Problem 52 - A Complete Resource Book in Chemistry for JEE Main

Question

A pair of amophoteric oxides from the following is (a) \(\mathrm{VO}_{2}\) and \(\mathrm{CrO}\) (b) \(\mathrm{VO}_{2}\) and \(\mathrm{CrO}_{3}\) (c) \(\mathrm{VO}\) and \(\mathrm{V}_{2} \mathrm{O}_{5}\) (d) \(\mathrm{VO}_{2}\) and \(\mathrm{Cr}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

Option (d) \( \mathrm{VO}_{2} \) and \( \mathrm{Cr}_{2} \mathrm{O}_{3} \) are amphoteric oxides.

Step 1: Understand Amphoteric Oxides

Amphoteric oxides are oxides that can react both with acids and bases to form salts and water. Our task is to identify which given pair includes oxides that demonstrate this dual behavior.

Step 2: Analyze Each Option

Let's examine the amphoteric nature of each oxide pair:- (a) \( \mathrm{VO}_{2} \) and \( \mathrm{CrO} \) - \( \mathrm{CrO} \) is not amphoteric, but \( \mathrm{VO}_{2} \) is amphoteric.- (b) \( \mathrm{VO}_{2} \) and \( \mathrm{CrO}_{3} \) - Neither is amphoteric as \( \mathrm{CrO}_{3} \) is acidic.- (c) \( \mathrm{VO} \) and \( \mathrm{V}_{2} \mathrm{O}_{5} \) - Neither are amphoteric, both are acidic.- (d) \( \mathrm{VO}_{2} \) and \( \mathrm{Cr}_{2} \mathrm{O}_{3} \) - Both are amphoteric oxides.

Step 3: Select the Correct Answer

From Step 2, we found that option (d), which includes \( \mathrm{VO}_{2} \) and \( \mathrm{Cr}_{2} \mathrm{O}_{3} \), contains two amphoteric oxides. Therefore, (d) is the correct answer.

Key Concepts

Oxides Reactivity

Oxides are chemical compounds composed of oxygen bonded to another element. Their reactivity is determined by the properties of the metal and the oxidation state of the other element to which oxygen is bound.
Some oxides are highly reactive and can participate in various chemical reactions, such as reacting with acids, bases, or other compounds. Two types of oxide reactivities are commonly discussed: acidic oxides and basic oxides.

• **Acidic oxides** react with bases to form salts and water. Common examples include non-metal oxides such as carbon dioxide and sulfur dioxide.
• **Basic oxides** react with acids to form salts and water. Examples include metal oxides like sodium oxide and calcium oxide.

These reactions are crucial in understanding the reactivity and classification of oxides. Amphoteric oxides, a unique category, react with both acids and bases. This dual nature depends upon the specific metal involved and its oxidation state, which we'll explore further.

Acid-Base Reactions

Acid-base reactions involve the transfer of protons between reactants and are fundamental to many chemical processes. Oxides often participate in these reactions, showcasing different properties based on their nature.
Amphoteric oxides, like both (\( \text{VO}_2 \) and \( \text{Cr}_2\text{O}_3 \)), exhibit a fascinating ability to behave as either acids or bases depending on the conditions.

• When reacted with acids, amphoteric oxides typically form water and a corresponding salt.
• Conversely, when they react with bases, they again form water and a different salt that may involve a complex anion.

This versatility provides insight into their internal structure, which allows them to undergo such varied interactions. Understanding these reactions helps us comprehend how oxides function in different chemical environments, enriching our grasp on topics like buffer solutions and metal corrosion.

Chemistry Problem Solving

Solving chemistry problems involves a step-by-step approach that breaks down complex concepts into manageable pieces, enabling better understanding. Applying this to identify amphoteric oxides involves a few critical steps:

• **Understanding Definitions:** Clearly define what amphoteric compounds are—they must react with both acids and bases.
• **Analyzing Each Option:** Separately examine the given pairs to determine their amphoteric nature using known chemical knowledge.
• **Matching to Known Characteristics:** Compare the identified properties of each oxide with confirmed amphoteric behaviors, such as those of \( \text{VO}_2 \) and \( \text{Cr}_2\text{O}_3 \).

This systematic method fosters clarity, ensuring that even complex molecular interactions become comprehensible. It also highlights the wide application of fundamental principles, such as acidity and basicity, in broader chemistry.

Oxidation States

The oxidation state of an element in a compound describes the degree of oxidation, often representing the number of electrons lost or gained as compared to the neutral atom.
For oxides, this concept can describe oxygen's role in bonding and reactivity. Often, the differing oxidation states of metals lead to variations in oxide properties, such as:

• **Varied Reactivity:** As observed, \( \text{VO}_2 \) has vanadium in a +4 oxidation state, influencing its ability to react amphoterically.
• **Stability:** Metals can exist in various oxidation states within different oxides, each potentially unique in its stability and reactivity characteristics.

Recognizing these states is crucial when analyzing the chemical behavior of oxides, especially amphoteric ones, as these states help predict and explain their acid-base behavior and their role in redox reactions.