Problem 78 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Arrange the following oxides in the decreasing order of Bronsted basicity: \(\mathrm{BaO}, \mathrm{SO}_{3}, \mathrm{CO}_{2}, \mathrm{Cl}_{2} \mathrm{O}_{7}, \mathrm{~B}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

\(\mathrm{BaO} > \mathrm{B}_2\mathrm{O}_3 > \mathrm{CO}_2 > \mathrm{SO}_3 > \mathrm{Cl}_2\mathrm{O}_7\).

Step 1: Identify Bronsted Basicity

Bronsted basicity refers to the ability of a compound to accept protons (H+). In the context of oxides, a more basic oxide will be capable of forming hydroxide ions (OH-) when reacting with water. Generally, metal oxides are basic, non-metal oxides are acidic, and semimetal oxides can be amphoteric.

Step 2: Classify the Given Oxides

Classify each oxide as a metal oxide or non-metal oxide. \(\mathrm{BaO}\) is a metal oxide. \(\mathrm{SO}_3\), \(\mathrm{CO}_2\), \(\mathrm{Cl}_2\mathrm{O}_7\), and \(\mathrm{B}_2\mathrm{O}_3\) are non-metal oxides.

Step 3: Determine Basic vs Acidic Behavior

Metal oxide \(\mathrm{BaO}\) tends to be basic. Non-metal oxides like \(\mathrm{SO}_3\), \(\mathrm{CO}_2\), \(\mathrm{Cl}_2\mathrm{O}_7\), and \(\mathrm{B}_2\mathrm{O}_3\) tend to be acidic. The order of basicity usually decreases from basic to acidic oxides.

Step 4: Rank the Oxides by Basicity

List the oxides from most basic to least basic (most acidic). Based on basicity: \(\mathrm{BaO} >\) (most basic), then \(\mathrm{B}_2\mathrm{O}_3\) as it is amphoteric with weak acidic behavior, followed by the acidic oxides \(\mathrm{CO}_2\), \(\mathrm{SO}_3\), and \(\mathrm{Cl}_2\mathrm{O}_7\) (most acidic).

Key Concepts

Basic Oxides

Basic oxides are a type of oxide that exhibit basic properties. These are typically formed from metals reacting with oxygen. When dissolved in water, basic oxides produce hydroxide ions (OH^-), which is a signature of their basic nature. These ions can result in a basic (or alkaline) solution. For example, when barium oxide (BaO), a typical metal oxide, is added to water, it forms barium hydroxide:
\[ \text{BaO} + \text{H}_2\text{O} \rightarrow \text{Ba(OH)}_2 \]
Basic oxides are often used in various applications, including agriculture and industry, due to their reactive properties.

• They are commonly found in Group 1 and Group 2 elements of the periodic table, like Na and Ca.
• Basic oxides tend to form strong bases when dissolved in water.
• Their basic strength can be influenced by the metal's position on the periodic table; typically, oxides from the left side are more basic.

Acidic Oxides

Acidic oxides are oxides that display acidic characteristics and are generally formed by the reaction of nonmetals with oxygen. These compounds can form acids when they react with water. For example, sulfur trioxide (SO_3), a non-metal oxide, reacts with water to form sulfuric acid:
\[ \text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 \]
This tendency to form acids is what gives these oxides their acidic nature. Here are some additional points about acidic oxides:

• They can react with bases in neutralization reactions to yield salt and water.
• Common acidic oxides include CO_2, SO_2, and N_2O_5.
• These oxides do not conduct electricity unless dissolved in water.

Amphoteric Oxides

Amphoteric oxides are unique because they can exhibit properties of both acidic and basic oxides, meaning they can react with both acids and bases. A good example of this kind of oxide is aluminum oxide (Al_2O_3), which can act as an acid in the presence of a base and as a base in the presence of an acid. For instance:

• With a strong acid: \[ \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \]
• With a strong base: \[ \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \]

Amphoteric behavior is notable in elements that are situated on the periodic table border between metals and nonmetals.
Here are a few characteristics of amphoteric oxides:

• They are usually formed from elements that lie near the metalloid line.
• These oxides can compromise both acidic and basic properties by forming salts.
• Amphoteric oxides can act as buffers, stabilizing pH by reacting with both excess acids and bases in solutions.