vitamin C) is a viable alternative. It quenches chlorine without altering pH and is fully biodegradable, but it is more expensive and less stable in solution.
In boiler water treatment, sodium sulfite (Na2SO3) or catalyzed sulfite are often preferred over metabisulfite because they are designed for high-temperature oxygen removal and scale inhibition. Sodium metabisulfite could be used, but its SO2 release profile differs.
Food producers who need to minimize sodium content may switch to potassium metabisulfite (E224), which provides an equivalent amount of SO2 per mole but with potassium instead of sodium. This is particularly relevant in low-sodium preserved foods.
In large-scale industrial operations like sugar refining or certain mining processes, compressed SO2 gas can be more economical than solid metabisulfite. However, gas handling requires significant safety infrastructure.
Despite these alternatives, sodium metabisulfite remains the most cost-effective solid sulfite for the majority of dechlorination, preservation, and anti-chlorine tasks due to its high active SO2 content (typically 65% available SO2) and ease of transport.
While Hailei Chemical primarily serves industrial sectors, laboratory and medical customers also inquire about preparing sodium metabisulfite solutions for the sickling test—a diagnostic assay for sickle cell disease. The standard protocol requires a 2% (w/v) sodium metabisulfite solution.
How to prepare sodium metabisulfite for sickling test:
Our food-grade and analytical-grade sodium metabisulfite maintains low heavy-metal profiles, making it suitable for critical laboratory applications where impurities could interfere with test results.
Whether your initial search is “buy sodium bisulfite” or “sodium metabisulfite supplier,” evaluating the following parameters will ensure you receive the right product.
Weifang Hailei Fine Chemical Co., Ltd. has decades of experience exporting high-purity sodium metabisulfite to buyers in over 50 countries. Our product, CAS 7681-57-4, delivers a consistent 97–98% purity (higher for food grade) and is backed by comprehensive documentation—COA, MSDS, and third-party test reports. Whether you need full container loads for a mining operation or smaller batches for a food processing plant, our logistics team ensures on-time delivery with the correct UN-compliant packaging.
We understand that many of our customers initially search for “buy sodium bisulfite.” Our team is ready to clarify specifications and provide exactly the sulfite chemical your process requires.
Make the right choice for your water treatment, gold mining, food preservation, or textile application. Request a quote today and let our experts support your supply chain with reliable, technical-grade or food-grade sodium metabisulfite.
When sourcing chemicals for large-scale industrial operations, every specification matters — and sodium metabisulfite density g/ml is a parameter that directly impacts logistics, storage design, and process accuracy. Whether you are a procurement manager for a water treatment plant, a mining chemicals buyer, or a laboratory technician preparing a sickling test solution, understanding the physical properties of this compound is essential for cost-effective and safe handling. In this comprehensive guide, we detail the density, molecular weight, solubility, and other key properties of sodium metabisulfite (Na2S2O5), compare it with sodium bisulfite, and explain how these data points influence your purchasing decisions.
Sodium metabisulfite is a white or yellowish crystalline powder with a density of approximately 1.48 g/cm³ (equivalent to 1.48 g/ml). While this value might seem like a minor technical detail, it carries significant weight in several areas of industrial supply and usage.
Bulk orders are priced by weight, but the physical volume they occupy depends on density. With a bulk density typically ranging from 1.1 to 1.3 g/cm³ in loose fill, a 25 kg bag of sodium metabisulfite occupies about 19–23 liters. For a full container load of 20 metric tons, understanding the exact density allows logistics teams to plan container space, predict stacking loads, and calculate freight costs accurately. A higher settled density can mean more product per pallet, reducing the per-kilogram transportation expense.
In industrial water treatment or gold mining cyanide detoxification, sodium metabisulfite is dissolved into water to create a reducing agent solution. Operators frequently dose by weight, but if they must meter by volume, knowing the sodium metabisulfite density g/ml of the solid allows conversion from mass to volume for automatic feeding systems. This ensures the correct concentration of active SO2 is delivered to the process stream, avoiding under-dosing that compromises treatment or over-dosing that wastes chemicals and handling costs.
