Phosphoric Acid - Formula, Uses, Properties, Preparation, FAQs

Orthophosphoric Acid - H₃HO₄ (Phosphoric Acid)

Phosphoric acid is referred to as orthophosphoric acid. Phosphoric acid has the chemical formula H₃PO₄ and is a weak acid. Phosphoric acid is an acid with four oxygen atoms, one phosphorus atom, and three hydrogen atoms. Phosphoric(V) acid or orthophosphoric acid are other names for it. It can be found in teeth and bones, and it aids in metabolic activities. It appears as a clear, colourless solution in liquid form and as a transparent, crystalline solid in solid form.

Also Phosphoric acid formula or phosphoric acid chemical formula is PO₄ and Orthophosphoric acid formula is H₃PO₄ similarly phosphorous acid formula is H₃PO₄; Phosphorous acid is also known Orthophosphorous acid. It aids in the binding of divalent cations as a sequestering agent. In orthodontics and dentistry, it is commonly employed. In biogeochemistry and biochemistry, phosphoric acid plays a significant role. It's called tribasic acid. The three zones are the one where pH equals pK, the one where pH equals 4.7, and the one where pH is equal to 9.8.

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Preparation of Phosphoric Acid

It's easy to make by dissolving P₂O₅ in water and then heating the solution to make a thick syrup.

P₂O₅ + 3H₂O → 2H₂PO₄

When red phosphorus is cooked with conc.HNO₃, orthophosphoric acid is formed.

P + 5HNO₃ → H₃PO₄ + H₂O + 5NO₂

It is produced on a big scale by processing phosphorite rock with dilute H₂SO₄.

Ca₃(PO₄)₂ + 3H₂SO₄ → 3CaSO₄ + 2H₃PO₄

Synthesis of Phosphoric Acid – H₃PO₄

Sulphuric acid is added to the phosphate of baryta suspended in water, and the sulphuric acid reacts with the baryta to generate an insoluble salt that precipitates while the phosphoric acid stays in solution. When phosphorus is slowly added to nitric acid, phosphoric acid is formed, which is mixed with the remaining nitric acid.

Physical Properties of Phosphoric Acid (H₃PO₄)

1. Phosphoric acid is an odourless, colourless, viscous liquid with a high degree of reddening litmus property. It cannot be obtained without the use of water.

2. When a transparent fragile glass is subjected to red heat and then cooled, it develops.

3. Because phosphoric acid damages glass and porcelain when heated to redness, this fusion should be done in a platinum crucible.

4. When the acid is studied after being exposed to heat, it is shown to have acquired new qualities, despite the fact that its composition remains unchanged.

5. It has been given the label para phosphoric as a result of this, while the term phosphoric is used to refer to the acid in the first stated condition.

6. Silver nitrate produces a yellow precipitate with phosphoric acid and a white precipitate with para phosphoric acid. The latter, but not the former, coagulates albumen.

Chemical Properties of Phosphoric Acid (H₃PO₄)

Phosphoric acid is a solid that is commonly found in a viscous aqueous solution.

1. It is slightly acidic, with three probable deprotonation stages leading to the formation of phosphates.

2. Phosphoric acid, like carboxylic acids, can dimerize to generate phospho anhydrides by a dehydration reaction.

3. Phosphoric acid is classified as tribasic because it can dissociate into three different forms.

4. As a result, phosphoric acid mono, disodium, and potassium salts are commonly utilised as pH buffers.

5. Multimerization is one of the most important reactions involving phosphoric acid and its derivatives.

6. Two phosphoric acid molecules may interact with the loss of water to generate a diphosphate ester, also known as pyrophosphate, similar to carboxylic acids.

7. However, because phosphoric acid has more -OH functions, triphosphates can form.

8. Phosphoric acid salts are solid and, unless a strong mineral acid is present, many are generally water insoluble.

Basicity of Orthophosphoric Acid (H₃PO₄)

The quantity of hydrogen atoms that can be substituted by electro – positive atoms determines an acid's basicity. The quantity of hydrogen ions that can be created by ionising one molecule of an acid in its aqueous solution is known as basicity. A tribasic acid, also known as a triprotic acid, is an acid that creates three hydrogen or hydronium ions when one molecule of the acid is ionised. H₃PO₄ and H₃PO₃ are tribasic acids, for example.

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Uses of Phosphoric Acid (H₃PO₄)

Phosphoric acid (H₃PO₄) is used in a variety of ways, including the production of fertilisers. Many acids are made from phosphate rocks via a wet process that involves phosphate rocks reacting with acid solutions. H₃PO₄ is a medium-strong acid that is very corrosive to ferrous and ferrous alloys.

1. It is used in fertilisers - approximately 90% of the phosphoric acid generated is utilised in fertilisers.

2. It's a supplement feed for pigs, cattle, and poultry.

3. It is used as a pH adjuster in skincare and cosmetics.

4. It is used as a sanitising agent in the brewing, food, and dairy sectors.

5. It is used to acidify beverages and foods such as jam and cola.

6. It is used to eliminate rust from metals surfaces.

Health Hazard

Concentrated sulphuric or nitric acid are more corrosive and dangerous than phosphoric acid. The skin and mucous membranes are irritated by its concentrated solutions. P₂O₅ fumes in the vapours can irritate the throat and induce coughing, however at 10mg/m³ they might be tolerated. Phosphoric acid, in both solid and liquid form, is noncombustible. If inhaled, it can be lethal. Fire smoke contains phosphine, phosphoric acid, and hydrogen chloride, which can irritate respiratory passages, eyes, and skin.

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NCERT Chemistry Notes:

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