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What it is. This phosphoric acid is a 5% (w/w) aqueous solution supplied in a 55 gallon drum. It is a clear, colorless, dilute acid for production-scale cleaning, rust removal, metal pretreatment, and pH adjustment.
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What 5% (w/w) means. Every 100 g of solution contains 5 g of phosphoric acid. That equals roughly 0.5 M (calculated), a mild working strength that is effective for many cleaning and pH control tasks while far less hazardous to handle than 85% concentrate.
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Chemical identity. Phosphoric acid (orthophosphoric acid, CAS 7664-38-2, H3PO4, 98.00 g/mol) is a triprotic mineral acid with pKa values of about 2.15, 7.20, and 12.32. It is weaker than hydrochloric or sulfuric acid but reacts readily with metal oxides and carbonates.
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Rust removal and conversion. Phosphoric acid reacts with iron oxide to form iron phosphate, which dissolves rust and leaves a thin phosphate layer on steel. That layer improves paint adhesion and slows flash rusting, which is why phosphoric acid is a common metal pretreatment.
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Cleaning and descaling. Dilute phosphoric acid removes mineral scale, milkstone, and hard-water deposits from equipment and surfaces. It is widely used in food, dairy, and beverage plants for acid cleaning cycles, alongside alkaline washes.
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pH adjustment. Because it is a moderate, non-oxidizing acid, phosphoric acid is used to lower pH in water treatment, process streams, and formulations, and its phosphate salts provide buffering in the neutral range.
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Food and beverage use. Phosphoric acid is also a common food acidulant, best known for giving cola beverages their tartness, and dilute solutions are used for acid rinses in food processing. Confirm grade suitability before any food-contact use.
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Drum size for production. The 55 gallon drum supplies production lines, cleaning-in-place systems, and treatment operations that use dilute acid continuously, providing one consistent lot and reducing handling of concentrated acid. Use drum pumps rated for acids for dispensing.
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Handling at a glance. Five-percent phosphoric acid can irritate skin and eyes. Wear safety glasses or goggles and acid-resistant gloves, and rinse splashes with water. For concentrated acid, see Lab Pro's Phosphoric Acid 85%, ACS Grade (100 mL, 1 Pint).
Technical Specifications
| Chemical Name |
Phosphoric acid, aqueous solution |
| CAS Numbers |
7664-38-2 (phosphoric acid); 7732-18-5 (water) |
| EC Number (H3PO4) |
231-633-2 |
| Synonyms |
Orthophosphoric acid, dilute phosphoric acid |
| Formula (active) |
H3PO4 |
| Molecular Weight (active) |
98.00 g/mol |
| Concentration |
5% (w/w) |
| Approximate Molarity |
About 0.5 M (calculated) |
| pKa Values |
About 2.15, 7.20, 12.32 |
| Appearance |
Clear, colorless liquid |
| Physical State |
Liquid, aqueous solution |
| Hazard Profile |
Skin and eye irritant at this strength (confirm on SDS) |
| DOT |
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| Exposure Limits (phosphoric acid mist) |
OSHA PEL 1 mg/m³ TWA; NIOSH REL 1 mg/m³ TWA, 3 mg/m³ STEL |
| Package Size |
55 gallon drum |
Applications / Common Uses
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Rust removal: Converts and removes iron oxide from steel.
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Metal pretreatment: Leaves a phosphate layer that improves paint adhesion.
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Acid cleaning: Removes scale and milkstone in food and dairy plants.
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pH adjustment: Lowers pH in water treatment and process streams.
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Descaling: Dissolves hard-water deposits from equipment.
Storage, Handling & Shipping
Store the drum tightly closed in a cool, well-ventilated area on secondary containment, away from bases, reactive metals, and oxidizers. Use acid-rated drum pumps for dispensing and keep the area clean and clearly labeled.
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Incompatible materials: Strong bases, reactive metals (which release hydrogen), and strong oxidizers.
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Exposure limits (phosphoric acid mist): OSHA PEL 1 mg/m³ TWA; NIOSH REL 1 mg/m³ TWA, 3 mg/m³ STEL.
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Spill response: Contain, neutralize with sodium bicarbonate or lime, and rinse with water.
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First aid: Eyes or skin: rinse with water for several minutes and seek medical advice if irritation persists.
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GHS signal word: .
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DOT / shipping: .
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