Description
Phosphoric acid, with the chemical formula H3PO4, is a colorless, odorless inorganic compound that is a key industrial chemical. The “85%” designation refers to its common form as an 85% aqueous solution, a non-volatile, syrupy liquid. This concentration is a standard due to its high purity and the fact that a higher concentration can lead to the entire mass freezing solid, which is a major issue for large-scale storage and use.
Chemical Properties
| Property | Description |
| Appearance | Colorless, viscous liquid |
| Odor | Odorless |
| Density | ~1.685 g/cm³ at 25 °C |
| Boiling point | ~158 °C (concentrated solution may decompose) |
| Melting point | ~21 °C (for 85% solution) |
| Solubility in water | Completely miscible |
| pH | Strongly acidic (≈1 for 85% solution) |
| Viscosity | High, syrupy |
| Corrosiveness | Corrosive to metals and tissue |
| Volatility | Low |
Uses
Fertilizer Production: This is the most significant use of phosphoric acid, accounting for the vast majority of global production. It is used to manufacture phosphate-based fertilizers such as triple superphosphate (TSP) and diammonium phosphate (DAP), which supply the essential nutrient phosphorus to plants.
Food and Beverage Industry: A high-purity, food-grade version of phosphoric acid is used as a food additive (E338). Its functions include:
Acidulant: It provides a sharp, tangy flavor to soft drinks like cola.
Preservative: It helps to inhibit the growth of mold and bacteria, extending the shelf life of food products.
pH regulator: It is used to control the acidity in various processed foods, including jams, jellies, and cheese.
Metal Treatment: Phosphoric acid is highly effective in metalworking applications:
Rust Removal: When applied to rusted iron or steel, it reacts with iron oxide (rust) to form a protective layer of iron phosphate, a black, water-resistant compound that can be easily removed.
Metal Polishing and Etching: It’s used in the polishing of metals and in etching processes to prepare surfaces for painting or other coatings.
Other Industrial and Commercial Uses:
Detergents and Cleaners: It is a component in some heavy-duty cleaners and detergents.
Water Treatment: It is used to control pH and prevent scaling in water systems.
Dental and Pharmaceutical: It is used as an etching solution in dentistry and as an ingredient in some anti-nausea medications.
Catalyst: It can serve as a catalyst in various chemical processes, such as the production of certain organic compound
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