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What it is. This phosphoric acid is the concentrated 85% ACS reagent grade, offered in 100 mL and 1 pint sizes. It is a clear, colorless, syrupy liquid used for preparing buffers and standards, sample digestion, etching, and analytical chemistry.
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What ACS grade guarantees. ACS reagent phosphoric acid assays at 85.0% minimum and limits impurities such as chloride, nitrate, sulfate, volatile acids, iron, and heavy metals to low parts-per-million levels, with color no darker than 10 Hazen. Those limits make it suitable for analytical and buffer work.
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How concentrated it is. With a density of about 1.685 g/mL, 85% phosphoric acid contains roughly 1,430 g of H3PO4 per liter, about 14.6 M (calculated). It is viscous, mixes completely with water, and boils near 158 °C.
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A triprotic acid. Phosphoric acid releases three protons in steps, with pKa values of about 2.15, 7.20, and 12.32. That makes it the basis of phosphate buffers across a wide range, including the widely used pH 7 region of dihydrogen and hydrogen phosphate.
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Freezing behavior. Concentrated phosphoric acid can crystallize at cool temperatures, since the pure 85% solution has a melting point near 21 °C. If crystals form, warm it gently to room temperature and mix before use.
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Laboratory uses. Labs use 85% phosphoric acid to prepare phosphate buffers and HPLC mobile phases, acidify samples, digest and dissolve materials, catalyze reactions such as dehydrations, and as an etchant in semiconductor processing for silicon nitride at elevated temperature.
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Diluting safely. To prepare dilute phosphoric acid, add the concentrated acid slowly to water with stirring. Dilution releases heat, though less violently than with sulfuric acid. Because the 85% acid is viscous, rinse measuring glassware carefully to transfer the full volume.
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Two sizes. The 100 mL size (ZP0995-125) suits occasional buffer preparation and teaching labs, while the 1 pint size (ZP0995-16) supports labs that prepare buffers and mobile phases regularly.
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Handling at a glance. Concentrated phosphoric acid causes severe skin burns and eye damage and is corrosive to metals. Wear chemical splash goggles and acid-resistant gloves, and add acid to water when diluting. For dilute acid in bulk, see Lab Pro's Phosphoric Acid 5% (w/w), 55 Gallon Drum.
Technical Specifications
| Chemical Name |
Orthophosphoric acid, aqueous solution |
| CAS Numbers |
7664-38-2 (phosphoric acid); 7732-18-5 (water) |
| EC Number |
231-633-2 |
| Synonyms |
Phosphoric acid, orthophosphoric acid, o-phosphoric acid |
| Formula |
H3PO4 |
| Molecular Weight |
98.00 g/mol |
| Grade |
ACS reagent |
| Assay |
85.0% min |
| Color |
10 Hazen max |
| Chloride (Cl) |
2 ppm max |
| Nitrate (NO3) |
3 ppm max |
| Sulfate (SO4) |
20 ppm max |
| Volatile Acids (as acetic acid) |
10 ppm max |
| Iron (Fe) |
10 ppm max |
| Heavy Metals (as Pb) |
10 ppm max |
| Insoluble Matter |
10 ppm max |
| Density |
About 1.685 g/mL (25 °C) |
| Approximate Molarity |
About 14.6 M (calculated) |
| pKa Values |
About 2.15, 7.20, 12.32 |
| Boiling Point |
About 158 °C |
| Melting Point |
About 21 °C |
| Hazard Statements |
H290 (corrosive to metals), H314 (severe burns) |
| DOT |
UN1805, Phosphoric acid solution, Class 8, PG III |
| Exposure Limits |
OSHA PEL 1 mg/m³ TWA; NIOSH REL 1 mg/m³ TWA, 3 mg/m³ STEL |
| Package Sizes |
100 mL; 1 pint |
Available Variants
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ZP0995-125: 100 mL for occasional buffer preparation and teaching labs.
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ZP0995-16: 1 pint for regular buffer and mobile-phase preparation.
Applications / Common Uses
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Phosphate buffers: Prepares buffers across pH 2 to 12.
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HPLC mobile phases: Acidifies and buffers mobile phases.
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Sample digestion: Dissolves and acidifies samples.
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Catalysis: Catalyzes dehydration and other acid reactions.
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Nitride etching: Etches silicon nitride at elevated temperature.
Storage, Handling & Shipping
Caution: 85% phosphoric acid causes severe skin burns and eye damage and is corrosive to metals. Wear chemical splash goggles and acid-resistant gloves, and always add acid to water when diluting.
Store tightly closed at room temperature in a corrosives cabinet, away from bases, reactive metals, and oxidizers. Avoid cold storage, which can cause the concentrated acid to crystallize; if crystals form, warm gently and mix before use.
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Incompatible materials: Strong bases, reactive metals (which release hydrogen), and strong oxidizers.
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Exposure limits: 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, and rinse with water.
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First aid: Skin or eyes: flush with water for at least 15 minutes and seek medical attention.
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GHS signal word: Danger.
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DOT / shipping: UN1805, Phosphoric acid solution, Class 8, PG III.
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