What is the difference between phosphoric acid and metaphosphoric acid?

Orthophosphoric acid is a type of phosphoric acid with the difference in structure. Orthophosphoric acid is a phosphoric acid composed of a single phosphorus-oxygen tetrahedron. In the phosphoric acid molecule, the P atom is sp3 hybridized, three hybrid orbitals form three sigma bonds with the oxygen atom, and the other P-O bond is composed of a sigma bond from phosphorus to oxygen and two from oxygen to Phosphorus consists of d-pπ bonds. The σ-bonding bond is formed by the coordination of a pair of lone pairs of electrons on a phosphorus atom to an empty orbital of an oxygen atom. The d←p bond is formed by overlapping two pairs of lone pairs of electrons in the py and pz orbitals of the oxygen atom and the dxz and dyz orbits of the phosphorus atom. Since the 3d energy level of the phosphorus atom is much higher than the 2p energy level of the oxygen atom, the molecular orbital of the composition is not very effective, so the P-O bond is a triple bond in terms of number. But in terms of bond energy and bond length, it is referred to between single and double keys. The orthophosphoric acid industry is treated with sulfuric acid to obtain apatite.

H3PO2, hypophosphorous acid, where in the oxidation number of phosphorus is positive one;

H3PO3, phosphorous acid, where in the oxidation number of phosphorus is positive three;

H3PO4, orthophosphoric acid, where in the oxidation number of phosphorus is positive five. In the orthophosphoric acid molecule, only one phosphorus-oxygen bond is called a triple bond, which is also called a coordinate bond, and another three phosphorus-oxygen covalent single bonds are directly connected to hydrogen, that is, three hydroxyl groups;

The phosphorous acid molecule has a hydrogen atom directly sharing an electron pair with a phosphorus atom, a phosphorus-oxygen coordinate bond, and a POH bond;

In the hypophosphorous acid molecule, there are two hydrogen atoms directly sharing an electron pair with a phosphorus atom, a phosphorus-oxygen coordinate bond, and two POH bonds;

According to the theory of delocalization, one PO coordination bond is for one hydroxyl group, one phosphorus-oxygen coordination bond is for two hydroxyl groups, and one phosphorus-oxygen coordination bond is for three hydroxyl groups, then the acidity is hypophosphorous acid > phosphorous acid > phosphoric acid . That is to say, the degree of ionization of hydrogen atoms in the hydroxyl group is stronger than that of phosphorous acid than phosphoric acid.

Phosphoric acid groups generally appear in organisms. It generally referred to as acyl phosphates, ie, structures in which one hydroxy group is removed by phosphoric acid, or a phosphate group from which two hydroxy groups are removed. Such structures are found in many cellular active substances, such as ATP, nucleotides, etc.

Phosphoric acid refers to inorganic phosphoric acid. In living organisms is meant free phosphoric acid.

Phosphonic acid,

It is a compound in which one or two hydroxyl groups in the phosphoric acid (HO) 3PO molecule are substituted by an alkyl group or an aryl group.

Pure phosphoric acid is a colorless crystal with a melting point of 42.3 ° C, a high boiling point acid, and is readily soluble in water. Phosphoric acid commercially available phosphoric acid reagents are viscous, non-volatile concentrated solutions with a phosphoric acid content of 83-98%.

Phosphate

Phosphoric acid or orthophosphoric acid, the chemical formula H3PO4, has a molecular weight of 97.9724 and is a common inorganic acid which is a medium strong acid. It can be obtained by dissolving tetraphosphorus tetraoxide in hot water. The orthophosphoric acid industry is treated with sulfuric acid to obtain apatite. Phosphoric acid is easily deliquescent in the air. Heating will lose water to get pyrophosphoric acid, and further lose water to get metaphosphoric acid. Phosphoric acid is mainly used in the pharmaceutical, food, fertilizer and other industries, and can also be used as a chemical reagent.

Physical properties

Melting point: 42 ° C

Boiling point: 261 ° C (decomposition, phosphoric acid is gradually dehydrated by heat, so there is no boiling point of its own)

P2O5 and cold water produce metaphosphoric acid, and hot water is phosphoric acid. Phosphoric acid and AgNO3 produce a yellow precipitate, and metaphosphoric acid produces a white precipitate. However, only metaphosphoric acid can agglomerate the aqueous protein solution to produce a white precipitate.

The most critical point: phosphoric acid is non-toxic and metaphosphoric acid is highly toxic.

The orthophosphoric acid and AgNO3 produced a yellow precipitate, and the metaphosphoric acid produced a white precipitate. However, only metaphosphoric acid can agglomerate the aqueous protein solution to produce a white precipitate.

Phosphoric acid or orthophosphoric acid, the chemical formula H3PO4, has a molecular weight of 97.994, is a common inorganic acid and is a medium strong acid. It can be obtained by dissolving phosphorus pentoxide in hot water. The orthophosphoric acid industry is treated with sulfuric acid to obtain apatite. Phosphoric acid is easily deliquescent in the air. Heating will lose water to get pyrophosphoric acid, and further lose water to get metaphosphoric acid. Phosphoric acid is mainly used in the pharmaceutical, food, fertilizer and other industries, including as a rust inhibitor, food additive, dental and orthopedics, EDIC corrosives, electrolytes, fluxes, dispersants, industrial corrosives, fertilizer raw materials and components household cleaning products. It can also be used as a chemical reagent, and phosphate is a nutrient for all life forms.

