Problem 146 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following is an amphoteric oxide? (a) \(\mathrm{ZnO}\) (b) \(\mathrm{Na}_{2} \mathrm{O}\) (c) \(\mathrm{SO}_{2}\) (d) \(\mathrm{B}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

The amphoteric oxide is \(\mathrm{ZnO}\).

Step 1: Identify Amphoteric Oxides

An amphoteric oxide can react with both acids and bases to form salts and water. Recognizing that zinc oxide (ZnO7) is a common example of an amphoteric oxide helps identify the correct answer.

Step 2: Evaluate Other Options

Examine the other options: - Na_2O7 is a basic oxide, as it reacts with water to give a base (NaOH7). - SO_27 is an acidic oxide, as it reacts with water to form sulfurous acid. - B_2O_37 is also an acidic oxide, forming boric acid in reactions.

Key Concepts

Zinc Oxide

Zinc oxide (ZnO) is an interesting compound due to its amphoteric nature. What this means is that it can react both as an acid and as a base, depending on its environment. For example, when ZnO interacts with a strong acid like hydrochloric acid (HCl), it behaves as a base, forming zinc chloride (ZnCl₂) and water. On the other hand, when exposed to a base like sodium hydroxide (NaOH), it acts as an acid, resulting in a zincate ion \[ \mathrm{Na_2[Zn(OH)_4]} \]. This dual reactivity is what classifies it as an amphoteric oxide.
This property is not unique to zinc oxide, but ZnO is one of the most common examples studied in chemistry. Amphoteric oxides play significant roles in various chemical applications, including catalysis and material science.

Acidic Oxides

Acidic oxides are non-metal oxides that react with water to form acidic solutions. These compounds typically arise from non-metals, like carbon or sulfur. For instance, sulfur dioxide (SO₂) is a well-known acidic oxide. When SO₂ is dissolved in water, it forms sulfurous acid \( \mathrm{H_2SO_3} \).

• They usually exhibit lower reactivity compared to basic oxides.
• They are prevalent in industrial processes and can contribute to environmental issues like acid rain.

In the exercise, SO₂ and B₂O₃ are given as examples of acidic oxides. B₂O₃ forms boric acid when combined with water. Understanding the behavior of acidic oxides is important in environmental chemistry and industrial applications.

Basic Oxides

Basic oxides are compounds that react with acids to form salt and water, and are typically formed from metal elements. One common example is sodium oxide (Na₂O), which readily reacts with water to produce sodium hydroxide (NaOH), a strong base.

• They are often formed through the oxidation of metals.
• Basic oxides play a crucial role in various chemical and industrial processes.

In the context of the original exercise, Na₂O is identified as a basic oxide. Knowledge of basic oxides and their reactions can help in understanding and predicting the outcomes of many chemical reactions.

Chemical Reactions with Acids and Bases

Understanding the interactions between oxides and acids or bases is crucial in grasping their role in chemistry.
When oxides react with acids or bases, the typical products of these reactions are salts and water. Amphoteric oxides like zinc oxide can form different products depending on whether they are reacting with an acid or a base. For example:

• Reaction with an Acid: \( \mathrm{ZnO + 2HCl \rightarrow ZnCl_2 + H_2O} \)
• Reaction with a Base: \( \mathrm{ZnO + 2NaOH + H_2O \rightarrow Na_2[Zn(OH)_4]} \)

This dual reactivity is important for many industrial processes, such as refining metals or forming polymer additives. By understanding these reactions, chemists can better predict how different substances will react and be used in practical applications.