Phosphoric acid (also known as orthophosphoric acid or phosphoric(V) acid) is a mineral (inorganic) acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way. The term phosphoric acid can also refer to a chemical or reagent consisting of phosphoric acids, such as pyrophosphoric acid or triphosphoric acid, but usually orthophosphoric acid.
There are two distinct kinds of orthophosphoric acid, based on the method of preparation. They are known as thermal phosphoric acid and wet phosphoric acid.
Thermal phosphoric acid: This very pure phosphoric acid is obtained by burning elemental phosphorus to produce phosphorus pentoxide and dissolving the product in dilute phosphoric acid. This is the cleanest way of producing phosphoric acid, since most impurities present in the rock have been removed when extracting phosphorus from the rock in a furnace. The end result is food grade, thermal phosphoric acid; however, for critical applications additional processing to remove arsenic compounds may be needed.
Wet phosphoric acid: Green phosphoric acid is prepared by adding sulfuric acid to calcium phosphate rock, or slurry. The reaction for calcium phosphate slurry is:
3H2SO4(aq) + Ca3(PO4)2(aq) + 6H2O(l) ↔ 2H3PO4(aq) + 3CaSO4(aq)+ 6H2O(l)
Through modern filtering techniques the wet process acid can be cleaned up significantly but still isn’t as pure as thermal phosphoric acid; as it may contain other acidic species such as hydrofluoric acid.
CAS Registry Number:7664-38-2
Synonyms:Orthophosphoric acid; PA
Density:1.685 g/mL at 25℃ (lit.)
Storage Temperature:Store in a tightly closed container. Store in a cool, dry, well-ventilated area away from incompatible substances. Keep away from metals. Corrosives area. Do not store in metal containers.
Refractive index:n20/D 1.433
Stability:Stable at room temperature in closed containers under normal storage and handling conditions.
Chemical Properties:Clear liquid
Usage:Phosphorous acid is used for reaction with inorganic and organic products, for water treatment, industrial and agricultural uses. It is also used to bleach industrial and cleaning supplies.
General Description:A clear colorless liquid or transparent crystalline solid. The pure solid melts at 42.35°C and has a density of 1.834 g / cm3. Liquid is usually an 85% aqueous solution. Shipped as both a solid and liquid. Corrosive to metals and tissue. Used in making fertilizers and detergents and in food processing.
Air & Water Reactions: Soluble in water with small release of heat.
Reactivity Profile: Phosphorous acid reacts exothermically with bases. May react with active metals, including such structural metals as aluminum and iron, to release hydrogen, a flammable gas. Can initiate the polymerization of certain classes of organic compounds. Reacts with cyanide compounds to release gaseous hydrogen cyanide. May generate flammable and/or toxic gases in contact with dithiocarbamates, isocyanates, mercaptans, nitrides, nitriles, sulfides, and strong reducing agents. Forms explosive mixture with nitromethane. Reacts violently with sodium tetrahydroborate. In the presence of chlorides can corrode stainless steel to form explosive hydrogen gas. Emits toxic and irritating fumes of oxides of phosphorus when heated to decomposition.
Health Hazard: Burns on mouth and lips, sour acrid taste, severe gastrointestinal irritation, nausea, vomiting, bloody diarrhea, difficult swallowing, severe abdominal pains, thirst, acidemia, difficult breathing, convulsions, collapse, shock, death.
Fire Hazard: Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated.