Phosphorous acid Application

Maybe everyone of us have heard of the compounds of Phosphorous acid,It also has widely application in many spects,Next let’s learn some application of it.


1.Rust removal

Phosphoric acid(CAS.NO:13598-36-2) may be used by direct application to rusted iron, steel tools or surfaces to convert iron(III) oxide (rust) to a water soluble phosphate compound. It is usually available as a greenish liquid, suitable for dipping (acid bath), but is more generally used as a component in a gel, commonly called Naval jelly. As a thick gel, it may be applied to sloping, vertical, or even overhead surfaces. Care must be taken to avoid acid burns of the skin and especially the eyes, but the residue is easily diluted with water. When sufficiently diluted it can even be nutritious to plant life, containing the essential nutrients phosphorus and iron. It is sometimes sold under other names, such as "rust remover" or "rust killer." It should not be directly introduced into surface water such as creeks or into drains, however. After treatment, the reddish-brown iron oxide will be converted to a black iron phosphate compound coating that may be scrubbed off. Multiple applications of phosphoric acid may be required to remove all rust. The resultant black compound can provide further corrosion resistance (such protection is somewhat provided by the superficially similar Parkerizing and blued electrochemical conversion coating processes.) After application and removal of rust using phosphoric acid compounds, the metal should be oiled (if to be used bare, as in a tool) or appropriately painted, most durably by using a multiple coat process of primer, intermediate, and finish coats.

2.Processed food use

It is also used to acidify foods and beverages such as various colas, but not without controversy as to its health effects. It provides a tangy taste, and being a mass-produced chemical, is available cheaply and in large quantities. The low cost and bulk availability is unlike more expensive natural seasonings that give comparable flavors, such as ginger for tangyness, or citric acid for sourness, obtainable from lemons and limes. (However most citric acid in the food industry is not extracted from citrus fruit, but fermented by Aspergillus niger mold from scrap molasses, waste starch hydrolysates and phosphoric acid.) It is labeled as E number E338.

3.Medical use

Phosphoric acid is used in dentistry and orthodontics as an etching solution, to clean and roughen the surfaces of teeth where dental appliances or fillings will be placed. Phosphoric acid is also an ingredient in over the counter anti-nausea medications which also contain high levels of sugar (glucose and fructose). It should not be used by diabetics without consultation with a doctor. Phosphoric acid is also used as a catalyst in the synthesis of aspirin because it provides a larger number of hydrogen ions with less contamination when compared to hydrochloric acid and sulfuric acid.Preparation of hydrogen halides
Phosphoric acid reacts with halides to form the corresponding hydrogen halide gas
(steamy fumes are observed on warming the reaction mixture).

4.Other applications

1)Orthophosphoric acid is used as the electrolyte in phosphoric-acid fuel cells.

2)It is used as an external standard for phosphorus-31 NMR.

3)It is used as a cleaner by construction trades to remove mineral deposits, cementitious smears, and hard water stains. It is also used as an ingredient in some household cleaners aimed at similar cleaning tasks.

4)Hot phosphoric acid is used in microfabrication to etch silicon nitride (Si3N4). It is highly selective in etching Si3N4 instead of SiO2, silicon dioxide.

5)Phosphoric acid is used as a flux by hobbyists (such as model railroaders) as an aid to soldering.

6)Phosphoric acid is also used in hydroponics 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. General Hydroponics pH Down liquid solution contains phosphoric acid in addition to citric acid and ammonium bisulfate with buffers to maintain a stable pH in the nutrient reservoir.

7)Phosphoric acid is used as a pH adjuster in cosmetics and skin care products.


8)Phosphoric acid is used as an chemical oxidizing agent for activated carbon production.