Problem 148 - A Complete Resource Book in Chemistry for JEE Main

Question

Among \(\mathrm{A} 1_{2} \mathrm{O}_{3}, \mathrm{SiO}_{2}, \mathrm{P}_{2} \mathrm{O}_{3}\) and \(\mathrm{SO}_{2}\) the correct order of acidic strength is (a) \(\mathrm{Al}_{2} \mathrm{O}_{3}<\mathrm{SiO}_{2}<\mathrm{P}_{2} \mathrm{O}_{3}<\mathrm{SO}_{2}\) (b) \(\mathrm{SO}_{2}<\mathrm{P}_{2} \mathrm{O}_{3}<\mathrm{SiO}_{2}<\mathrm{Al}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{SiO}_{2}<\mathrm{SO}_{2}<\mathrm{Al}_{2} \mathrm{O}_{3}<\mathrm{P}_{2} \mathrm{O}_{3}\) (d) \(\mathrm{Al}, \mathrm{O}_{3}<\mathrm{SiO},<\mathrm{SO},<\mathrm{P}_{3} \mathrm{O}\)

Step-by-Step Solution

Answer

The correct order of acidic strength is option (a).

Step 1: Understanding Acidic Oxide

First, understand that acidic oxides are typically formed by nonmetals and become more acidic moving from left to right across a period in the periodic table. Acidic oxides react with water to form acids.

Step 2: Analyze the Given Oxides

Look at the given oxides: \( \mathrm{Al}_2 \mathrm{O}_3 \), \( \mathrm{SiO}_2 \), \( \mathrm{P}_2 \mathrm{O}_3 \), and \( \mathrm{SO}_2 \). Aluminum oxide is amphoteric but generally less acidic compared to non-metal oxides. Silicon dioxide is a weakly acidic oxide. Phosphorus and sulfur oxides tend to exhibit stronger acidic properties.

Step 3: Determine the Acidic Strength Order

Determine the likely acidic strength order: Aluminum being amphoteric shows lesser acidic strength, followed by silicon, which is weakly acidic. Phosphorus oxide is more acidic than silicon oxide but less than sulfur, which is known for its strong acidic characteristics.

Step 4: Match Options to Determine Correct Order

Based on the analysis, match the probable order of acidic strength \( \mathrm{Al}_2 \mathrm{O}_3 < \mathrm{SiO}_2 < \mathrm{P}_2 \mathrm{O}_3 < \mathrm{SO}_2 \) with the options presented.

Key Concepts

Understanding Acidic Oxides

Acidic oxides are oxides that can react with water to form acids. These oxides are typically formed by non-metals, such as sulfur and phosphorus. As you move across a period in the periodic table from left to right, the elements generally become more electronegative. This means they hold onto their electrons more tightly and are more likely to form oxides that are acidic.
Acidic oxides play a significant role in various chemical reactions and environmental processes. For instance:

• They can dissolve in water to form acids. For example, \[ \text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3 \]
• These reactions often contribute to environmental phenomena like acid rain.

By understanding the nature and behavior of acidic oxides, one can predict their reactions and applications in different chemical contexts.

Periodic Table Trends and Acidic Strength

Trends in the periodic table are essential for understanding the chemical properties of elements, including their acidic or basic nature. As you move from left to right across a period, elements typically transition from metallic to non-metallic character. This transition corresponds with an increase in acidity of the oxides they form. Metals on the left side often form basic oxides, while non-metals on the right generally form acidic oxides.
Deeper into the periodic table:

• Basic oxides, often formed by metals, react with acids.
• Amphoteric oxides can behave as either acids or bases depending on the reaction conditions.
• Acidic oxides readily form acids upon reaction with water.

These trends are used to predict the behavior of elements and their compounds in reactions. Knowing which type of oxide an element will form can inform choices in chemical synthesis and environmental science.

Amphoteric Oxides

Amphoteric oxides are unique types of oxides that can react both as acids and bases. This dual behavior allows them to engage in a wider array of chemical reactions. Aluminum oxide (\(\text{Al}_2\text{O}_3\)) is a classic example, showcasing this amphoteric nature.
In chemical processes:

• It can react with acids. For example, \[ \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \]
• It can also react with bases, such as:\[ \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \]

This ability to react as an acid or a base makes amphoteric oxides particularly versatile in industrial applications and chemical synthesis. Understanding these reactions helps in grasping the full potential and uses of amphoteric compounds.