Problem 112 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following oxides is/are amphoteric? 1\. \(\mathrm{Na}_{2} \mathrm{O}\) 2\. \(\mathrm{CaO}\) \(3 . \mathrm{Al}_{2} \mathrm{O}_{3}\) 4\. \(\mathrm{SnO}_{2}\) (a) \(2,3,4\) (b) 3,4 (c) 2,3 (d) 1,4

Step-by-Step Solution

Answer

The amphoteric oxides are \(\mathrm{Al}_2\mathrm{O}_3\) and \(\mathrm{SnO}_2\), answer is (b) 3,4.

Step 1: Understand the Concept of Amphoteric Oxides

Amphoteric oxides are those oxides that can react with both acids and bases to form salt and water. They have both acidic and basic properties.

Step 2: Analyze 4 Na_2O\)

\(\mathrm{Na}_2\mathrm{O}\) is a basic oxide, as it reacts with water to form \(\mathrm{NaOH}\), a strong base. It does not show amphoteric characteristics.

Step 3: Analyze \mathrm{CaO}\)

\(\mathrm{CaO}\) is a metal oxide that reacts with water to form \(\mathrm{Ca(OH)}_2\), a basic solution. It does not react with acids and bases in amphoteric manner, so it is just a basic oxide.

Step 4: Analyze \(\mathrm{Al}_2\mathrm{O}_3\)

\(\mathrm{Al}_2\mathrm{O}_3\) is known to react with acids, forming salts, as well as with bases, like \(\mathrm{NaOH}\), to form aluminates. Therefore, it is an amphoteric oxide.

Step 5: Analyze \(\mathrm{SnO}_2\)

\(\mathrm{SnO}_2\) can react with both acids and bases. It reacts with acids to form tin salts and with strong bases like \(\mathrm{NaOH}\) to form stannate. Thus, it is an amphoteric oxide.

Step 6: Identify the Correct Answer Based on Analysis

From the analysis, \(\mathrm{Al}_2\mathrm{O}_3\) and \(\mathrm{SnO}_2\) are amphoteric. This corresponds with option (b) \(3,4\).

Key Concepts

Properties of Oxides

Oxides are compounds made up of oxygen and another element. They can be broadly classified based on their chemical properties into acidic, basic, and amphoteric oxides. Let's take a closer look at each:

• **Acidic Oxides:** These oxides, generally non-metal oxides, react with water to form acids. For instance, carbon dioxide (\( \mathrm{CO}_2 \)) dissolves in water to form carbonic acid (\( \mathrm{H}_2\mathrm{CO}_3 \)).
• **Basic Oxides:** Typically formed by metals, these react with water to produce a basic solution. For example, calcium oxide (\( \mathrm{CaO} \)) reacts with water to form calcium hydroxide (\( \mathrm{Ca(OH)}_2 \)).
• **Amphoteric Oxides:** These unique oxides can react with both acids and bases, showing dual properties. Examples include aluminum oxide (\( \mathrm{Al}_2\mathrm{O}_3 \)) and tin(IV) oxide (\( \mathrm{SnO}_2 \)).

This classification helps in predicting their reactions and behavior in chemical processes.
Understanding the properties of these oxides is essential for studying their reactions and applications.

Reactions with Acids and Bases

Oxides exhibit fascinating reactions when they come into contact with acids and bases. This reactivity is crucial for determining their classification and behavior:
For **basic oxides**, such as \( \mathrm{Na}_2\mathrm{O} \), the reaction with acids leads to the formation of salt and water. However, they usually do not react with other bases. Basic oxides like calcium oxide (\( \mathrm{CaO} \)) form hydroxides when dissolved in water, providing basic characteristics.
**Acidic oxides** react well with bases. For example, sulfur dioxide (\( \mathrm{SO}_2 \)) reacts with sodium hydroxide (\( \mathrm{NaOH} \)) to produce sodium sulfite (\( \mathrm{Na_2SO_3} \)).
The true versatility lies with **amphoteric oxides**. Amphoteric oxides like \( \mathrm{Al}_2\mathrm{O}_3 \) and \( \mathrm{SnO}_2 \) can react with both acids and bases:

• With acids, they form salts and water, exhibiting basic behavior. \( \mathrm{Al}_2\mathrm{O}_3 \) reacts with hydrochloric acid (\( \mathrm{HCl} \)) to produce aluminum chloride (\( \mathrm{AlCl}_3 \)).
• When reacting with bases, they behave like acids. \( \mathrm{Al}_2\mathrm{O}_3 \) can dissolve in \( \mathrm{NaOH} \) to form sodium aluminate (\( \mathrm{NaAlO}_2 \)).

Through these interactions, amphoteric oxides demonstrate their dual nature, showcasing the variety of reactions in chemistry.

Identifying Amphoteric Substances

Identifying whether an oxide is amphoteric involves observing its reactions with acids and bases. Amphoteric substances showcase dual characteristics, resulting in unique interactions.
To investigate if an oxide is amphoteric, one should look at:

• **Reaction with Acids:** Check if the oxide reacts with acidic solutions to produce a salt. If it forms a salt when reacting with an acid, it may possess basic properties.
• **Reaction with Bases:** Determine if the oxide reacts with bases to yield a different salt or complex. For example, an oxide that reacts to dissolve in a strong base often indicates an amphoteric nature.

Examining specific reactions helps in identifying amphoteric behavior. For example, testing aluminum oxide (\( \mathrm{Al}_2\mathrm{O}_3 \)) will reveal that it can form aluminum chloride with \( \mathrm{HCl} \) and dissolve in \( \mathrm{NaOH} \).
The key is in noting how well these oxides manage to interact with both types of substances. These observations offer insights into their dual ability, as seen in substances like \( \mathrm{SnO}_2 \) and \( \mathrm{Al}_2\mathrm{O}_3 \). This broad understanding helps in identifying such substances in various chemical contexts.