Problem 12 - Chemistry and Chemical Reactivity

Question

Place the following oxides in order of increasing basicity: \(\mathrm{Na}_{2} \mathrm{O}, \mathrm{Al}_{2} \mathrm{O}_{3}, \mathrm{SiO}_{2}, \mathrm{SO}_{3}\).

Step-by-Step Solution

Answer

Order of increasing basicity: \(\mathrm{SO}_3, \mathrm{SiO}_2, \mathrm{Al}_2\mathrm{O}_3, \mathrm{Na}_2\mathrm{O}\).

Step 1: Understand Basicity in Oxides

Basicity in oxides generally refers to the ability of the oxide to react with acids to form salts and water. Basic oxides usually form from metals, while acidic oxides tend to form from non-metals.

Step 2: Identify Types of Oxides

Determine if each oxide is basic, acidic, or amphoteric. \(\mathrm{Na}_2\mathrm{O}\) is a basic oxide, \(\mathrm{Al}_2\mathrm{O}_3\) is amphoteric, \(\mathrm{SiO}_2\) is acidic, and \(\mathrm{SO}_3\) is acidic.

Step 3: Arrange Oxides by Basicity

Place the oxides in order of increasing basicity. Since \(\mathrm{SiO}_2\) and \(\mathrm{SO}_3\) are both acidic, they should be first. \(\mathrm{Al}_2\mathrm{O}_3\) is amphoteric, having some basic characteristics but less than \(\mathrm{Na}_2\mathrm{O}\), which is fully basic.

Key Concepts

Acidic Oxides

Acidic oxides are oxides that can react with water to form acids or with bases to form salts. These oxides are typically formed from nonmetals. When they dissolve in water, they contribute to the acidity of the solution. For example, sulfur trioxide (\(\mathrm{SO}_3\)), a non-metal oxide, reacts with water to form sulfuric acid (\(\mathrm{H}_2\mathrm{SO}_4\)). Another example is silicon dioxide (\(\mathrm{SiO}_2\)), which, although not reacting readily with water, can still react with strong bases to form silicates. Such properties define these oxides as acidic.

• Non-metal oxides: Typically show acidic properties.
• Reactions: Form acids when combined with water or form salts when reacting with bases.
• Examples: \(\mathrm{SO}_3\) and \(\mathrm{SiO}_2\).

Understanding the nature of acidic oxides helps in predicting their reactions and their role in chemical processes.

Amphoteric Oxides

Amphoteric oxides are unique as they exhibit both acidic and basic properties. This dual nature allows them to react with both acids and bases to form salts. A classic example is aluminum oxide (\(\mathrm{Al}_2\mathrm{O}_3\)), which can react with hydrochloric acid (\(\mathrm{HCl}\)) to form aluminum chloride (\(\mathrm{AlCl}_3\)) and with sodium hydroxide (\(\mathrm{NaOH}\)) to form sodium aluminate (\(\mathrm{NaAlO}_2\)).

• Dual Reactivity: Reacts with both acids and bases.
• Salts Formation: Produces different types of salts depending on the reactant.
• Example: \(\mathrm{Al}_2\mathrm{O}_3\) is a typical amphoteric oxide.

This dual characteristic is important in industrial processes where balance between acids and bases may be necessary.

Metal vs Non-metal Oxides

Oxides can be categorized based on the element they originate from—metals or non-metals. Metal oxides typically have basic characteristics, whereas non-metal oxides are mostly acidic. Metal oxides, such as sodium oxide (\(\mathrm{Na}_2\mathrm{O}\)), react with water to form hydroxides which are basic in nature.

• Metal Oxides: Often basic, metal oxides form hydroxides.
• Non-metal Oxides: Usually acidic, they react with water to form acids.

Understanding whether an element forms a metal or non-metal oxide helps predict its behavior in chemical reactions. This distinction clarifies the order of basicity: metals generally increase basicity, while non-metals tend towards acidity.