Problem 10 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following oxides is most basic? (a) \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{SeO}_{2}\) (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (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: Understand Basic and Acidic Oxides

Oxides are either basic or acidic based on their ability to form hydroxide or acids when dissolved in water. Metal oxides, especially those of highly electropositive metals, tend to be basic. The higher the metal's position in the periodic table, the more basic the oxide.

Step 2: Identify the Types of Oxides

List the types of elements in the given compounds: (a) Bismuth (Bi) - a metal. (b) Selenium (Se) - a non-metal. (c) Aluminum (Al) - a metal. (d) Antimony (Sb) - a metalloid.

Step 3: Analyze the Metal Oxides

Compare \((\mathrm{Bi}_{2} \mathrm{O}_{3})\), \((\mathrm{Al}_{2} \mathrm{O}_{3})\), and \((\mathrm{Sb}_{2} \mathrm{O}_{3})\). These oxides range from basic to amphoteric. Metal oxides are generally more basic than non-metal or metalloid oxides.

Step 4: Determine the Most Basic Oxide

The order of basicity for the metal oxides presented is determined by the elements' position within the metal group category. \((\mathrm{Bi}_{2} \mathrm{O}_{3})\) is more basic than \((\mathrm{Al}_{2} \mathrm{O}_{3})\) and \((\mathrm{Sb}_{2} \mathrm{O}_{3})\) due to bismuth being more electropositive than aluminum and antimony.

Key Concepts

Electropositivity

Electropositivity is an important concept in chemistry, particularly when discussing elements and their oxides. Electropositivity refers to the tendency of an element, primarily metals, to release electrons and form positive ions. This tendency affects the basic nature of metal oxides.

When a metal is electropositive, it readily loses electrons to form cations. This makes its oxides more basic. Basic oxides react with water to form hydroxides. For example, when extremely electropositive metals like sodium or potassium form oxides, they react vigorously with water.

• Electropositive elements like bismuth and aluminum tend to form basic oxides.
• The more electropositive the metal, the stronger its oxide's basicity.
• Comparing the oxides of different metals helps determine their basic nature based on electropositivity.

Understanding electropositivity allows us to predict the behavior of metal oxides, such as Bi₂O₃, Al₂O₃, and Sb₂O₃, where bismuth's electropositivity makes Bi₂O₃ more basic than the others.

Metal Oxides

Metal oxides are compounds formed between metals and oxygen. They range widely in their chemical properties. The basicity or acidity of a metal oxide largely depends on its metal's characteristics, including electropositivity.

In the case of the exercise oxides, Bi₂O₃, Al₂O₃, and Sb₂O₃, they demonstrate different degrees of basicity to amphoterism due to their metal nature. Metal oxides react with water to produce hydroxides, which makes them basic.

• Bi₂O₃: Oxides of more electropositive metals, like bismuth, are typically more basic.
• Al₂O₃: Known as being amphoteric; it can act as both acidic and basic, depending on the environment.
• Sb₂O₃: Lies between metals and non-metals, making it less basic or more amphoteric.

These oxides showcase the diversity among metal oxides, ranging from strong basicity to potentially dual chemical behavior. Recognizing these variations helps in predicting their chemical reactivity.

Periodic Table Trends

The periodic table is a powerful tool in understanding the properties of elements, including their oxides. Moving across and down the table, specific trends become apparent, particularly in relation to electropositivity and oxide properties.

As we move down a group in the periodic table, electropositivity of elements generally increases. This trend correlates with the increase in metallic character and, correspondingly, more basic oxides.

• Elements on the bottom left are typically more electropositive, having metal oxides that are more basic.
• Across a period, metals often become less electropositive leading to less basic behavior.
• Comparing the periodic table positions helps visualize why Bi₂O₃ is more basic than Al₂O₃ or Sb₂O₃.

These periodic trends are key to predicting and understanding the variations in oxides' properties. With these trends in mind, it becomes easier to determine why certain metal oxides behave more basic than others based on their position in the periodic table.