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Pyrosulfuric acid, also represented as H2S2O7, is the main constituent of fuming sulfuric acid. Disulfuric acid is another name for this acid. Having a molar mass of 178.13 g/mol, it is a dense, oily liquid that is formed by the union of sulfur trioxide with sulfuric acid and has a colourless to dark brown colour. It is also found in the form of hygroscopic solid. Prepared commercially, it is a heavy liquid that is used chiefly as a dehydrating agent in the manufacture of explosives. It is also used as a sulphating agent.
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Key Terms: Pyrosulfuric Acid, Pyrosulfuric Acid Formula, Hydrogen, concentrated sulfuric acid
Pyrosulfuric Acid Formula
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Pyrosulfuric acid is obtained by dissolving sulfur trioxide and concentrated sulfuric acid together. The chemical formula of pyrosulfuric acid is H2S2O7.The chemical reaction of the preparation can be represented as:
H2SO4 + SO3 → H2S2O7
As represented in the formula, the compound contains 2 hydrogen atoms. Since pyrosulfuric acid is an oxyacid of sulphur, it is also known by the name of oleum. Oleum is the most common form in which pyrosulfuric acid is found. The formula representation according to SMILES (Simplified Molecular Input Line Entry System) is OS(=O)(=O)OS(=O)(=O)O.
Pyrosulfuric Acid Formula
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Physical Properties of Pyrosulfuric Acid
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The physical properties of pyrosulfuric acid is as follows:
| IUPAC name | sulfo hydrogen sulfate |
| Chemical formula | H2S2O7 |
| Molecular weight | 178.129 g/mol |
| Melting point | 360C |
| Conjugate base | Disulfate |
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Chemical Properties of Pyrosulfuric Acid
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The chemical properties of pyrosulfuric acid is as follows:
- The chemical properties of this acid are very similar to sulfuric acid, except for the fact that it is a much weaker acid when compared to sulfuric acid.
- Pyrosulfuric acid reacts with bases quickly to from persulphates.
- When this acid goes through the process of decomposition, it produces sulpfuric acid and water. There is an elimination of sulfur trioxide.
- The conjugate base is the disulfate.
Pyrosulfuric Acid Applications
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The applications of pyrosulfuric acid are:
- It is used as a sulphating agent.
- It comes into use in the process of manufacturing explosives.
- It is also used in the dye industry.
- Since the transportation of sulfuric acid becomes difficult due to its corrosive nature, pyrosulfuric acid is often used as its substitute. It can be easily transported.
- It is also used in the process of petroleum refining.
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Things to Remember
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- Pyrosulfuric acid is the main constituent of fuming sulfuric acid.
- Disulfuric acid is another name for this acid.
- It has a molar mass of 178.13 g/mol.
- It is an oily and dense liquid in nature.
- Pyrosulfuric acid is obtained by dissolving sulfur trioxide and concentrated sulfuric acid together.
- Its IUPAC name is sulfo-hydrogen sulfate.
- Oleum is another name for pyrosulfuric acid.
- It is weaker than sulfuric acid.
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Ques. What are persulphates? (2 marks)
Ans. Prepared from the reaction between disulfuric acid and bases, persulphates are the salts of disulfuric acid. They are the key components in many industrial processes and commercial products. Persulphates are used as initiators in the polymerization of latex and synthetic rubber. The electronics industry uses sodium persulfate in the manufacture of printed circuit boards.
Ques. What are the chemical properties of pyrosulfuric acid? (2 marks)
Ans. The chemical properties of this acid are:
- Pyrosulfuric acid reacts with bases quickly to form persulphates.
- When this acid goes through the process of decomposition, it produces sulphuric acid and water. There is an elimination of sulfur trioxide.
- The conjugate base is the disulfate.
Ques. How is pyrosulfuric acid prepared? (2 marks)
Ans. Pyrosulfuric acid is obtained by dissolving sulfur trioxide and concentrated sulfuric acid together.The chemical reaction of the preparation of pyrosulfuric acid can be represented as: H2SO4 + SO3 = H2S2O7
Ques. With the help of a diagram, show the structure of pyrosulfuric acid. (2 marks)
Ans. The structure of pyrosulfuric acid is:
Ques. List down the uses of pyrosulfuric acid. (3 marks)
Ans. Pyrosulfuric acid has many applications:
- It is used as a sulphating agent.
- It comes into use in the process of manufacturing explosives.
- It is also used in the dye industry.
- Since the transportation of sulfuric acid becomes difficult due to its corrosive nature, pyrosulfuric acid is often used as its substitute. It can be easily transported.
- It is also used in the process of petroleum refining.
Ques. What is meant by catenation? Why does Carbon show the property of catenation to a maximum extent? (2 marks)
Ans. The phenomenon of an atom forming a strong covalent bond with the atoms of itself is known as catenation. Carbon shows the property of catenation to the maximum extent because carbon atoms are small in size and are capable of forming multiple Pπ -Pπ bonds with themselves.
Ques. Explain the differences in properties of diamond and graphite based upon their structures. (5 marks)
Ans. The differences between graphite and diamond are:
| Diamond | Graphite |
|---|---|
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Ques. How is boron obtained from borax? Give chemical equations with reaction conditions. (3 marks)
Ans.
Ques. CO2 is gas while SiO2 is solid at room temperature. Give reason. (2 marks)
Ans. A weak van der Waals force of attraction holds the molecules of CO2 together. Since this force of attraction is weak, it can be easily overcome by the collision of the molecules at room temperature. Hence, CO2 is a gas. Whereas, silicon atom forms four single covalent bonds with O-atom which are tetrahedrally arranged and form a three-dimensional structure. Thus SiO2 is a high melting solid.
Ques. When metal X is treated with sodium hydroxide, a white precipitate (A) is obtained, which is soluble in excess of NaOH to give soluble complex (B). Compound (A) is soluble in dilute HCl to form compound (C). The compound (A) when heated strongly gives (D), which is used to extract the metal. Identify (X), (A), (B), (C) and (D). Write suitable equations to support their identities. ((5 marks)
Ans.
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