What is the difference between a P2O5 and an H3PO4 percentage?

Two ways of stating the same phosphorus. The fertiliser trade expresses phosphorus as the oxide, P2O5; the chemical trade quotes the acid itself, H3PO4. To convert, multiply the H3PO4 percentage by 0.724. So 85% phosphoric acid is about 61.6% P2O5, and merchant-grade acid at 54% P2O5 is about 74.6% H3PO4. The gap is more than a quarter, so always state the basis in the contract.

What is the difference between wet-process and thermal phosphoric acid?

How it was made, which decides what else is in it. Wet-process acid comes from dissolving phosphate rock in sulfuric acid; it is cheap and made in huge volume, but carries fluorine, iron, aluminium, magnesium and heavy metals, and it is dark. It suits fertiliser. Thermal acid comes from burning elemental phosphorus and absorbing the oxide in water, which gives very pure acid at a high energy cost. Most food and technical acid today is purified wet acid, cleaned up by solvent extraction, with thermal acid kept for the most demanding uses.

Why has my 85% phosphoric acid turned solid?

Because it crystallises near 21 °C. It also supercools readily, so it can stay liquid well below that and then set suddenly when disturbed. The acid is not spoiled: warm it gently and it melts back. For unheated storage in a cold climate, 75% acid, which freezes near −17.5 °C, avoids the problem entirely.

What should phosphoric acid be stored in?

Purified acid at ambient temperature is well handled by 316L stainless steel, polyethylene, polypropylene or FRP. Wet-process acid is harsher than its strength suggests, because its fluoride and chloride attack stainless, so it needs higher alloys such as 904L or alloy 20, or rubber-lined steel. Carbon steel, aluminium, zinc and copper alloys are all unsuitable.

Does fertiliser-grade phosphoric acid contain cadmium?

It can. Cadmium occurs naturally in phosphate rock, in amounts that depend heavily on where the rock was mined, and wet-process acid carries it through. In the EU, the Fertilising Products Regulation (EU) 2019/1009 caps cadmium in phosphate fertilisers at 60 mg per kg of P2O5, and allows a low-cadmium claim at 20 mg per kg or below. If the acid is destined for EU fertiliser, ask for the cadmium figure on the certificate of analysis.

Why is phosphoric acid used in cola?

It gives a sharp, clean tartness at very low cost and lowers the pH, which also helps keep the drink stable. In the EU it is listed as food additive E338. Food use calls for food grade meeting Food Chemicals Codex test requirements, where the limits that matter are arsenic, heavy metals and fluoride rather than the assay.

Phosphoric Acid

CAS 7664-38-2 H₃PO₄

CAS number: 7664-38-2
EC number: 231-633-2
Formula: H₃PO₄
Molar mass: 98.00 g/mol
HS code: 2809.20

Supply of Phosphoric Acid

Grades: Traded as two very different families. Fertiliser or merchant-grade wet-process acid is quoted by its P2O5 content, typically 52–54% P2O5, and carries fluorine, iron, aluminium and heavy metals from the rock. Purified and thermal acids are quoted as H3PO4 at 75%, 80% and 85%, in technical grade, food grade meeting Food Chemicals Codex test requirements (E338), pharmaceutical and low-metal electronic grades. Specify the basis, strength and grade: a percentage without its basis is ambiguous by more than a quarter.
Packaging: 35 kg jerricans · Drums (~330 kg net), IBC · Stainless or rubber-lined ISO tanks and road tankers · Bulk vessels for merchant-grade acid
Documents: CoA, SDS and TDS on request; certificate of origin where the destination requires it.
Delivery: Worldwide, including the United States, Canada, the United Kingdom, Germany and the rest of the EU, the United Arab Emirates, India, Singapore, Malaysia and Australia. Quoted EXW, FOB, CIF or DAP.

Phosphoric acid is a mild mineral acid. Most of it goes into phosphate fertilizers, while purified grades give cola its tartness, clean dairy and food equipment, prepare metal surfaces for painting and are used in electronics manufacturing. Fertilizer grades are sold by phosphate content, purified grades at 75–85% strength.

Technical details

Safety & handling

Phosphoric acid is corrosive to skin and eyes, but it behaves more gently than the other mineral acids: it is not an oxidiser, it does not char organic matter the way concentrated sulfuric acid does, and it gives off no fumes at room temperature. That relative mildness is a reason for care rather than complacency, because concentrated acid still causes serious burns and hot acid more so. It attacks carbon steel and most common metals, releasing flammable hydrogen. Purified acid is handled in 316L stainless, polyethylene, polypropylene or FRP; wet-process acid, with its fluoride and chloride, calls for higher alloys such as 904L or alloy 20, or rubber-lined steel. Mixing it with strong alkalis releases a great deal of heat. The 85% grade starts to crystallise near 21 °C and the 80% grade near 5 °C, so cold storage needs heat tracing or a weaker strength. Follow the Safety Data Sheet (SDS).

Phosphoric acid is traded as two distinct products. Most of it is wet-process acid, made by dissolving phosphate rock in sulfuric acid, filtering off the gypsum and concentrating what is left into a dark, impure merchant grade that goes almost entirely into fertiliser. The rest is purified, either by solvent extraction of that wet acid or by burning elemental phosphorus, into the clear acid found in cola, dairy cleaners, metal treatment and electronics. The two are priced, specified and even measured differently: fertiliser acid by its P2O5 content, purified acid by its H3PO4 strength. The basis has to be stated on every enquiry, because 54% means something quite different in each. Among the mineral acids it is the mildest to handle, with no oxidising power and no fumes, though its 85% grade freezes near 21 °C. Ehlinar supplies merchant-grade and purified acid, in technical, food and high-purity grades.

