Phosphoric Acid | Advantages and Disadvantages of phosphoric acid

Phosphoric Acid

Organic Name - Phosphoric Acid

Molecular formula - H₃PO₄

Strength - Weak

Phosphoric acid is a weak acid that chemical formula is H₃PO₄. It is usually exposed to a colorless sherbet of 85% concentration in water. The pure compound is colorless hard. Although phosphoric acid does not meet the strict definition of a strong acid, an 85% solution can still cause severe skin irritation and eye damage.

Chemical structure of phosphoric acid

Phosphoric Acid Formation

Phosphoric acid is produced industrially by two common roots. In the wet process, calcium hydroxyapatite minerals are treated with sulfuric acid.

Ca₅ (PO₄)₃OH + 5 H₂SO₄ {\displaystyle {\ce {Ca5(PO4)3OH + 5H2SO4 -> 3H3PO4 + 5CaSO4v + H2O}}}   =         3 H₃PO₄ + 5 CaSO₄ + H₂O

                       

Fluoroapatite is an alternative feedstock, in which case the fluoride insoluble compound is removed as Na₂SiF₆. The phosphoric acid liquor normally contains 23–33% P₂O₅ (32–46% H₃PO₄). It can be concentrated in the production of commercial- or merchant-grade phosphoric acid, which contains about 54-62% P₂O₅. Further removal of water gives super phosphoric acid with a P₂O₅ concentration above 70%. Calcium sulfate (gypsum) is produced as a by-product and removed as phosphogypsum.

To produce food-grade phosphoric acid, the phosphate ore is first reduced by coke in an electric arc furnace, to produce primary phosphorus. Silica is also added, for this reason, the production of calcium silicate slag. Elemental phosphorus is distilled from the furnace and burned in air to form high purity phosphorus pentoxide, which is dissolved in water to form phosphoric acid.

Phosphoric acid from both processes can be further purified by removing compounds of arsenic and other potentially toxic impurities.

Properties-

1. Phosphoric acid comparatively weak acid

2. It is a colorless solid

3. Solubility in water 548g/100ml (20°C)

4. It is Odorless

5. Melting Point 40-42°C and boiling point 212°C

Acidic condition

Three hydrogens are acidic, with the separation constants pKa1 = 2.14, pKa2 = 7.20, and pKa3 = 12.37. It follows that in aqueous solutions, phosphoric acid is mostly isolated in some synthesis of its three anions, except at very low pH. The equations of equilibrium are:

            H₃PO₄   + H₂O = H₃O⁺ + H₂PO₄⁻      K_a1= 7.25×10⁻³ [pK_a1 = 2.14]

H₂PO₄⁻+ H₂O = H₃O⁺ + HPO₄²⁻       K_a2= 6.31×10⁻⁸ [pK_a2 = 7.20]

HPO₄²⁻+ H₂O = H₃O⁺ + PO₄³⁻        K_a3= 3.98×10⁻¹³ [pK_a3 = 12.37]

Advantages of phosphoric acid

1. It is used in the soaps and detergents industry.

2. It is used in foods and beverages.

3. It is used in soft drinks manufacturing.

4. It is used as a pH adjuster in cosmetics and skin-care products.

5. It is used as a sanitizing agent in the dairy, food, and brewing industries.

6. It is used in activated carbon production.

7. It is used in the washing industry for color removal purposes.

8. In textiles, it is used as an oxidizing agent. 

Disadvantages of phosphoric acid

1. It causes dental erosion.

2. It contributes to the formation of kidney stones.

3. Moderate concentrations of phosphoric acid solutions are irritating to the skin.

4. Concentrated solutions can cause severe skin burns and permanent eye damage.

Conclusion

At moderate concentrations, phosphoric acid solutions are irritating to the skin. Contact with concentrated solutions can cause severe skin burns and permanent eye damage.