After the German businessman Poland discovered phosphorus and the German chemist Conkell produced phosphorus, the British chemist Boyle also produced phosphorus independently. He was also the first chemist to study phosphorus properties and compounds. He published in 1682. The paper "A New Experiment of Observed Cold Light" states that "Phosphorus forms white smoke after combustion, and the solution formed by the action of white smoke and water is acidic." The white smoke is phosphoric anhydride (phosphorus pentoxide). ), and the solution formed by the action of water is phosphoric acid, however, he did not conduct further research on phosphoric acid.

The earliest chemist to study phosphoric acid was the French chemist Lavoisier. In 1772 he did the experiment of burning phosphorus in a bell jar sealed with mercury. The experimental results lead to the conclusion that a certain amount of phosphorus can be burned in a certain volume of air; when the phosphorus burns, a white powder of anhydrous phosphorus is formed, such as fine snow; the air in the bottle after burning is about the original capacity. 80%; phosphorus burns about 2.5 times more than before burning; white powder is dissolved in water to form phosphoric acid. Lavoisier also proves that phosphoric acid can be obtained by reacting concentrated nitric acid and phosphorus.

After more than a hundred years, the German chemist Liebig has done many experiments in agricultural chemistry, uncovering the value of phosphorus and phosphoric acid for plant life. In 1840, Li Bixi's "The Role of Organic Chemistry in Agriculture and Physiology" scientifically demonstrated the soil fertility problem and pointed out the role of phosphorus in plants. At the same time, he further explored the application of phosphoric acid and phosphate as fertilizers, and the production of phosphoric acid has entered a large-scale era.

Orthophosphoric acid is a phosphoric acid composed of a single phosphorus-oxygen tetrahedron. In the phosphoric acid molecule, the P atom is sp3 hybridized, three hybrid orbitals form three sigma bonds with the oxygen atom, and the other P-O bond is composed of a sigma bond from phosphorus to oxygen and two from oxygen to Phosphorus consists of d-pπ bonds. The σ-bonding bond is formed by the coordination of a pair of lone pairs of electrons on a phosphorus atom to an empty orbital of an oxygen atom. The d←p bond is formed by overlapping two pairs of lone pairs of electrons in the py and pz orbitals of the oxygen atom and the dxz and dyz orbits of the phosphorus atom. Since the 3d energy level of the phosphorus atom is much higher than the 2p energy level of the oxygen atom, the molecular orbital of the composition is not very effective, so the P-O bond is a triple bond in terms of number, but in terms of bond energy and bond length, it is referred to between single and double keys. There are hydrogen bonds in pure H3PO4 and its crystalline hydrates, which may be the reason why the concentrated phosphoric acid solution is thick.

Melting point: 42 ° C

Boiling point: 261 ° C (decomposition, phosphoric acid is gradually dehydrated by heat, so there is no boiling point of its own)

Commercially available phosphoric acid is a viscous concentrated solution containing 85% H3PO4. Crystallization from the concentrated solution formed the hemihydrate 2H3PO4.H2O (melting point 302.3K).

Knot (ice) crystal point:

Phosphoric acid is a medium-strong acid with a crystallization point (freezing point) of 21 ° C. When it is below this temperature, hemihydrate (ice) crystals are precipitated. Of course, phosphoric acid usually does not freeze (ice) crystals at temperatures above 10 ° C or even lower, because phosphoric acid has a supercooling property, that is, commercially available phosphoric acid deviates from its knot below 21 ° C (ice The crystal point does not immediately form an ice crystal. However, as long as such a low temperature is maintained for a while, phosphoric acid is liable to generate knot (ice) crystals in a static state.

Phosphoric acid crystallization is a physical change rather than a chemical change like other liquid crystals. The chemical properties are not changed by crystallization, that is, the quality of phosphoric acid is not affected by crystallization, and can be normally used as long as it is melted by temperature or diluted by heating water.

Crystallization characteristics: high phosphoric acid concentration, high purity, and high crystallinity. According to experience, when the temperature is above 4 degrees Celsius and the concentration is greater than 85%, the crystallinity increases. If the knot (ice) crystal phosphoric acid is inadvertently mixed, the phosphoric acid which has no knot (ice) crystal will be immediately infected and frozen. Crystal, and phosphoric acid (ice) crystals are abnormally fast, and the direct phosphoric acid storage container has a large knot (ice) crystal. After the phosphoric acid (ice) crystal, the upper phosphoric acid is thinned, and the needle-like knot (ice) crystal is deposited as pure phosphoric acid. As a rule of thumb, 75% phosphoric acid is also more difficult to freeze (ice) at lower temperatures (around 4 °C), so at lower temperatures it is recommended to use 75% phosphoric acid.

Phosphate (ice) crystals, like water ice, are physical properties that cannot be changed and can only be prevented by proper storage and treatment.

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