Question

(a) Classify following oxides as neutral, acidic, basic or amphoteric: \(\mathrm{CO}, \mathrm{B}_{2} \mathrm{O}_{3}, \mathrm{SiO}_{2}, \mathrm{CO}_{2}, \mathrm{Al}_{2} \mathrm{O}_{3}, \mathrm{PbO}_{2}, \mathrm{Tl}_{2} \mathrm{O}_{3}\) (b) Write suitable chemical equations to show their nature.

Short answer

CO is neutral, B₂O₃ and SiO₂ are acidic, CO₂ is acidic, Al₂O₃ and PbO₂ are amphoteric, Tl₂O₃ is basic.

Step-by-step solution

Understand the Types of Oxides

Oxides are chemical compounds consisting of oxygen and another element. They can be classified into four main types: - **Neutral Oxides**: Do not react with acids or bases (e.g., CO). - **Acidic Oxides**: React with bases to form salt and water (e.g., CO₂, SO₂). - **Basic Oxides**: React with acids to form salt and water (e.g., MgO). - **Amphoteric Oxides**: React with both acids and bases (e.g., Al₂O₃).

Classify Each Oxide

Identify the type of oxide for each compound: - CO: Neutral oxide, as it does not react typically with acids or bases. - B₂O₃: Acidic oxide, as it reacts with bases. - SiO₂: Acidic oxide, reacts with bases like NaOH. - CO₂: Acidic oxide, reacts with bases (e.g., NaOH). - Al₂O₃: Amphoteric oxide, reacts with both acids (HCl) and bases (NaOH). - PbO₂: Amphoteric oxide, reacts with both acids and bases. - Tl₂O₃: Basic oxide, reacts with acids.

Write Chemical Equations to Show Their Nature

Demonstrate by writing chemical reactions for acidic, basic, and amphoteric oxides:- **CO**: Neutral, no typical reaction.- **B₂O₃**: \[ \text{B}_2\text{O}_3 + 6\text{NaOH} \rightarrow 2\text{Na}_3\text{BO}_3 + 3\text{H}_2\text{O} \]- **SiO₂**: \[ \text{SiO}_2 + 2\text{NaOH} \rightarrow \text{Na}_2\text{SiO}_3 + \text{H}_2\text{O} \]- **CO₂**: \[ \text{CO}_2 + 2\text{NaOH} \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} \]- **Al₂O₃**: \[ \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \] \[ \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \]- **PbO₂**: \[ \text{PbO}_2 + 4\text{HCl} \rightarrow \text{PbCl}_2 + \text{Cl}_2 + 2\text{H}_2\text{O} \] \[ \text{PbO}_2 + 2\text{NaOH} \rightarrow \text{Na}_2\text{PbO}_3 + \text{H}_2\text{O} \]- **Tl₂O₃**: \[ \text{Tl}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{TlCl}_3 + 3\text{H}_2\text{O} \]

Review the Classifications

Verify that each oxide is classified correctly based on their chemical behavior with acids or bases.

Key concepts

Neutral Oxides

Neutral oxides are oxides that do not show a significant chemical reaction with either acids or bases. This makes them quite unique compared to other oxides, as they don't form salts or water during interactions. The reason for this lack of reactivity is usually because of the molecular structure that doesn't allow easy ionization or reaction in aqueous solutions.
Common examples of neutral oxides include carbon monoxide (CO), nitrous oxide (N₂O), and water (H₂O). In the exercise, CO was identified as a neutral oxide because it doesn't typically react with common acids or bases.
Understanding neutral oxides is important because they often appear in discussions about air pollution and greenhouse gases. For instance, carbon monoxide is a common byproduct of incomplete combustion in engines, making its neutral nature significant yet problematic in environmental contexts.

Acidic Oxides

Acidic oxides are known for their ability to react with bases to form salts and water. These oxides are generally formed from non-metal elements and can dissolve in water to form acidic solutions or react directly with bases to neutralize them.
For instance, carbon dioxide (CO₂), sulfur dioxide (SO₂), and boron trioxide (B₂O₃) are well-known acidic oxides. The exercise identifies CO₂ and B₂O₃ as acidic oxides, where CO₂ reacts with sodium hydroxide (NaOH) as shown in:

• \[ \text{CO}_2 + 2\text{NaOH} \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} \]

These reactions showcase their capacity to neutralize basic compounds.
Silicon dioxide (SiO₂) is another example, though it doesn't dissolve well in water, it reacts with molten bases like sodium hydroxide. Remembering these characteristics helps in predicting the behavior of non-metal oxides in chemical reactions.

Basic Oxides

Basic oxides are counterparts to acidic oxides and generally derive from metals. These oxides react with acids in a neutralization reaction to produce salt and water. The behavior of basic oxides is largely influenced by the electropositive nature of the metal atoms they are paired with. This makes them ready to take in protons from acids, resulting in a salt.
Common examples of basic oxides include magnesium oxide (MgO) and calcium oxide (CaO). In the exercise, thallium(III) oxide (Tl₂O₃) was classified as a basic oxide due to its reaction with hydrochloric acid (HCl):

• \[ \text{Tl}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{TlCl}_3 + 3\text{H}_2\text{O} \]

This shows that Tl₂O₃ can react with an acid to form a salt (TlCl₃) and water.
Recognizing basic oxides is key in understanding many biological processes and industrial applications, like lime in agriculture to neutralize acidic soils.

Amphoteric Oxides

Amphoteric oxides are unique as they can behave both as acidic and basic oxides. These oxides can react with both acids and bases, making them versatile in a chemical context. Examples include aluminum oxide (Al₂O₃) and zinc oxide (ZnO).
Amphoteric oxides like Al₂O₃ can react with hydrochloric acid to form aluminum chloride and water, or with sodium hydroxide to form sodium aluminate and water, as illustrated:

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

Lead(IV) oxide (PbO₂) exhibits this behavior as well, reacting with both acids and bases.
Understanding the amphoteric nature of these oxides is particularly valuable in metallurgy and chemistry as it allows for diverse reactions and applications in various processes.