Problem 15 - A Complete Resource Book in Chemistry for JEE Main

Question

The most acidic oxide is (a) \(\mathrm{MgO}\) (b) \(\mathrm{CaO}\) (c) \(\mathrm{Na}_{2} \mathrm{O}\) (d) \(\mathrm{Al}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

(d) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is the most acidic oxide.

Step 1: Understand Acidic Oxides

Acidic oxides are oxides that can form acids when combined with water, and react with bases to form water and a salt. Typically, these are oxides of nonmetals or elements with high electronegativity.

Step 2: Analyze the Given Oxides

Review the provided options: (a) \(\mathrm{MgO}\), (b) \(\mathrm{CaO}\), (c) \(\mathrm{Na}_{2} \mathrm{O}\), (d) \(\mathrm{Al}_{2} \mathrm{O}_{3}\). To determine which is most acidic, consider the metal involved and its position in the periodic table.

Step 3: Classify Each Oxide

\(\mathrm{MgO}\), \(\mathrm{CaO}\), and \(\mathrm{Na}_2\mathrm{O}\) are all oxides of metals found on the left side of the periodic table. They are basic oxides. \(\mathrm{Al}_{2} \mathrm{O}_{3}\), however, is an amphoteric oxide, meaning it can react both as an acid and a base, but in this context, it is the only one capable of showing acidic behavior.

Step 4: Identify the Most Acidic Oxide

Since \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is the only element capable of exhibiting acidic characteristics among the choices, it is the most acidic oxide. The other options are basic oxides.

Key Concepts

Understanding the Periodic Table

The periodic table is a systematic arrangement of elements, showcasing the periodic law that properties of elements recur periodically when they are arranged by atomic number. It is divided into periods (rows) and groups (columns). The position of an element in the periodic table reveals much about its chemical properties.

• Elements on the left side, mainly metals, often form basic oxides.
• Nonmetals, found on the right, usually form acidic oxides.
• In the middle, where transition and post-transition metals are, you'll find amphoteric oxides, which can behave as both acids and bases.

The periodic table helps predict whether an oxide will be basic, acidic, or amphoteric based on the element's position.

Properties of Basic Oxides

Basic oxides are formed by metals and are usually ionic in nature. They readily react with water to form hydroxides, which are alkaline. When they react with acids, they produce water and a salt.

• For example, \(\mathrm{MgO}\) reacts with water to form \(\mathrm{Mg(OH)_2}\).
• Similarly, \(\mathrm{CaO}\) forms \(\mathrm{Ca(OH)_2}\) with water.

These reactions are characteristic of basic oxides:

• They neutralize acids, thus losing their basicity.
• Examples include oxides of Group 1 and Group 2 elements in the periodic table, like sodium and calcium oxides.

Understanding these properties helps in determining the behavior of the oxides in various reactions.

Exploring Amphoteric Oxides

Amphoteric oxides are unique because they can react with both acids and bases. This dual behavior makes them versatile. An example is \(\mathrm{Al_2O_3}\):

• It reacts with acids like \(\mathrm{HCl}\) to form \(\mathrm{AlCl_3}\) and water.
• With bases like \(\mathrm{NaOH}\), it forms sodium aluminate \(\mathrm{NaAlO_2}\).

These reactions display its ability to serve as either an acid or a base depending on the reactant.

• Amphoteric oxides are generally formed by elements found in the middle of the periodic table, like aluminum and zinc.
• They are integral in industrial and laboratory applications, where tailored reactions are required.

This amphoteric nature is crucial in fields such as material science and catalysis.