- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 | |
| 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
- Rust removal: Converts and removes iron oxide from steel.
- Metal pretreatment: Leaves a phosphate layer that improves paint adhesion.
- Acid cleaning: Removes scale and milkstone in food and dairy plants.
- pH adjustment: Lowers pH in water treatment and process streams.
- 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.
- Incompatible materials: Strong bases, reactive metals (which release hydrogen), and strong oxidizers.
- Exposure limits (phosphoric acid mist): OSHA PEL 1 mg/m³ TWA; NIOSH REL 1 mg/m³ TWA, 3 mg/m³ STEL.
- Spill response: Contain, neutralize with sodium bicarbonate or lime, and rinse with water.
- First aid: Eyes or skin: rinse with water for several minutes and seek medical advice if irritation persists.
- GHS signal word: .
- DOT / shipping: .
Related Categories & Services
- Shop Acids for related products in this category.
- Explore Inorganic Chemicals and Buffers, Standards & Solutions.
- Vendor Managed Inventory (VMI) Program: Lab Pro can stock, track, and replenish this item on site so it never runs out. Contact info@labproinc.com or 888-452-2776 to set up a VMI assessment.
Related Articles
FAQs
What is 5% phosphoric acid used for?
It is used for rust removal and metal pretreatment, acid cleaning and descaling in food, dairy, and beverage plants, removing hard-water deposits, and adjusting pH in water treatment and process streams. Its mild strength suits continuous production use with less hazard than concentrated acid. It also leaves no oxidizing residue.
How does phosphoric acid remove rust?
Phosphoric acid reacts with iron oxide to form iron phosphate, dissolving rust and leaving a thin phosphate layer on the steel surface. That layer slows new rust formation and improves paint and coating adhesion, which is why phosphoric acid is a standard metal pretreatment. Rinse treated parts before coating.
Is 5% phosphoric acid hazardous?
At 5%, phosphoric acid is mainly a skin and eye irritant rather than a severe corrosive. Wear safety glasses or goggles and acid-resistant gloves, rinse splashes with water, and keep it away from bases and reactive metals. Confirm the exact classification on the safety data sheet.
How do I dispense from a 55 gallon drum safely?
Use a drum pump or dispensing tap rated for acids, keep the drum on secondary containment, and ground equipment where required. Wear goggles and gloves when connecting pumps, and label transfer containers clearly with the contents and concentration. Inspect pumps and fittings regularly for wear or leaks, since acid can degrade incompatible seals over time.
What is the difference between 5% and 85% phosphoric acid?
The 85% grade is concentrated acid, about 14.6 M, and causes severe burns. The 5% solution is about 0.5 M and is mainly an irritant. The dilute grade suits cleaning and pH adjustment, while 85% is used for preparing solutions and specialized chemistry. Choose by application.
Related Products
