Problem 20 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The amount of water produced (in g) in the oxidation of 1 mole of rhombic sulphur by conc. \(\mathrm{HNO}_{3}\) to a compound with the highest oxidation state of sulphur is \((\) Given data : Molar mass of water = \(\left.18 \mathrm{~g} \mathrm{~mol}^{-1}\right)\) [Adv. 2019]

Step-by-Step Solution

Answer

36 grams of water are produced.

Step 1: Determine the Reaction

When rhombic sulfur (S) is oxidized by concentrated nitric acid (HNO₃), sulfur is converted to its highest oxidation state of +6, forming sulfuric acid (H₂SO₄). The reaction also produces nitrogen dioxide and water. The overall balanced chemical reaction can be written as:\[ \begin{align*} S + 6 \text{HNO}_3 & \rightarrow H_2\text{SO}_4 + 6 \text{NO}_2 + 2 \text{H}_2\text{O} \end{align*} \]

Step 2: Calculate Water Production per Mole of Sulfur

From the balanced chemical equation in Step 1, we can see that for every 1 mole of sulfur oxidized, 2 moles of water (H₂O) are produced.

Step 3: Determine Grams of Water Produced

Given that the molar mass of water is 18 g/mol, and 2 moles of water are produced, the total mass of water can be calculated as follows:\[ 2 \text{ moles} \times 18 \mathrm{~g/mol} = 36 \mathrm{~g} \text{ of water} \]

Step 4: Final Result

Therefore, the amount of water produced when 1 mole of rhombic sulfur is oxidized by concentrated nitric acid is 36 grams.

Key Concepts

Oxidation State

Understanding oxidation states is essential for predicting the behavior of elements during chemical reactions. An oxidation state, also known as oxidation number, indicates the number of electrons an atom loses, gains, or shares when it forms compounds. In a chemical reaction, we track these changes to understand which elements undergo oxidation and which are reduced. In the oxidation of sulfur ( S ) by nitric acid ( HNO_3 ), sulfur reaches its highest oxidation state of +6, forming sulfuric acid ( H_2SO_4 ).

• When sulfur is oxidized to sulfuric acid, its oxidation state increases from 0 to +6.
• This transformation involves the sulfur atom transferring electrons to oxygen atoms, leading to the formation of sulfuric acid.

Understanding these changes helps us predict product formation and stoichiometry in reactions.

Sulfur

Sulfur is a versatile non-metallic element that plays a critical role in various oxidation-reduction reactions. It can exhibit multiple oxidation states ranging from -2 to +6, which allows it to participate in diverse chemical processes. In the given exercise, sulfur starts as a rhombic sulfur, which is a stable, crystalline form. During its oxidation:

• Sulfur is transformed from its elemental state to its highest oxidation form in sulfuric acid.
• The versatility of sulfur's oxidation states enables it to form a wide array of compounds, such as sulfides, sulfites, and sulfates.

This property makes sulfur crucial in industrial applications and biochemical processes, such as in the manufacture of fertilizers and in the acid rain cycle.

Chemical Equation Balancing

Balancing chemical equations is a fundamental skill in chemistry that ensures the conservation of mass and atoms throughout a reaction. Every equation must reflect that the number of atoms of each element is the same on both sides of the reaction. In the oxidation of sulfur by nitric acid:

• The balanced equation is: \( S + 6 ext{ HNO}_3 \rightarrow H_2 ext{SO}_4 + 6 ext{ NO}_2 + 2 ext{ H}_2 ext{O} \).
• This equation shows that for every mole of sulfur, six moles of nitric acid react to form one mole of sulfuric acid, six moles of nitrogen dioxide, and two moles of water.

Balancing involves adjusting coefficients, ensuring that both sides have equal numbers of each type of atom, which is crucial for accurate reaction predictions and calculations.

Mole Concept

The mole is a fundamental concept in chemistry that relates to quantities of atoms and molecules. It provides a bridge between the atomic scale and the macroscopic world we can measure. In this exercise, the mole concept is used to determine how much water is produced from the reaction:

• 1 mole of sulfur produces 2 moles of water as the reaction proceeds.
• Given that the molar mass of water is 18 g/mol, multiplying the number of moles of water by its molar mass provides the total mass of water: \( 2 \text{ moles} \times 18 \text{ g/mol} = 36 \text{ g} \).

Understanding the mole concept is essential for translating balanced chemical equations into quantitative predictions about the amounts of products and reactants.