Phosphoric acid
- Ortho- phosphoric acid
- Phosphorus (V ) acid
- E 338
Colorless and odorless solid or liquid
Fixed (often liquid, as a supercooled melt is quite long storable )
1.87 g · cm -3 ( 25 ° C)
42.35 ° C
Decomposition: 213 ° C ( dehydration )
3.8 Pa ( 20 ° C)
- PKS1: 2.16
- PKa2: 7.21
- PKS3: 12.32
Completely miscible with water
Risk
2 mg · m -3 ( inhalable aerosol fraction)
Template: Infobox chemical / molecular formula search available
The "normal" or ortho- phosphoric acid is the principal oxygen acid of phosphorus, and one of the most important inorganic acids. She is a triple proton acid and reacts with respect to the first deprotonation as a medium strong acid. Its salts and esters hot phosphates; also the name of organophosphates is common for esters of phosphoric acid. The phosphorus in these compounds has an oxidation state of V. Important work on the elucidation of the structure made Thomas Graham.
From the phosphoric acid is also derived from the condensates diphosphonic acid, meta- and polyphosphoric acids.
As a food additive phosphoric acid is declared as E 338.
Production and representation
Phosphoric acid can be produced and sulfuric acid, hydrochloric acid or nitric acid from rock phosphate ( apatite, Ca5 (PO4) 3X with X = F, OH or Cl mostly). Here are obtained as byproducts CaSO4 ( phosphogypsum, contaminated gypsum) and H2 [ SiF 6 ] to ( hexafluorosilicic ). Alternatively, phosphoric acid can be by burning elemental phosphorus to phosphorus pentoxide, P4O10, and subsequent hydrolysis to produce ( so-called thermal phosphoric acid). A highly pure product is obtained by concentrating a commercially available phosphoric acid solution to a level of about 90 percent and subsequent crystallization in a precisely maintained temperature range.
Properties
The anhydrous substance is very hygroscopic. Usually it comes as a 85 - % aqueous solution on the market.
The phosphoric acid is a triple proton acid that can give up their protons in three stages to water molecules to form hydronium ( H3O ) and the formation of dihydrogen phosphate, hydrogen phosphate or phosphate anions. The corresponding pK values are PKS1 = 2.161; pKa2 = 7.207 and PKS3 = 12,325.
Use
Phosphoric acids used as starting material for the production of phosphate fertilizer (in the U.S. > 90 % of production), detergents, rust removers or of rust converter and for the passivation of iron and zinc to protect against corrosion. In dental zinc phosphate cement is used.
Phosphoric acid is used for the preparation of buffer solutions ( see phosphate buffer).
Phosphoric acid is corrosive in high concentrations, diluted it is in the food industry as a preservative, acidulant (eg in cola drinks ), as an acidity regulator and ( to as an antioxidant to the rancidity of fats and discoloration of, for example meat, sausage or pie fillings prevent ) used ( e 338 ). Phosphoric acid is non-toxic to their corrosive effect on the human organism in healthy subjects.
Biological Significance
Phosphates and polyphosphates play a central role in metabolism, particularly as energy and group carriers ( see, eg, ATP or GTP). They include integral part of DNA, RNA, and many coenzymes.
In medicine, the fortification of food with acid (E 338 ) of specific medical conditions is contraindicated. Diseases such as chronic renal failure (even with dialysis treatment), osteoporosis and urolithiasis (calcium phosphate stones ) require a low-phosphate diet. ( s.a. Main article hyperphosphatemia )
Proof
The phosphoric acid and soluble phosphates can be detected by precipitation with ammonium heptamolybdate to MgNH4PO4 to yellow Ammoniummolybdatophosphat, or by precipitation with magnesium ions in ammoniacal solution.