Phosphoric acid and polyphosphoric acid are two compounds that contain phosphorus, oxygen, and hydrogen atoms. However, there is a difference in their structure, which make them possess different chemical properties.
What is the difference between phosphoric acid and polyphosphoric acid? Phosphoric acid is a simple molecule with one phosphorus atom, four oxygen atoms, and three hydrogen atoms, whereas polyphosphoric acid is a complex mixture of phosphoric acid molecules linked together through oxygen atoms.
Key Areas Covered
1. What is Phosphoric Acid
– Definition, Features, Uses
2. What is Polyphosphoric Acid
– Definition, Features, Uses
3. Similarities Between Phosphoric Acid and Polyphosphoric Acid
– Outline of Common Features
4. Difference Between Phosphoric Acid and Polyphosphoric Acid
– Comparison of Key Differences
5. FAQ: Phosphoric Acid and Polyphosphoric Acid
– Answers to Frequently Asked Questions
Key Terms
Phosphoric Acid, Polyphosphoric Acid
What is Phosphoric Acid
Phosphoric acid is an inorganic compound with the chemical formula H₃PO₄. It is colorless, non-volatile, and odorless. It is a solid. Phosphoric acid is hygroscopic, as well.
Phosphoric acid is a weak acid because it partially ionizes in water to release hydrogen ions. It is a tribasic acid as it can donate 3 protons in successive steps. That is, ionization occurs in three stages.
H₃PO₄ ↔ H⁺ + H₂PO₄⁻
H₂PO₄⁻ ↔ H⁺ + HPO₄²⁻
HPO₄²⁻ ↔ H⁺ + PO₄³⁻
Phosphoric acid participates in various chemical reactions. They react with bases to form salts like sodium phosphate or calcium phosphate. It also undergoes dehydration to form polyphosphoric acids. Phosphoric acids react with alcohol to form phosphate esters. Sometimes, phosphoric acid is reduced to form phosphoric acid.
What is Polyphosphoric Acid
Polyphosphoric acid (PPA) is a complex mixture of phosphoric acids. It has multiple phosphorus atoms linked together through oxygen bridges. It does not have one specific formula, and it is not a single compound. Instead, it is a range of compounds with different average molecular weights.
PPA can be produced by heating orthophosphoric acid (H₃PO₄) to high temperatures. This process results in the condensation of phosphoric acid and the elimination of water molecules.
A variety of polyphosphoric acids, including pyrophosphoric acid (H₄P₂O₇), tripolyphosphoric acid (H₅P₃O₁₀), and longer chain polyphosphoric acids are present in the resulting mixture.
Phosphoric acid has many uses in industry. It is mainly used in organic chemistry as a catalyst. This is mainly due to its dehydrating properties. This catalytic property is useful in alkylation, acylation and condensation. PPA also helps in the production of organic compounds such as plastics, pharmaceuticals and dyes. In the petroleum industry, PPA is involved in processes such as dehydration, polymerization, alkylation, and isomerization.
Similarities Between Phosphoric Acid and Polyphosphoric Acid
- Both compounds contain phosphorus, oxygen, and hydrogen atoms.
- Both are acidic compounds capable of donating protons (H+) in aqueous solutions.
- Polyphosphoric acid is derived from phosphoric acid through a dehydration process.
- Both are corrosive substances.
Difference Between Phosphoric Acid and Polyphosphoric Acid
Definition
- Phosphoric acid is a single molecule with one phosphorus atom, four oxygen atoms, and three hydrogen atoms, while polyphosphoric acid is a mixture of multiple phosphoric acid molecules linked together.
Chemical Formula
- Phosphoric acid has the chemical formula H₃PO₄, while polyphosphoric acid has no specific formula, as it’s a mixture of compounds.
Viscosity
- Phosphoric acid has a lower viscosity than that of polyphosphoric acid.
Strength
- Polyphosphoric acid is generally a stronger acid than phosphoric acid.
Form
- Phosphoric acid can be obtained in pure form, while polyphosphoric acid is always a mixture of different phosphoric acid molecules.
Conclusion
Phosphoric acid is a single molecule with one phosphorus atom, while polyphosphoric acid is a chain of multiple phosphorus atoms linked by oxygen atoms. Moreover, polyphosphoric acid is a polymer of phosphoric acid. This is the basic difference between phosphoric acid and polyphosphoric acid.
FAQ: Phosphoric Acid and Polyphosphoric Acid
1. Are phosphoric acid and phosphonic acid the same?
Phosphoric acid and phosphonic acid are not the same. Phosphoric acid has the formula H3PO4, while phosphonic acid (often called phosphorous acid) has the formula H3PO3. They differ in their structure and properties.
2. What is the difference between phosphoric acid and metaphosphoric acid?
Phosphoric acid is a tribasic acid with three acidic hydrogen atoms while metaphosphoric acid is a cyclic polymer of phosphoric acid units, existing in various ring sizes.
3. What is another name for phosphoric acid?
Phosphoric acid is also known as orthophosphoric acid. It’s a common name used to differentiate it from other forms of phosphoric acids like polyphosphoric acid.
4. How to make polyphosphoric acid?
Polyphosphoric acid is made by dehydrating phosphoric acid. This can be done by heating it to high temperatures or by reacting it with phosphorus pentoxide. The process involves removing water molecules from phosphoric acid, leading to the formation of longer chains of phosphate groups.
5. What is the structure of a polyphosphoric acid?
Polyphosphoric acid consists of a linear chain of alternating phosphorus (P) and oxygen (O) atoms. Each phosphorus atom is bonded to three oxygen atoms, with one oxygen bridging to the next phosphorus in the chain. Moreover, the remaining oxygen atoms on each phosphorus are bonded to hydrogen atoms, forming hydroxyl groups.
Reference:
1. “Phosphoric Acid.” Encyclopedia Britannica.
2. “Polyphosphoric Acid.” Science Direct.
Image Courtesy:
1. “Phosphoric-acid-2D-dimensions” (Public Domain) via Commons Wikimedia
2. “Polyphosphoric acid” By Diphosphorsäure_-_Diphosphoric_acid.svg: NEUROtikerderivative work: Daniele Pugliesi (talk) – Diphosphorsäure_-_Diphosphoric_acid.svg (Public Domain) via Commons Wikimedia
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