Phosphoric Acid


Phosphoric acid is a mineral inorganic acid made up of phosphorous, oxygen and hydrogen. Phosphoric acid is an essential part of the body of organisms, as the constituent of bones and teeth, as well as in many metabolic proceses of carbohydrate, fat and protein. Phosphoric acid is abundantly available in natural foods in the form of free phosphoric acid itself, or as the mineral salts.

General properties of Sulphuric acid

  • Phosphoric acid is a clear, colorless, nontoxic odorless liquid with a viscous consistency.
  • Phosphoric acid is a medium strong acid and attacks metals to release flammable hydrogen gas.
  • Phosphoric acid is a strong oxidizing agent.


Production of Phosphoric acid

Phosphoric acid is made industrially by two general routes such as thermal process and wet process.

  • Wet process
  • Wet process is a commercially dominative process for a commercial production of phosphoric acid. Phosphoric acid is prepared by adding sulphuric acid to tricalcium phosphate rock.
    Ca5(PO4)3X + 5 H2SO4 + 10 H2O → 3 H3PO4 + 5 CaSO4•2 H2O + HX
    The initial phosphoric acid contains 22 – 23 % of P2O5, but can be concentrated by the evaporation of water to produce a commercial grade phosphoric acid, which contains about 54% P2O5. Digestion of the phosphate ore using sulfuric acid yields the insoluble calcium sulfate (gypsum), which is filtered and removed as phosphogypsum.

  • Thermal method
  • Very pure phosphoric acid is obtained by burning elemental phosphorus mineral to produce phosphorus pentoxide, which is subsequently dissolved in dilute phosphoric acid. This process produces a very pure phosphoric acid and most of the impurities present in the rock have been removed when extracting phosphorus from the rock in a furnace. The end result is food-graded thermal phosphoric acid.

  • Laboratory sunthesis
  • High grade phosphoric acid is obtained by the oxidation of red Phosphorous with nitric acid
    P + 5 HNO3 → H2O + H3PO4 + 5 NO2

  • Fertilizer Industry
  • Phosphoric acid and its phosphate derivatives are used for the production of water soluble and liquid fertilizers. Phosphorus is an essential plant nutrient and is taken up by plant roots as the dihydrogenphosphate ion, H2PO4, derived from phosphoric acid, H3PO4.

  • Detergent Industry
  • Phosphoric acid is used in the production of acid based detergent. Acid detergents are used in a two-step sequential cleaning regime with alkaline detergents. Phosphoric acid is prevention or removal of beerstone, water scale (calcium and magnesium carbonates), and aluminium oxide. Acid detergents is more affective against bacteria then alkaline detergents.

  • Food Industry
  • In the food industry, phosphoric acid is used to acidify foods and beverages. Various salts of phosphoric acid are used as a leavening agent.Phosphoric acid provide tangy or sour taste to the processed food like various colas.

  • Water treatment
  • Phosphoric acid is applied to take away unwanted metal salts from the barren water in water treatment industry. Phosphoric acid is used to convert hard water to soft water by removing the metal ions. Phosphoric acid is extensively used to reduce the risk of preventing the deposit of limescale and control the pH of water.

  • Pharmaceutical industry
  • In the medical applications, Phosphoric acid is extensively applied in dentistry and orthodontics as an etching solution. Phosphoric acid is also an integral component in anti-nausea medication issues because it contains high levels of sugar. Phosphoric acid is likewise practiced in many teeth bleaching agents to eliminate plaque problems. In dental application, phosphoric acid is mixed with the zinc phosphate as a temporary dental cement for patients.

  • Other aplications>
  • In the semiconductor industry, phosphoric acid is used as a common etching agent in microfabrication process. Phosphoric acid is utilized in the electrical sheet industry in the production of magnetic grain-oriented electrical sheets and high quality low-loss transformers. Phosphoric acid is utilized as a surface cleaning rust removal agent for rusted iron, steel instruments, or other surfaces. Purified phosphoric acid is utilized in the aluminum industry, to purify vegetable oils and active carbon filters, to manufacture titanium oxide and in combination with sulphuric acid it is used in Electropolishing. It is also used as an excellent dispersants in the ceramic and enamel industries, paint and paper pulp manufacturing, and manufacture of fiberglass products. In flame retardants, phosphoric acid is used for the fireproofing material and it’s one of the ingredients in fire-extinguisher products. Phosphoric acid exhibits excellent electrolyte properties and used in phosphoric acid fuel cells.


CAS NO. : 7664-38-2
Formula : H3PO4
Molar mass : 97.994 g/mol
Appearance : white solid or colorless, viscous liquid (>42 °C)
Density : 1.885 g/ml (liquid)
: 1.685 g/ml (85% solution)
: 2.030 g/ml (crystal at 25 °C)
Melting point : 42.35 °C
Boiling point : 158 °C (decomp)
Solubility in water : 5.48 g/ml
Acidity (pka) : 2.148, 7.198, 12.375
Viscosity : 2.4–9.4 cp (85% aq. soln.)
: 147 cp (100%)
Other Name : Orthophosphoric acid