Appearance: At the usual commercial strengths, a clear, colourless, odourless and syrupy liquid, markedly denser than water: about 1.69 g/mL at 85%. Pure 100% acid is a white crystalline solid melting near 42 °C. The 85% grade itself begins to crystallise near 21 °C. Merchant-grade fertiliser acid is dark green to black from the phosphate rock it was made from.

Applications

FertiliserMAP, DAP, TSP and liquid fertilisers, which take the large majority of world output

Food & beverageAcidulant in cola drinks (E338), pH control and food phosphate salts

Metal finishingPhosphate conversion coatings before painting, rust removal and electropolishing

Animal feedDicalcium and monocalcium phosphate feed supplements

CleaningDairy and brewery acid cleaners that remove milkstone and beerstone

ElectronicsHot-acid etching of silicon nitride and aluminium on high-purity grades

Water treatmentPhosphate corrosion inhibitors and pH adjustment

Dental & pharmaEnamel etching gels and pharmaceutical buffers

How we supply

Supplier documentation on request

Certificate of Analysis (CoA), lot-specific where available
Safety Data Sheet (SDS / MSDS)
Technical Data Sheet (TDS)
Certificate of Origin / Certificate of Conformity

Quality assurance

Independent third-party inspection can be arranged on request, with the agency and scope agreed per trade. Representative samples can be requested for qualification, subject to supplier availability. We recommend incoming quality control against the agreed CoA.

Delivery & terms

Quoted on standard Incoterms (e.g. EXW, FOB, CIF, DAP) as agreed per trade. Delivery region, packaging and grade are confirmed per quote.

Documents and services above are subject to supplier availability and confirmed per quote; nothing here is an offer.

Typical / indicative values — not a binding specification

Property	Typical
Commercial strengths	75%, 80%, 85% H3PO4; merchant grade 52–54% P2O5
P2O5 equivalent	%P2O5 = %H3PO4 × 0.724
Density at 25 °C (85%)	~1.685 g/mL
Crystallisation onset	~21 °C at 85%; ~5 °C at 80%; ~−17.5 °C at 75%
Transport	UN 1805, Class 8
Materials of construction	316L, PE, PP or FRP for purified acid; 904L, alloy 20 or rubber-lined steel for wet-process acid

Also known as

Orthophosphoric acid · o-Phosphoric acid · Phosphoric(V) acid · E338 · Wet-process acid (WPA) · Merchant-grade acid (MGA)

Frequently asked questions

What is the difference between a P2O5 and an H3PO4 percentage?: Two ways of stating the same phosphorus. The fertiliser trade expresses phosphorus as the oxide, P2O5; the chemical trade quotes the acid itself, H3PO4. To convert, multiply the H3PO4 percentage by 0.724. So 85% phosphoric acid is about 61.6% P2O5, and merchant-grade acid at 54% P2O5 is about 74.6% H3PO4. The gap is more than a quarter, so always state the basis in the contract.
What is the difference between wet-process and thermal phosphoric acid?: How it was made, which decides what else is in it. Wet-process acid comes from dissolving phosphate rock in sulfuric acid; it is cheap and made in huge volume, but carries fluorine, iron, aluminium, magnesium and heavy metals, and it is dark. It suits fertiliser. Thermal acid comes from burning elemental phosphorus and absorbing the oxide in water, which gives very pure acid at a high energy cost. Most food and technical acid today is purified wet acid, cleaned up by solvent extraction, with thermal acid kept for the most demanding uses.
Why has my 85% phosphoric acid turned solid?: Because it crystallises near 21 °C. It also supercools readily, so it can stay liquid well below that and then set suddenly when disturbed. The acid is not spoiled: warm it gently and it melts back. For unheated storage in a cold climate, 75% acid, which freezes near −17.5 °C, avoids the problem entirely.
What should phosphoric acid be stored in?: Purified acid at ambient temperature is well handled by 316L stainless steel, polyethylene, polypropylene or FRP. Wet-process acid is harsher than its strength suggests, because its fluoride and chloride attack stainless, so it needs higher alloys such as 904L or alloy 20, or rubber-lined steel. Carbon steel, aluminium, zinc and copper alloys are all unsuitable.
Does fertiliser-grade phosphoric acid contain cadmium?: It can. Cadmium occurs naturally in phosphate rock, in amounts that depend heavily on where the rock was mined, and wet-process acid carries it through. In the EU, the Fertilising Products Regulation (EU) 2019/1009 caps cadmium in phosphate fertilisers at 60 mg per kg of P2O5, and allows a low-cadmium claim at 20 mg per kg or below. If the acid is destined for EU fertiliser, ask for the cadmium figure on the certificate of analysis.
Why is phosphoric acid used in cola?: It gives a sharp, clean tartness at very low cost and lowers the pH, which also helps keep the drink stable. In the EU it is listed as food additive E338. Food use calls for food grade meeting Food Chemicals Codex test requirements, where the limits that matter are arsenic, heavy metals and fluoride rather than the assay.

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