The use of phosphoric acid in the home, agriculture and food industry – chemical properties

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Fans of the Coca-Cola carbonated drink are unlikely to look at its composition, which has the addition of E338. This substance is phosphoric acid, which is used not only in the food industry, but also in the textile, agricultural, and even copes with rust on the surface of parts. What are the properties of a chemical compound, what are its uses, what you need to know about safety measures – it is worth considering in more detail.

What is phosphoric acid?

At room temperature, these are hygroscopic colorless crystals of a rhomboid type that dissolve well with water. The phosphoric compound is considered an inorganic acid with medium strength. One of its forms, a yellowish or colorless syrupy liquid, odorless, is an aqueous solution with a concentration of 85%. Its other name is white phosphoric acid..

Chemical phosphoric compound has the following properties:

  • soluble in ethanol, water, solvents;
  • forms 3 rows of salts – phosphates;
  • causes burns on skin contact;
  • when interacting with metals forms a combustible, explosive hydrogen;
  • boiling temperature depends on the concentration – from 103 to 380 degrees;
  • the liquid form is prone to hypothermia;
  • incompatible with combustible materials, pure metals, quicklime, alcohol, calcium carbide, chlorates;
  • at a temperature of 42.35 degrees it melts, but does not decompose.

Soldering fluorophosphoric acid


Phosphoric acid is an inorganic compound that is described by the formula H3PO4. Its molar mass is 98 g / mol. The microparticle of the substance is built in space so that it connects the atoms of hydrogen and oxygen. The formula shows that a chemical substance has the following composition:


Number of atoms

Mass percentage










Production of phosphoric acid

A chemical compound has several production methods. A well-known industrial method for the manufacture of phosphoric acid is thermal, in which a pure high-quality product is obtained. The following process takes place:

  • oxidation during combustion with an excess of phosphorus air to phosphoric anhydride having the formula P4O10;
  • hydration, absorption of the resulting substance;
  • phosphoric acid condensation;
  • gaseous mist collection.

There are two other methods for the production of phosphoric compounds:

  • The extraction method, characterized by efficiency. Its basis is the decomposition of natural phosphate minerals with hydrochloric acid..
  • Under laboratory conditions, the substance is obtained by the interaction of white phosphorus, which is toxic with dilute nitric acid. The process requires strict safety precautions..

Chemical properties

An inorganic compound is considered to be tribasic, having medium strength. The following chemical properties of phosphoric acid are characteristic:

  • reacts to indicators by changing the color to red;
  • when heated, is converted to pyrophosphoric acid;
  • in aqueous solutions undergoes three-stage dissociation;
  • when reacting with strong acids, it forms phosphoryl – complex salts;
  • forms a yellow precipitate, interacting with silver nitrate;
  • thermally decomposes to diphosphoric acid;
  • in contact with bases, amorphous hydroxides, forms water and salt.

Phosphoric acid crystals in a plate


Phosphoric acid is used in many fields, ranging from industry to dentistry. The tool is used by craftsmen as a flux when soldering, to clean the surface of the metal from rust. Liquid is applied:

  • for scientific research in molecular biology;
  • as a catalyst for organic synthesis processes;
  • to create anti-corrosion coatings of metals;
  • in the manufacture of refractory impregnation for wood.

The substance is used in:

  • in the oil industry;
  • in the manufacture of matches;
  • for the production of film;
  • to protect against corrosion;
  • for clarification of sucrose;
  • in the manufacture of medicines;
  • in refrigeration units as a binder in the composition of freon;
  • during machining for polishing, metal cleaning;
  • in the textile industry in the manufacture of fabrics having flame retardant impregnation;
  • as a component in the preparation of chemicals;
  • in veterinary medicine for the treatment of urolithiasis in minks;
  • as a component for a primer for metal.

In the food industry

The widespread use of phosphoric acid in the manufacture of food products. It is registered in the register of food additives under the code E338. When used with acceptable amounts, the substance is considered safe. Useful are the following properties of the drug:

  • prevention of rancidity;
  • acidity regulation;
  • extension of shelf life;
  • preservation of taste characteristics;
  • increased antioxidant effects.