Density also influences flow properties. Sodium metabisulfite with consistent particle size distribution and adequate density flows freely from silos and big bags, minimizing bridging and rat-holing in hoppers. When sourcing, industrial buyers should request a certificate of analysis that not only confirms purity (97-98%) but also reports bulk density, as this relates directly to material handling performance.
To fully evaluate a chemical supplier, buyers must look beyond the price per ton. The following table compiles the essential physical and chemical data for sodium metabisulfite that appear on every professional specification sheet.
| Property | Value |
|---|---|
| Chemical formula | Na2S2O5 |
| CAS number | 7681-57-4 |
| Molecular weight | 190.1 g/mol |
| Appearance | White to yellowish crystalline powder |
| Odor | Slight sulfur dioxide odor |
| Density (solid) | 1.48 g/cm³ (1.48 g/ml) at 20 °C |
| Bulk density (loose) | 1.1–1.3 g/cm³ |
| Melting point | Decomposes above 150 °C |
| Solubility in water | 540 g/L at 20 °C |
| pH (5% solution) | 3.5–5.0 |
| Purity (commercial grade) | 97–98% min |
The molecular weight of sodium metabisulfite (190.1 g/mol) is a fundamental constant used in stoichiometric calculations. For example, in cyanide destruction at gold mines, one mole of sodium metabisulfite can theoretically neutralize two moles of cyanide when catalyzed by copper sulfate. Using the molecular weight, engineers calculate exact dosage rates: to treat 1 kg of free cyanide, approximately 3.66 kg of pure sodium metabisulfite is required. Any deviation in purity must be factored in, which is why a reliable, high-purity supply (97–98%) from a consistent source like our sodium metabisulfite product page reduces operational guesswork.
Industrial buyers often encounter both sodium bisulfite and sodium metabisulfite in the market. While they are chemically related and can be used interchangeably in many applications, their physical properties and handling characteristics differ significantly — and understanding these differences can lead to smarter sourcing decisions.
Sodium bisulfite (NaHSO3) is typically supplied as a liquid solution, whereas sodium metabisulfite is a dry powder. When dissolved in water, sodium metabisulfite quickly hydrolyzes to form sodium bisulfite, releasing sulfur dioxide in the process:
Na2S2O5 + H2O → 2 NaHSO3
This means solid sodium metabisulfite offers higher active SO2 content per unit weight – about 65% by weight – compared to commercial liquid bisulfite solutions that are often diluted to 20–40% concentration. For long-distance shipping or for operations in remote locations, purchasing dry sodium metabisulfite is far more economical. Buyers looking to buy sodium bisulfite in solid form actually need sodium metabisulfite, as true solid bisulfite is unstable. We encourage you to review the specifications and packaging options to see which product matches your logistics needs.
Beyond heavy industry, sodium metabisulfite also serves a critical biomedical role — in the sickling test used to diagnose sickle cell disease or trait. Laboratories rely on a freshly prepared reducing solution, and the preparation method directly affects test reliability. Knowing how to prepare sodium metabisulfite for sickling test ensures accurate results and avoids false negatives.
The most common protocol uses a 2% weight/volume sodium metabisulfite solution. To prepare:
In this application, the sodium metabisulfite density g/ml of the powder is irrelevant for mass-based measurement, but it is critical if a lab technician attempts to scoop by volume. A level teaspoon may yield anywhere from 4 to 6 grams depending on compaction, leading to concentration errors. Always use a calibrated balance. High-purity material (≥97%) is recommended to avoid interference from sulfates or thiosulfates that could affect the sickle cell deformation response. Industrial suppliers like Hailei Chemical can provide analytical-grade or food-grade material that meets laboratory requirements when a dedicated medical-grade product is not available.
