Question

Arrange the following oxides in order of increasing acidity: $$ \mathrm{CO}_{2}, \mathrm{CaO}, \mathrm{Al}_{2} \mathrm{O}_{3}, \mathrm{SO}_{3}, \mathrm{SiO}_{2}, \mathrm{P}_{2} \mathrm{O}_{5} \text {. } $$

Short answer

The oxides in order of increasing acidity are: \(\mathrm{CaO} \lt \mathrm{Al}_{2} \mathrm{O}_{3} \lt \mathrm{SiO}_{2} \lt \mathrm{P}_{2} \mathrm{O}_{5} \lt \mathrm{SO}_{3} \lt \mathrm{CO}_{2}\).

Step-by-step solution

Identify the oxides of metals and non-metals

Identify whether each oxide is a metal or non-metal oxide. Carbon dioxide (CO2) and silicon dioxide (SiO2) are both non-metal oxides. Calcium oxide (CaO) and aluminium oxide (Al2O3) are metal oxides. Sulfur trioxide (SO3) and phosphorus pentoxide (P2O5) are non-metal oxides.

List the oxides based on electronegativity

Now we will list the oxides based on the electronegativity of the elements involved: 1. Calcium Oxide (CaO) - Metal Oxide (Electronegativity of Ca = 1.00) 2. Aluminum Oxide (Al2O3) - Metal Oxide (Electronegativity of Al = 1.61) 3. Silicon Dioxide (SiO2) - Non-metal Oxide (Electronegativity of Si = 1.90) 4. Phosphorus Pentoxide (P2O5) - Non-metal Oxide (Electronegativity of P = 2.19) 5. Sulfur Trioxide (SO3) - Non-metal Oxide (Electronegativity of S = 2.58) 6. Carbon Dioxide (CO2) - Non-metal Oxide (Electronegativity of C = 2.55)

Arrange the oxides based on acidity

We will now arrange the given oxides in order of increasing acidity by considering the basic nature of metal oxides and the acidic nature of non-metal oxides along with their electronegativities: 1. Calcium Oxide (CaO) - Basic Metal Oxide 2. Aluminum Oxide (Al2O3) - Basic Metal Oxide 3. Silicon Dioxide (SiO2) - Acidic Non-metal Oxide 4. Phosphorus Pentoxide (P2O5) - Acidic Non-metal Oxide 5. Sulfur Trioxide (SO3) - Acidic Non-metal Oxide 6. Carbon Dioxide (CO2) - Acidic Non-metal Oxide The final order of the oxides based on increasing acidity is: $$\mathrm{CaO} \lt \mathrm{Al}_{2} \mathrm{O}_{3} \lt \mathrm{SiO}_{2} \lt \mathrm{P}_{2} \mathrm{O}_{5} \lt \mathrm{SO}_{3} \lt \mathrm{CO}_{2}$$

Key concepts

Metal Oxides

Metal oxides are compounds formed between metals and oxygen. These are often ionic in nature, meaning they consist of positive and negative ions. Metal oxides typically display basic characteristics. This is because, when these oxides dissolve in water, they form hydroxide ions (OH⁻). Think about calcium oxide (CaO) and aluminum oxide (Al₂O₃), for example. When added to water, calcium oxide forms calcium hydroxide, a strong base. Aluminum oxide, on the other hand, is amphoteric, which means it can react both as an acid and as a base.

• Most metal oxides are basic.
• They often contain metal cations combined with oxide anions.
• Can neutralize acids, resulting in salt and water as products.
• Some metal oxides, like aluminum oxide, can exhibit amphoteric behavior.

Understanding metal oxides' properties helps us predict how they will interact with other substances, particularly acids.

Non-metal Oxides

Non-metal oxides consist of non-metals bonded with oxygen. Unlike metal oxides, they are typically covalent compounds. This means the oxygen atoms share electrons rather than transferring them as in ionic bonds. Non-metal oxides like carbon dioxide (CO₂) and sulfur trioxide (SO₃) usually display acidic behavior.
Non-metal oxides react with water to form acids. For instance, sulfur trioxide reacts with water to produce sulfuric acid. This makes these oxides important in understanding acid rain.

• Tend to be acidic in nature.
• Often form acids when combined with water.
• Play a role in environmental processes like acid rain formation.

As we explore non-metal oxides, recognizing their inherent acidity can help us understand their impact on both industrial processes and the environment.

Electronegativity

Electronegativity is a measure of how strongly an element attracts electrons in a chemical bond. When thinking about oxides, it helps us predict their acidity or basicity. Generally, higher electronegativity corresponds to a more acidic nature, especially in non-metal oxides.
For example, sulfur in sulfur trioxide (SO₃) has a high electronegativity. This makes it strongly acidic. In contrast, calcium in calcium oxide (CaO) has low electronegativity, contributing to its basic nature. Electronegativity trends can often explain why non-metal oxides are more acidic than metal oxides.

• High electronegativity in non-metals often equals acidic oxides.
• Lower electronegativity in metals results in more basic oxides.
• Helps predict reactions and behaviors of chemical compounds.

Understanding electronegativity can simplify anticipations about chemical reactions and compound properties.

Acid-Base Character

The acid-base character of oxides determines whether a compound acts as an acid or a base. This is influenced by the element's position in the periodic table and its electronegativity.
Metal oxides, with their low electronegativity, are generally basic and can neutralize acids. Non-metal oxides, in contrast, are acidic, due to their higher electronegativity and tendency to form acidic solutions when reacting with water.
Aluminum oxide (Al₂O₃) is intriguing because it's amphoteric. This means it can act as both an acid and a base depending on the conditions, showcasing the diversity of acid-base behavior.

• Metal oxides: Typically basic, form bases with water.
• Non-metal oxides: Generally acidic, form acids with water.
• Some oxides, like aluminum oxide, are amphoteric.

Grasping the acid-base character of oxides helps in predicting their reactions and practical applications in various fields.