Question

Fuming sulfuric acid is formed when sulfur trioxide dissolves in anhydrous sulfuric acid to form \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7} .\) Propose a structure for \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}\), which contains an \(\mathrm{S}-\mathrm{O}-\mathrm{S}\) linkage.

Short answer

H₂S₂O₇ has an \(\text{S-O-S}\) with each \(\text{S}\) bonded to \(2\text{ =O}\) and \(1\text{-OH}\).

Step-by-step solution

Understand the Components

Fuming sulfuric acid, also known as oleum, is produced by dissolving sulfur trioxide \(\text{SO}_3\) in anhydrous sulfuric acid (\(\text{H}_2\text{SO}_4\)). The resulting product, \(\text{H}_2\text{S}_2\text{O}_7\), has a specific structure that includes an \(\text{S-O-S}\) linkage.

Identify the Number of Each Atom in the Molecule

The molecular formula \(\text{H}_2\text{S}_2\text{O}_7\) indicates that the compound consists of 2 hydrogen atoms, 2 sulfur atoms, and 7 oxygen atoms. Our task is to arrange these atoms into a structure that satisfies this composition.

Incorporate the \(\text{S-O-S}\) Linkage

According to the problem statement, \(\text{H}_2\text{S}_2\text{O}_7\) must contain an \(\text{S-O-S}\) linkage. This means that two sulfur atoms are connected by an oxygen atom, forming the backbone of the molecule: \(\text{S-O-S}\).

Construct the Main Structure

Each sulfur atom typically forms tetrahedral bonds with four oxygen atoms. In \(\text{H}_2\text{S}_2\text{O}_7\), one central oxygen links the two sulfur atoms. Therefore, start by connecting the sulfurs with an oxygen: \(\text{S-O-S}\). Each sulfur will separately bond with three more oxygens.

Add Remaining Oxygens and Hydrogens

For each sulfur, one of the oxygen atoms will be double-bonded, making the typical \(\text{S=O}\) segments. The remaining two oxygen atoms on each \(\text{SO}_3\) group will form \(\text{-OH}\) groups by bonding to hydrogen atoms. Confirm the molecule structure as: \((\text{HO}-\text{S}(=\text{O})_2-\text{O}-\text{S}(=\text{O})_2-\text{OH})\). This represents disulfuric acid.

Key concepts

Fuming sulfuric acid

Fuming sulfuric acid, commonly known as oleum, is a chemical substance that represents a mixture of sulfuric acid (\(\text{H}_2\text{SO}_4\)) and sulfur trioxide (\(\text{SO}_3\)). This combination results in a solution that is more chemically potent than regular sulfuric acid.
It is called "fuming" because it releases white fumes when exposed to air. These fumes are actually traces of \(\text{SO}_3\) that escape from the liquid. This substance plays a crucial role in industrial applications, particularly in the production of explosives, dyes, and other chemicals.

• The strength of fuming sulfuric acid is commonly expressed in terms of its free \(\text{SO}_3\) content.
• It varies in its concentration, with higher concentrations releasing more \(\text{SO}_3\).

Due to its reactivity, fuming sulfuric acid must be handled with care as it can cause severe chemical burns.

Oleum chemistry

Oleum, another name for fuming sulfuric acid, involves interesting chemistry due to its unique structure and composition. In the process of forming oleum, sulfur trioxide (\(\text{SO}_3\)) dissolves in sulfuric acid, leading to the formation of disulfuric acid (\(\text{H}_2\text{S}_2\text{O}_7\)).
This compound is noteworthy because it can also serve as a source of free \(\text{SO}_3\), which can be used in further chemical reactions.

• Oleum exists in different "grades" depending on how much \(\text{SO}_3\) is dissolved.
• It can be designed with variable concentrations, allowing flexibility for industrial use.

Oleum chemistry is particularly essential in the sulfuric acid production cycle, where it acts as an intermediate step to produce higher concentrations of sulfuric acid.

Sulfur-oxygen bond

The sulfur-oxygen bond is essential to understanding the structure and reactivity of disulfuric acid. In \(\text{H}_2\text{S}_2\text{O}_7\), two sulfur atoms are connected through an oxygen atom, forming a bridging \(\text{S-O-S}\) linkage. This formation is crucial for disulfuric acid's properties.
Sulfur atoms can have varying oxidation states, and in disulfuric acid, the sulfur atoms are typically in a high oxidation state, allowing them to form multiple bonds with oxygen atoms.

• In each \(\text{SO}_3\) group, the sulfur atom forms double bonds with one of its oxygen partners, known as the \(\text{S=O}\) bond.
• Another two oxygen atoms are involved in forming hydroxyl (\(-OH\)) groups.

The unique \(\text{S-O-S}\) linkage provides distinguishing characteristics that contribute to the chemical behavior of disulfuric acid. Understanding these bonds is key in oleum's chemistry and related industrial processes.