Orthophosphoric acid as an acidifier, baking powder, antioxidant is used in bakery, meat, dairy industry. Used in the manufacture of confectionery, sugar. The substance gives the product a sour, bitter taste. Additive E338 is part of:

  • processed cheeses;
  • muffins;
  • carbonated drinks – Pepsi-Cola, Sprite;
  • sausages;
  • bun;
  • milk;
  • baby food;
  • marmalade;
  • of cakes.

Cream cheese and knife

Studies have shown that the abuse of products containing phosphoric compounds, especially carbonated drinks, can lead to health problems. Not excluded:

  • leaching of calcium from the body, which can trigger the formation of osteoporosis;
  • violation of the acid-base balance – the additive is able to increase its acidity;
  • the appearance of gastrointestinal diseases;
  • exacerbation of gastritis;
  • destruction of tooth enamel;
  • caries development;
  • vomiting.

In the non-food industry

The use of phosphoric acid can be observed in many areas of production. Often this is due to the chemical properties of the product. The drug is used for the manufacture of:

  • combined phosphorus mineral fertilizers;
  • activated carbon;
  • phosphoric salts of sodium, ammonium, manganese;
  • fire retardant paints;
  • glass, ceramics;
  • synthetic detergents;
  • refractory binders;
  • non-combustible phosphate foam;
  • hydraulic fluids for the aviation industry.

In medicine

Dentists use an orthophosphoric composition to treat the inner surface of the crown. This helps during prosthetics to improve its adhesion to the tooth. The substance is used by pharmacists for the preparation of medicines, dental cement. In medicine, the use of an orthophosphoric compound is associated with the ability to etch tooth enamel. This is necessary when using adhesive materials of the second, third generation for sealing. Important points – after etching, the surface must:

  • Rinse;
  • to dry.


Rust application

A rust converter based on phosphoric acid creates a protective layer on the surface that protects against corrosion during future use. The peculiarity of the use of the compound is safety for metal during application. There are several ways to perform rust removal with phosphoric acid, depending on the size of the damage:

  • etching with immersion in a bath, another container;
  • repeated application of the composition to the metal with a spray gun, roller;
  • surface treatment by pretreated mechanical cleaning.

The phosphoric compound converts rust to iron phosphates. The composition can be used for washing and cleaning:

  • metal products;
  • wells;
  • pipeline surfaces;
  • steam generators;
  • water supply, heating systems;
  • coils;
  • boilers;
  • water heaters;
  • heat exchangers;
  • boilers;
  • machine parts and mechanisms.

Phosphoric Acid Reaction

The properties of an inorganic substance determine its interaction with other substances and compounds. In this case, chemical reactions occur. Phosphoric composition interacts with:

  • salts of weak acids;
  • hydroxides, entering into a neutralization reaction;
  • metals located to the left of hydrogen in a series of activities with the formation of salt and hydrogen evolution;
  • basic oxides participating in the exchange reaction;
  • ammonium hydroxide, creating ammonium hydrogen phosphate;
  • ammonia to obtain acid salts.

Chemicals in flasks

Acid Safety

Phosphoric compound belongs to the class of hazardous substances, requires caution. Work with the composition should be carried out in a special room equipped with supply and exhaust ventilation, away from sources of fire. Unacceptable lack of personal protective equipment:

  • respirator;
  • gloves;
  • special clothes;
  • non-slip boots;
  • points.

It is dangerous to get the phosphoric compound on the skin, in the eyes, inhalation of hot vapors is harmful. This can cause burns, dizziness, vomiting, and coughing. In case of emergency you need:

  • take off clothing that has been exposed to the substance;
  • rinse the affected area with running water;
  • call a doctor;
  • apply a loose dressing;
  • neutralize spilled liquid with alkali.

Transportation rules

There are special GOSTs that stipulate the rules for the transportation of phosphoric acid, which refers to dangerous goods. The substance can be delivered by any means of transport. Reactive liquid is transported in tightly closed:

  • steel tank trucks;
  • large bottles of polyethylene, glass;
  • plastic cubes;
  • barrels;
  • canisters;
  • gummed tank cars.

Steel tank truck


Orthophosphoric acid can be purchased in pharmacies, hardware stores, ordered through Internet sites. For industrial purposes, purchased in bulk with discounts. The average cost for Moscow in rubles is:


Quantity, liter

Average price, p.

Thermal food



Technical 85%





Soldering flux





Food supplement E388



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