Monday 22 December 2014

PHOSPHORIC ACID

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. Orthophosphoric acid refers to phosphoric acid, which is the IUPAC name for this compound. The prefix ortho is used to distinguish the acid from related phosphoric acids, called polyphosphoric acids. Orthophosphoric acid is a non-toxic acid, which, when pure, is a solid at room temperature and pressure.

The conjugate base of phosphoric acid is the dihydrogen phosphate ion, H2PO−4, which in turn has a conjugate base of hydrogen phosphate, HPO2−4, which has a conjugate base of phosphate, PO3−4.

In addition to being a chemical reagent, phosphoric acid has a wide variety of uses, including as a rust inhibitor, food additive, dental and orthop(a)edic etchant, electrolyte, flux, dispersing agent, industrial etchant, fertilizer feedstock, and component of home cleaning products.

The most common source of phosphoric acid is an 85% aqueous solution; such solutions are colourless, odourless, and non-volatile. The 85% solution is a rather viscous, syrupy liquid, but still pourable. Because it is a concentrated acid, an 85% solution can be corrosive, although nontoxic when diluted. Because of the high percentage of phosphoric acid in this reagent, at least some of the orthophosphoric acid is condensed into polyphosphoric acids. For the sake of labeling and simplicity, the 85% represents H3PO4 as if it were all orthophosphoric acid. Dilute aqueous solutions of phosphoric acid exist in the ortho- form.

Phosphoric acid is used:

> As an external standard for phosphorus-31 Nuclear magnetic resonance (NMR).
> As a buffer agent in biology and chemistry; For example, a buffer for high-performance liquid chromatography.
> As a chemical oxidizing agent for activated carbon production, as used in the Wentworth Process.[12]
> As the electrolyte in phosphoric acid fuel cells. With distilled water (2–3 drops per gallon) as an electrolyte in oxyhydrogen
generators.
> As a catalyst in the hydration of alkenes to produce alcohols, predominantly ethanol.
> As an electrolyte in copper electropolishing for burr removal and circuit board planarization.
> As a flux by hobbyists (such as model railroaders) as an aid to soldering.
In compound semiconductor processing, phosphoric acid is a common wet etching agent: for example, in combination with hydrogen
peroxide and water it is used to etch InGaAs selective to InP.[13]
Heated in microfabrication to etch silicon nitride (Si3N4). It is highly selective in etching Si3N4 instead of SiO2, silicon
dioxide.[14]
> As a cleaner by construction trades to remove mineral deposits, cementitious smears, and hard water stains.
> As a chelant in some household cleaners aimed at similar cleaning tasks.
In hydroponics pH solutions to lower the pH of nutrient solutions. While other types of acids can be used, phosphorus is a nutrient
used by plants, especially during flowering, making phosphoric acid particularly desirable.
> As a pH adjuster in cosmetics and skin-care products.[15]
> As a dispersing agent in detergents and leather treatment.
> As an additive to stabilize acidic aqueous solutions within a wanted and specified pH range.

Source : http://en.wikipedia.org/wiki/Phosphoric_acid

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