Description
Sodium sulfate is the inorganic compound with the chemical formula Na2SO4. It is a white, odorless, crystalline solid that is highly soluble in water. In its anhydrous (water-free) form, it’s known as the mineral thenardite. The decahydrate form, Na2SO4⋅10H2O, is commonly referred to as Glauber’s salt.
Chemical Properties
| Property | Anhydrous Sodium Sulfate (Na₂SO₄) | Sodium Sulfate Decahydrate (Na₂SO₄·10H₂O, Glauber’s Salt) |
| Chemical formula | Na₂SO₄ | Na₂SO₄·10H₂O |
| Molar mass | 142.04 g/mol | 322.20 g/mol |
| Appearance | White crystalline solid | White crystalline solid |
| Odor | Odorless | Odorless |
| Density | 2.664 g/cm³ | 1.464 g/cm³ |
| Melting point | 884 °C | 32.38 °C |
| Boiling point | 1,429 °C | — (decomposes before boiling) |
| Solubility in water | Highly soluble; temperature dependent | Highly soluble; temperature dependent |
| Solubility in ethanol | Insoluble | Insoluble |
| Crystal structure | Orthorhombic | Monoclinic |
Uses
Detergents and Cleaners: It is a key filler in powdered laundry detergents and other cleaning products. It dilutes the active ingredients, which helps reduce production costs and improves the powder’s free-flowing properties, preventing it from caking.
Pulp and Paper Industry: Sodium sulfate, often referred to as “salt cake,” is used in the Kraft process for turning wood into paper pulp. It helps break down lignin in the wood, making it easier to separate the cellulose fibers.
Glass Manufacturing: It is used in the production of glass to remove small air bubbles from the molten glass, ensuring a clear, high-quality final product.
Textile Industry: It acts as a leveling agent in textile dyeing, which helps the dye penetrate fabrics evenly and prevents uneven coloration or streaks.
Desiccant: The anhydrous form of sodium sulfate is a strong drying agent (desiccant) used in laboratories to remove water from organic liquids.
Major Grades of Sodium Sulfate
Industrial/Technical Grade: This is the most common and widely used grade. It is typically a high-purity product, often with a minimum of 99% Na2SO4. This grade is used in large-scale industrial processes where absolute purity is not the primary concern.Uses: As a filler in laundry detergents, as “salt cake” in the pulp and paper industry, as a fining agent in glass manufacturing, and in the textile industry as a leveling agent for dyeing.
Reagent Grade (ACS Grade): This grade is produced to meet the stringent specifications set by organizations like the American Chemical Society (ACS). It has a higher purity than industrial grade and is used for laboratory and analytical applications. It is often labeled with a purity of ≥99.0% and has strict limits on impurities such as chlorides, heavy metals, and iron.
Pharmaceutical Grade (USP/EP/BP): This is the highest purity grade of sodium sulfate. It must meet the rigorous standards of pharmacopoeias like the United States Pharmacopeia (USP), European Pharmacopoeia (EP), and British Pharmacopoeia (BP). This grade is used in pharmaceuticals, where it is critical that the product is free from contaminants.
Uses: As a laxative (Glauber’s salt), as a diluent or filler in tablet formulations, and in various pharmaceutical manufacturing processes.
Food Grade (FCC): Food-grade sodium sulfate is certified by organizations like the Food Chemicals Codex (FCC) and is safe for use in food products. It is used as a food additive, typically as a carrier or diluent for food colorants.
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