Question

Which of the following statement is correct? (1) S-S bond is present in \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}\). (2) In peroxosulphuric acid \(\left(\mathrm{H}_{2} \mathrm{SO}_{5}\right)\) sulphur is in \(+8\) oxidation state. (3) Copper powder along with \(\mathrm{Al}_{2} \mathrm{O}_{3}\) and \(\mathrm{K}_{2} \mathrm{O}\) is used as a catalyst in the preparation of \(\mathrm{NH}_{3}\) by Haber's process. (4) Change in enthalpy is positive for the preparation of \(\mathrm{SO}_{3}\) by catalytic oxidation of \(\mathrm{SO}_{2}\).

Short answer

(1) is correct: S-S bond is present in \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}\).

Step-by-step solution

S-S bond in \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}\)

Analyze the molecular structure of \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}\). This molecule is known as dithionic acid. In dithionic acid, there indeed exists a bond between the two sulfur atoms, making statement (1) correct.

Checking Sulphur Oxidation State in \(H_{2}SO_{5}\)

Determine the oxidation state of sulfur in peroxosulphuric acid \(H_{2}SO_{5}\). The calculation is as follows: For \(H: +1\), \(O (normal): -2\), \(O (peroxo group): -1\). Oxidation state calculation: \[2(+1) + x + 3(-2) + 2(-1) = 0\] \[2 + x - 6 - 2 = 0\] \[x = +6\]. Sulfur is in the +6 oxidation state, so statement (2) is incorrect.

Catalyst in Haber's Process

Identify the catalyst used in the preparation of ammonia by the Haber process. Actually, iron combined with small amounts of K_2O, Al_2O_3, and calcium oxide is typically used as a catalyst, not copper. Therefore, statement (3) is incorrect.

Enthalpy Change in SO_3 Preparation

Examine the enthalpy change for the preparation of \(\mathrm{SO}_{3}\) by catalytic oxidation of \(\mathrm{SO}_{2}\): \[2\mathrm{SO}_{2}(g) + O_{2}(g) \rightarrow 2\mathrm{SO}_{3}(g)\]. This reaction is exothermic, meaning the change in enthalpy is negative, not positive. This makes statement (4) incorrect.

Key concepts

Understanding the S-S bond

The term 'S-S bond' refers to a bond between two sulfur atoms within a molecule. This bond is present in various sulfur compounds.

In the compound \(\text{H}_{2} \text{S}_{2} \text{O}_{6}\), known as dithionic acid, the S-S bond is indeed present. Dithionic acid is composed of two sulfur atoms bonded directly to each other, each bonded to two hydroxyl groups (OH) and connected to the oxygen atoms. This is a classic representation of sulfur-sulfur bonding in chemistry.

The significance of the S-S bond lies in its unique characteristics and its role in different chemical reactions. It's important to note how these bonds can influence the molecular configuration and the overall reactivity of the compound.

Oxidation State of Sulfur in Peroxosulfuric Acid

The oxidation state of an element in a compound is a concept that helps in understanding the electron exchange in oxidation-reduction reactions.

In peroxosulfuric acid \(\text{H}_{2} \text{SO}_{5}\), calculating the oxidation state of sulfur involves understanding the typical oxidation states of hydrogen and oxygen.

Here’s the breakdown:

• Hydrogen (\text{H}) typically has an oxidation state of \(+1\).
• Normal oxygen (\text{O}) atoms have an oxidation state of \(-2\).
• Oxygen in peroxo groups has an oxidation state of \(-1\).

By using the formula: \(\text{2}(+1) + x + 3(-2) + 2(-1) = 0\)
we find that: \(\text{x} = +6\).

Therefore, sulfur in \(\text{H}_{2} \text{SO}_{5}\) has an oxidation state of \(+6\), not \(+8\) as mentioned by some misstatements. This understanding helps in recognizing and correcting errors related to oxidation states in complex molecules.

Catalysts in Haber's Process

The Haber process is fundamental in the industrial production of ammonia \(\text{NH}_{3}\). This chemical reaction combines nitrogen \(\text{N}_{2}\) and hydrogen \(\text{H}_{2}\) gases under high pressure and temperature in the presence of a catalyst.

The primary catalyst used in the Haber process consists of iron (Fe) with promoters such as \(\text{K}_{2} \text{O}\), \(\text{Al}_{2} \text{O}_{3}\), and calcium oxide (CaO). These substances enhance the efficiency and effectiveness of the iron catalyst.

It is a common misconception that copper is used as a catalyst in this process. However, copper doesn't serve as the primary catalyst.
This catalyst setup is crucial for optimizing ammonia yield, which is vital in producing fertilizers and other chemicals. Understanding the role and composition of these catalysts helps in comprehending industrial chemical processes better.

Enthalpy Change in Catalytic Oxidation of SO2

Enthalpy change, denoted as \(\text{ΔH}\), represents the heat exchange in a chemical reaction.

For the preparation of sulfur trioxide (\text{SO}_{3}) by the catalytic oxidation of sulfur dioxide (\text{SO}_{2}), the chemical equation is:
\(\text{2 SO}_{2}(g) + \text{O}_{2}(g) \rightarrow \text{2 SO}_{3}(g)\)

This reaction is exothermic, meaning it releases heat, resulting in a negative enthalpy change.

\text{Enthalpy change details}:

• Exothermic reactions release heat, making \(\text{ΔH}\) negative.
• This contrasts with endothermic reactions, where heat is absorbed and \(\text{ΔH}\) is positive.

Understanding the enthalpy change is vital for predicting the energy dynamics and spontaneity of chemical reactions. It explains why the production of \(\text{SO}_{3}\) releases energy.