Phosphoric acid & Phosphorous acid

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Phosphoric acid

Phosphoric acid (also known as orthophosphoric acid or phosphoric acid) is a weak acid with the chemical formula H3PO4.

Phosphorus is an essential plant nutrient and is taken up by plant roots, usually as the dihydrogenphosphate ion, H2PO4-, derived from phosphoric acid, H3PO4. The manufacture of fertilizers that are used to rectify phosphorus deficiencies in soils depends on the availability of supplies of phosphoric acid.

Manufacture process of phosphoric acid is made by two processes: 1 the 'wet' process 2 thermal process The thermal method normally produces a more concentrated and purer product, but is energy intensive because of the manufacture of phosphorus itself. Acid produced by the 'wet' route is less pure but is used in the manufacture of fertilizers.

Many specific applications of phosphoric acid include:

In anti-rust treatment by phosphate conversion coating

As an external standard for phosphorus-31 nuclear magnetic resonance.

In phosphoric acid fuel cells.

In activated carbon production.

In compound semiconductor processing, to etch Indium gallium arsenide selectively with respect to indium phosphide.

In microfabrication to etch silicon nitride selectively with respect to silicon dioxide.

As a pH adjuster in cosmetics and skin-care products.

As a sanitizing agent in the dairy, food, and brewing industries.

Phosphorous acid

Phosphorous acid is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds.

The most important use of phosphorous acid (phosphonic acid) is the production of basic lead phosphite, which is a stabilizer in PVC and related chlorinated polymers.

Phosphites have shown effectiveness in controlling a variety of plant diseases, in particular, treatment using either trunk injection or foliar containing phosphorous acid salts is indicated in response to infections by phytophthora and pythium-type plant pathogens such as dieback/root rot and downy mildew. Anti-microbial products containing salts of phosphorous acid are marketed in Australia as 'Yates Anti-Rot'; and in the United States of America, for example, aluminum salts of the monoethyl ester of phosphorous acid are sold under the trade name 'Aliette' and potassium salts of phosphorous acid are sold under the trade name ProPhyt. Phosphorous acid and its salts, unlike phosphoric acid, are somewhat toxic and should be handled carefully. 

erik@nbschem.com