Problem 43 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is the most basic oxide? (a) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{SeO}_{2}\) (c) \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) (d) \(\mathrm{Sb}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

The most basic oxide is \(\mathrm{Bi}_{2} \mathrm{O}_{3}\).

Step 1: Understanding Basic Oxides

Basic oxides are oxides that react with acids to form salt and water and are usually formed by metals. They generally belong to the left side of the periodic table.

Step 2: Analyze Given Oxides

Analyze the chemical nature of each oxide: (a) \( \mathrm{Al}_{2} \mathrm{O}_{3} \) is amphoteric and is not dominantly basic because it shows both acidic and basic properties. (b) \( \mathrm{SeO}_{2} \) is acidic as Selenium is a non-metal.(c) \( \mathrm{Bi}_{2} \mathrm{O}_{3} \) is basic due to its metallic nature. (d) \( \mathrm{Sb}_{2} \mathrm{O}_{3} \) is amphoteric, having both acidic and basic properties.

Step 3: Identify the Most Basic

From our analysis, \( \mathrm{Bi}_{2} \mathrm{O}_{3} \) shows basic properties because Bismuth is a post-transition metal which tends to form basic oxides, making it the most basic oxide among the given options.

Key Concepts

Amphoteric Oxides

Amphoteric oxides are fascinating because they display both acidic and basic characteristics. This dual nature allows them to react with both acids and bases to form salts and water. Not every oxide has amphoteric properties; typical examples include alumina (\( \mathrm{Al}_2\mathrm{O}_3 \)) and antimony trioxide (\( \mathrm{Sb}_2\mathrm{O}_3 \)).

• **Acidic Reactions**: When these oxides react with acids, they behave as bases. For instance, when aluminum oxide reacts with hydrochloric acid, it produces aluminum chloride and water.
• **Basic Reactions**: Conversely, when they react with strong bases like sodium hydroxide, they act as acids, forming compounds like sodium aluminate.

This property ties closely to the nature of the element forming the oxide. Elements positioned near the metalloid line in the periodic table often yield amphoteric oxides. This positioning facilitates the blend between metallic and non-metallic behavior, enabling them to exhibit versatile chemical reactivity.

Metallic Nature

The concept of metallic nature is central to understanding the behavior of basic oxides. Metals, characterized by their shiny appearance, malleability, and good conductivity, tend to form oxides with distinct basic properties. This is primarily due to their inclination to donate electrons during chemical reactions.

• **Electron Donation**: Metal atoms have fewer electrons in their outer shell, which they easily lose, making them great electron donors in reactions.
• **Basic Oxide Formation**: When metals react with oxygen, metal oxides are formed, which are generally basic. These oxides tend to react with acids to neutralize them, forming salts and water.

Basic oxides are common among the alkali metals and alkaline earth metals, found on the left side of the periodic table. Post-transition metals like bismuth also maintain this metallic character, contributing to the basic nature of their oxides. Understanding metallic nature is key to predicting how these substances will behave in various chemical situations.

Periodic Table Trends

Periodic table trends help explain why certain elements exhibit specific chemical properties, including the tendencies of their oxides. These trends are patterns seen across periods (rows) and groups (columns) of the periodic table and are vital for predicting the behavior of elements.

• **Metallic Character**: As you move from right to left across a period and from top to bottom within a group, the elements become more metallic. Increased metallic nature often means the elements are more likely to form basic oxides.
• **Electronegativity**: This property, which decreases from left to right across a period and down a group, impacts how an element forms compounds. Non-metals with high electronegativity tend to form acidic oxides.

Examples: Elements like bismuth and antimony are notable because of their position on the periodic table that allows them to form oxides with varied properties. Recognizing these trends helps in identifying the nature of the oxides, whether they are basic, acidic, or amphoteric, based on their elemental origins.