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VOOZH | about |
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VOOZH | about |
Phosphoric acid is a colorless, odorless, inorganic compound. It is mainly found as an aqueous solution with a concentration of about 85%. It is represented by the chemical formula H3PO4. It is extensively used in distinct fields. Its applications include its usage in manufacturing fertilizers, various pharmaceutical products, skin care products, and much more.
In this article, we will do an in-depth study of Phosphoric acids, their properties, their usage, and others in detail.
Table of Content
Phosphoric Acid Overview | |
|---|---|
IUPAC Name | Ortho Phosphoric Acid |
Chemical Formula | H3PO4 |
Molar Mass | 97.99 g/mol |
Melting Point | 42.4 °C OR 108.3 °F OR 315.5 K |
Boiling Point | 407 °C OR 765 °F OR 680 K |
Phosphoric acid is a weak inorganic acid which is colorless and odorless. It is generally found in a liquid state with a concentration of not more than 85%. It is found as a white solid crystal solid in its pure form. The IUPAC name of Phosphoric Acid is orthophosphoric acid.
The conjugate base of phosphoric acid is Dihydrogen phosphate. The structure of its crystal is monoclinic and its molecular shape is tetrahedral. It is a non-poisonous and non-toxic acid in low concentrations but can be dangerous in high concentrations. Various properties of Phosphoric Acid are,
Phosphoric Acid consists of three hydrogen atoms, one phosphorous atom along with four oxygen atoms.
Chemical Formula of Phosphoric Acid is H3PO4
The chemical name of phosphoric acid is orthophosphoric acid.
The molecular weight of phosphoric acid is 97.99 g/mol.
Calculation of Molecular Weight
We can easily calculate the equivalent weight of phosphoric acid with the help of the following formula:
Equivalent Weight = Molecular Weight/Number of electrons
Since the molecular weight of Phosphoric acid is 97.99 g/mol and number of replaceable hydrogen ions in the acid is 2. By using the equivalent weight formula for phosphoric acid we get:
97.99/2 = 48.99 ≈ 49 g/mol
The equivalent weight of phosphoric acid is 49 g/mol.
Phosphoric acid is represented as H3PO4 or PO-(OH)3. The structure of Phosphoric Acid consists of three hydroxyl groups (-OH), each single-bonded with the central phosphorus atom (P) and one oxygen atom which is in double-bond with the central available phosphorus atom (P). The structure of Phosphoric acid is illustrated below:
In the Lewis structure, the bonded electrons are shown with a solid line, and non-bonded electrons are shown with the dots. The structure of phosphoric acid consists of one oxygen atom, one phosphorus atom, and three hydroxyl group (-OH). The Lewis structure of Phosphoric Acid is shown below:
👁 Phosphoric-Acid-Lewis-Structure
Here, each oxygen atom has 2 lone pairs, and the rest of the other electrons of each atom are bonded.
Phosphoric Acid has many applications and it is generally prepared by the two processes namely:
In wet process, phosphoric acid is produced from a naturally occurring crystal rock Fluorapatite. This crystal contains the phosphate mineral. Fluorapatite is reacted with concentrated sulphuric acid (H2SO4) and water (H2O). This reaction results in the formation of phosphoric acid and calcium sulfate (gypsum) along with some insoluble impurities. The reaction occuring in wet process is as follows:
Ca5(PO4)3Cl + 5H2SO4 + 10H2O → 3H3PO4 + 5CaSO4·2H2O + HCl
The side products and impurities formed during this reaction can be removed by the process of filtration and evaporation. Then by vacuum distillation this acid is concentrated to ca 56-70% P2O5 (super phosphoric acid). The impure product formed by the wet process can be used as fertilizer manufacture without any further purification.
Thermal process is another method used to obtain phosphoric acid. This process is helpful in obtaining a purer form of phosphoric acid. In this process,a phosphorus rock along with coke is heated or burnt at high temperature (about 2000 ℃ ) in a furnace in the presence of air. This results in the formation of phosphorus pentoxide which is further condensed to form a white powder. It is then hydrated to obtain phosphoric acid. The reaction occuring in wet process is as follows:
Step 1: Formation of phosphorus pentoxide
P4 + 5O2 → 2P2O5
Step 2: Hydration of phosphorus pentoxide
P2O5 + 3H2O → 2H3PO4
We can also obtain a condensed form of polyphosphoric acids by passing the steam to the burner. The products from the burner are then moved into a hydration tower to obtain phosphoric acid as the gaseous phosphorus oxide is absorbed there. The phosphoric acid obtained by thermal process is more pure ranging from 75 - 80%.
The types of Phosphoric acid is given below:
- Orthophosphoric acid is the other name of phosphoric acid, with oxidation state of +5.
