Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is produced when magnesium reacts with hot concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4} ?\) (a) \(\mathrm{H}_{2}\) (b) \(\mathrm{S}\) (c) \(\mathrm{MgO}\) (d) \(\mathrm{SO}_{2}\)

Step-by-Step Solution

Answer

Sulfur dioxide, \(\mathrm{SO}_{2}\), is produced.

Step 1: Understand the Reaction

When magnesium reacts with hot concentrated sulfuric acid (\(\mathrm{H}_{2}\mathrm{SO}_{4}\)), it does not behave like typical acid-metal reactions that produce hydrogen gas. Instead, due to the concentration and temperature of the acid, sulfur dioxide is produced.

Step 2: Write the Balanced Chemical Equation

The balanced chemical equation for the reaction between magnesium and hot concentrated sulfuric acid is:\[\mathrm{Mg} + 2\mathrm{H}_{2}\mathrm{SO}_{4} \rightarrow \mathrm{MgSO}_{4} + 2\mathrm{H}_{2}\mathrm{O} + \mathrm{SO}_{2}\]This shows that sulfur dioxide (\(\mathrm{SO}_{2}\)) is one of the products.

Step 3: Identify the Resulting Product

From the balanced chemical equation, it is evident that the product formed is primarily magnesium sulfate, water, and sulfur dioxide. Among the answer choices given, (d) \(\mathrm{SO}_{2}\) is present in the equation, confirming it as the correct answer.

Key Concepts

Balanced Chemical Equation

To fully understand chemical reactions, one must know how to balance chemical equations properly. A balanced equation maintains the conservation of mass, meaning the number of atoms of each element is the same on both sides of the equation. When magnesium reacts with sulfuric acid, the balanced equation is:\[\mathrm{Mg} + 2\mathrm{H}_{2}\mathrm{SO}_{4} \rightarrow \mathrm{MgSO}_{4} + 2\mathrm{H}_{2}\mathrm{O} + \mathrm{SO}_{2}\]

• On the left, we have 1 magnesium (Mg), 4 hydrogens (H), 2 sulfur (S), and 8 oxygen (O) atoms.
• On the right, we also have 1 magnesium, 4 hydrogens, 2 sulfurs, and 8 oxygens.

By following these steps, we confirm that the chemical equation is balanced. This ensures that we understand the proportions of reactants and products involved in the reaction, which is essential for predicting outcomes and yields in chemical processes.

Acid-Metal Reactions

Acid-metal reactions typically involve the metal displacing hydrogen from the acid, resulting in hydrogen gas (\(\mathrm{H}_{2}\)) being released. For example, when zinc reacts with hydrochloric acid, zinc chloride and hydrogen gas are typically produced:\[\mathrm{Zn} + 2\mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2} + \mathrm{H}_{2}\]
However, the reaction between magnesium and hot concentrated sulfuric acid (\(\mathrm{H}_{2}\mathrm{SO}_{4}\)) is a bit different.

• Due to the high concentration and temperature, the typical production of hydrogen gas is replaced by the production of sulfur dioxide (\( \mathrm{SO}_{2} \)).
• The equation for this reaction reflects these unique conditions.

Understanding these nuances helps in predicting the correct products and manipulating conditions to obtain desired chemical outcomes.

Sulfur Dioxide Production

Sulfur dioxide (\(\mathrm{SO}_{2}\)) is a significant product of certain acid-metal reactions, especially under specific conditions like high concentration and temperature. In the reaction between magnesium and hot concentrated sulfuric acid:

• Sulfur dioxide is produced instead of hydrogen gas due to the oxidizing nature of concentrated \(\mathrm{H}_{2}\mathrm{SO}_{4}\)
• This reaction produces \(\mathrm{SO}_{2}\) along with magnesium sulfate (\(\mathrm{MgSO}_{4}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)).

Sulfur dioxide itself is an important compound, often used in industry for its bleaching, disinfecting, and reducing properties.
Moreover, it also acts as a precursor to sulfuric acid in an industrial setting, demonstrating its versatility and importance in chemical manufacturing.