Phosphoric acid, also known as orthophosphoric acid, is one of the most widely known and used acids. It is a mineral acid that contains three atoms of hydrogen, one atom of phosphorus, and four atoms of oxygen. Thus, the chemical formula of phosphoric acid is H3PO4. This is an important acid which has a wide range of uses. In the following sections, we will find out what all phosphoric acid is used for.

Removal of Rust
One of the most common uses of phosphoric acid is for the removal of rust from metal surfaces. It acts as a rust converter on direct application to rusted iron, steel, and other metal surfaces. It converts reddish-brown iron, that is, ferric oxide, to black-colored ferric phosphate. After this treatment, the black ferric phosphate coating can be easily scrubbed off, revealing the underlying fresh metal surface.

For complete rust removal, multiple applications of phosphoric acid may be needed. In some applications, where exterior appearance is secondary, the black phosphate coating formed on applying this acid may be left in place so that it provides further corrosion resistance. The phosphoric acid based rust remover is a greenish liquid that is suitable for dipping, but it is more often formulated as a gel for easy application.

Use in Processed Food
Phosphoric acid is used as an additive to acidify foods and beverages, like the various colas. It provides a tangy or sour taste, and as it is mass produced, this chemical is quite easily available.

This particular use of phosphoric acid, however, has stirred up a controversy, as many have raised questions regarding the health effects it may have on the human body.

Medical Uses
One of its important uses is in the fields of medicine and dentistry. Phosphoric acid is used as an ingredient in over-the-counter anti-nausea medications, which also happen to contain high levels of sugar, that is, glucose and fructose. In dentistry, this acid is combined with zinc powder to form zinc phosphate, which is used as a temporary dental cement. It is also used in orthodontics as an etching solution, so as to clean and roughen the surface of teeth before the placement of brackets and other dental appliances. This acid is also used in many teeth whitening solutions to eliminate plaque that may be present on the surface of the teeth.

Other Uses
It is used as an electrolyte in phosphoric acid fuel cells. It is also used as a cleaner in construction-related trades, so as to remove mineral deposits, cement smears, and hard water stains.

Hot phosphoric acid is used in micro-fabrication to etch silicon nitride. It is used as a flux by hobbyists to aid in the process of soldering. It is also used in hydroponics pH solutions to lower the pH of nutrient solutions.

Phosphoric acid is also used as an electrolyte in copper electro-polishing for burr removal. In compound semiconductor processing, it is a commonly used as a wet etching agent.

This acid is used as a pH adjuster in cosmetics and other skin care products. It is also used as a chemical oxidizing agent for activated carbon productions. It is used with distilled water as an electrolyte in oxyhydrogen generators.

Thus, phosphoric acid is an important acid which has several different applications in various industries, ranging from metallurgy to the food industry. It is one of the most important and useful chemicals known to man.