- The prefix ortho is used to distinguish the acid from other related phosphoric acids, called polyphosphoric acids.
- The chemical formula of orthophosphoric acid is H3PO4.
- Hypophosphoric acid is a type of phosphoric acid which has a oxidation state of +4.
- It is a mineral and tetra basic acid which is formed due to the slow oxidation of phosphorus in moist air.
- The chemical formula of hypophosphoric acid is H4P2O6.
- Metaphosphoric acid is a type of phosphoric acid which has a oxidation state of +5.
- It is an inorganic, corrosive, cyclic acid formed from bonded phosphoric acid units.
- The chemical formula of metaphosphoric acid is HPO3.
The physical and chemical properties of Phosphoric Acid are described below:
Some physical properties of the Phosphoric Acid are,
Some Chemical Properties of Phosphoric Acid are,
H3PO4 + H2O ⇋ 3H+ + PO43-
Its reaction with sodium hydroxide results in the formation of three types of salts namely Na2HPO4, NaH2PO4, and Na3PO4. One of the reaction equation is given below:
NaOH + H3PO4 → NaH2PO4 + H2O
Phosphoric acid, also known as H3PO4 is a non-metal phosphate. It is an inorganic weak acid but long exposure to it can result into irritation in skin and eyes.
Phosphoric acid consists of three H+ ions. Removal of three H+ ions, two H+ ions or one H+ ion gives out the phosphate ion (PO43-), hydrogen phosphate ion (HPO42-) and dihydrogen phosphate ion (H2PO4-) respectively.
Hence it can serve properties of both acidic and basic. Its pH value at different concentrations is given below:
Total moles of pure H3PO4 per Litre | Concentration (%) | pH |
|---|---|---|
|
1 |
91.7 |
1.08 |
|
10-1 |
76.1 |
1.62 |
|
10-2 |
43.1 |
2.25 |
|
10-3 |
10.6 |
3.05 |
|
10-4 |
1.30 |
4.01 |
|
10-5 |
0.133 |
5.00 |
|
10-6 |
1.34 × 10-2 |
5.97 |
|
10-7 |
1.80 × 10-3 |
6.74 |
|
10-10 |
8.24 × 10-4 |
7.00 |
The salts of phosphoric acid are termed as Phosphates. The important phosphates of Phosphoric Acid are:
Calcium phosphate also known as superphosphate is formed by the reaction of phosphate rock with sulphuric acid. It is mainly used as a fertilizer. The chemical reaction involved in the formation of calcium phosphate is:
Ca3(PO4)2 + H2SO4→Ca(H2PO4)2 + 2CaSO4
Ammonium phosphate is formed by combining phosphoric acid with anhydrous ammonia in adequate quantity. Diammonium hydrogen phosphate and monoammonium dihydrogen phosphate are types of ammonium phosphate which are used as fertilizers to increase the amount of nitrogen and phosphorus in crops.
Sodium phosphates are solid crystals that are formed by the reaction of phosphoric acid with concentrated solution of sodium hydroxide. Disodium hydrogen phosphate, Disodium pyrophosphate, Trisodium phosphate, and Monosodium dihydrogen phosphate are some examples of sodium phosphate.
Phosphoric Acid has a wide range of applications in diverse industries. A few of its uses are described below:
Phosphoric acid act as a good rust remover and therefore it is used as a treatment of rust. When phosphoric acid reacts with iron oxide it forms a protective layer and thus prevents rusting.
Phosphoric Acid is also used in soft drinks and in various other food and beverages as an acidity regulator and to enhance their flavor and taste, it gives a special tart flavour to these products.
Phosphoric Acid fuel cell (PAFC) uses liquid phosphoric acid as an electrolyte. This liquid phosphoric acid helps in improving stability and performance of the fuel cell. It is also cost efficient and provides an efficiency of about 35% - 45%.
Some other uses of phosphoric acid are:
In General, phosphoric acid is non-toxic and non-poisonous and is harmless when used in low concentrations. However, it is dangerous at high concentrations and can cause severe damage and irritation to the skin and eyes if exposed. It can even harm the respiratory tract if its vapors are inhaled. Therefore, it should be stored in a cool and ventilated place in a metal container and proper care and precautions must be taken while handling it.
IUPAC Name | Ortho Phosphoric Acid |
|---|---|
Chemical Formula | H3PO4 |
Melting Point | 42.4 °C |
Boiling Point | 407 °C |
Molecular Weight | 97.99 g/mol |
Equivalent Weight | 49 g/mol |
Appearance | Colourless liquid |
Odor | Odorless |
pKa value |
|
Density | 1.6845 g/cm3 |
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