Securing a reliable supply of sodium metabisulfite goes beyond meeting the minimum purity. The following factors, all tied to physical and chemical properties, should be on every buyer’s checklist.
Sodium metabisulfite is available in food grade (generally ≥98% purity, low heavy metals) and industrial/technical grade (≥97%). For food preservation and winemaking, food grade is non-negotiable. For water treatment and gold processing, industrial grade suffices but must have consistent assay values and minimal insoluble matter. Always request a certificate of analysis showing actual assay, iron content, and heavy metals.
As highlighted, sodium metabisulfite density and particle size distribution affect dissolution rate and handling. A supplier that double-crystallizes the product tends to produce a free-flowing, low-dusting powder with uniform density — a significant advantage in automated feeding systems. Verify that bulk density falls within the expected 1.1–1.3 g/cm³ range and that no caking occurs during transportation.
Exposure to moisture and air causes sodium metabisulfite to oxidize to sulfate, reducing its effectiveness. Top suppliers package the product in 25 kg polyethylene-lined bags or 1000 kg bulk bags with airtight sealing, sometimes under nitrogen. Ask about the packaging specifications and expected shelf life. Hailei Chemical’s sodium metabisulfite product specifications include detailed packaging information and storage recommendations.
Sodium metabisulfite is classified as a hazardous material (UN 3260, class 8) due to corrosive properties when wet. Knowledgeable suppliers provide msds, transport documentation, and assist with customs clearance for international shipments. Dimensional weight calculations for air freight or LCL sea freight depend on the container volume, which is directly tied to the product’s density. Confirming the exact sodium metabisulfite density g/ml from your supplier prevents costly miscalculations.
If your process allows use of a liquid reducing agent, you might also explore whether to buy sodium bisulfite solution locally to avoid dissolving solid powder on site. However, for high-volume operations where shipping water is inefficient, solid sodium metabisulfite remains the most cost-effective choice. Hailei Chemical offers both grades and can assist with a technical comparison to help you determine the best fit.
Sodium metabisulfite has a true density of 1.48 g/cm³, which is the same as 1.48 g/ml. This value represents the mass of the solid crystal per unit volume, without void spaces. The bulk density, which includes air gaps between granules, is lower — typically 1.1–1.3 g/cm³.
The molecular weight (190.1 g/mol) is used to convert between mass and moles in chemical reactions. For example, to determine how much sodium metabisulfite is needed to dechlorinate 1 kg of chlorine, you use the molar ratio and the molecular weight to find the required mass in grams.
Yes, in aqueous solutions they behave identically because sodium metabisulfite hydrolyzes to sodium bisulfite. Solid sodium metabisulfite is a convenient, stable source of bisulfite and is often the preferred form for industrial and laboratory use.
The 2% sodium metabisulfite solution should be prepared fresh daily. Its reducing power decreases over time, and using an oxidized solution may produce false-negative results in the sickling test.
Store in a cool, dry, well-ventilated area away from acids and oxidizers. Keep bags sealed and off the floor. If the product absorbs moisture, it can cake and clump, altering the bulk density and making handling difficult. Under proper conditions, shelf life is typically 12–24 months.
From the sodium metabisulfite density g/ml that dictates container utilization, to the molecular weight that anchors high-precision dosing calculations, the physical properties of this versatile chemical are far from trivial data points — they are the keys to cost savings, operational safety, and product performance. Whether you are sourcing for a mining operation in Africa, a municipal water plant in Southeast Asia, or a food processing facility, partnering with a supplier that understands these details makes all the difference.
At Weifang Hailei Fine Chemical Co., Ltd., we provide sodium metabisulfite in food grade and industrial grade with consistent purity and documented physical specifications. Our technical team is ready to answer your questions about density, packaging, or any other parameter relevant to your application.
Ready to secure a stable supply? Request a quote today and download our latest product datasheet. For detailed parameters, visit our sodium metabisulfite product page.