Question

Predict whether each of the following oxides is acidic, basic, amphoteric, or neutral: (a) \(\mathrm{NO}_{2}\), (b) \(\mathrm{CO}_{2}\), (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\), (d) \(\mathrm{CaO}\)

Short answer

(a) \(\mathrm{NO}_{2}\): acidic, (b) \(\mathrm{CO}_{2}\): acidic, (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\): amphoteric, (d) \(\mathrm{CaO}\): basic

Step-by-step solution

Analyze \(\mathrm{NO}_{2}\)

Nitrogen dioxide (\(\mathrm{NO}_{2}\)) is a covalent oxide formed by nitrogen, which is a non-metal. Generally, non-metal oxides tend to be acidic in nature. These acidic oxides react with water to form an acidic solution.

Predict the nature of \(\mathrm{NO}_{2}\)

Based on our analysis in step 1, we predict that \(\mathrm{NO}_{2}\) is an acidic oxide.

Analyze \(\mathrm{CO}_{2}\)

Carbon dioxide (\(\mathrm{CO}_{2}\)) is a covalent oxide formed by carbon, which is also a non-metal. As we mentioned before, non-metal oxides are generally acidic.

Predict the nature of \(\mathrm{CO}_{2}\)

Based on our analysis in step 3, we predict that \(\mathrm{CO}_{2}\) is an acidic oxide.

Analyze \(\mathrm{Al}_{2} \mathrm{O}_{3}\)

Aluminum oxide (\(\mathrm{Al}_{2} \mathrm{O}_{3}\)) is an ionic compound formed by aluminum, which is a metal, and oxygen, which is a non-metal. Generally, metal oxides are basic in nature, and non-metal oxides are acidic. However, some metal oxides can show both acidic and basic properties, which means they are amphoteric. Aluminum falls under this category, as it is close to the metalloid region in the periodic table.

Predict the nature of \(\mathrm{Al}_{2} \mathrm{O}_{3}\)

Based on our analysis in step 5, we predict that \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is an amphoteric oxide.

Analyze \(\mathrm{CaO}\)

Calcium oxide (\(\mathrm{CaO}\)) is an ionic compound formed by calcium, which is a metal, and oxygen, which is a non-metal. As we mentioned earlier, metal oxides tend to be basic.

Predict the nature of \(\mathrm{CaO}\)

Based on our analysis in step 7, we predict that \(\mathrm{CaO}\) is a basic oxide. In summary, the given oxides have the following properties: (a) \(\mathrm{NO}_{2}\): acidic (b) \(\mathrm{CO}_{2}\): acidic (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\): amphoteric (d) \(\mathrm{CaO}\): basic

Key concepts

Non-metal Oxides

Non-metal oxides are fascinating compounds, as they often exhibit acidic properties. This means that when they react with water, they typically form acidic solutions. Let's delve into this with practical examples:

• Take nitrogen dioxide (\(\mathrm{NO}_{2}\)) for instance. Formed from the non-metal nitrogen, it's a classic non-metal oxide.
• Another example is carbon dioxide (\(\mathrm{CO}_{2}\)), made from carbon, also a non-metal. Both of these oxides react with water, creating acidic environments.

This characteristic makes non-metal oxides distinct, as their covalent bonds tend to attract additional bonds with hydrogen, leading to the formation of acids, like nitric acid and carbonic acid. Understanding non-metal oxides and their behavior simplifies predicting their properties in chemical reactions.

Metal Oxides

Metal oxides are known for typically being basic. These are compounds formed by metals bonding with oxygen. Upon reacting with water, they often yield basic, or alkaline, solutions. For instance:

• Calcium oxide (\(\mathrm{CaO}\)) illustrates this well. Formed from the metal calcium, it produces a basic solution when in contact with water.

This is because metal oxides contain metal ions and oxide ions, the latter of which capture protons (H\(^+\)) to form water and hydroxide ions (OH). This results in basicity. A key point to remember is that most metal oxides compose what are known as ionic compounds, where ions attract oppositely charged ions, grounding their basic nature.

Amphoteric Oxides

Amphoteric oxides, such as aluminum oxide (\(\mathrm{Al}_{2}\mathrm{O}_{3}\)), display a unique versatility in chemistry, demonstrating both acidic and basic characteristics. This dual nature allows them to react with both acids and bases, which makes understanding and predicting their reactions a bit more complex.

• Aluminum oxide can react with strong acids like hydrochloric acid to form aluminum chloride and water, illustrating its basic character.
• Conversely, it can also react with strong bases like sodium hydroxide to form sodium aluminate, displaying acidic behavior.

This attribute is generally seen in elements like aluminum, which lie near the metalloid area of the periodic table. Amphoteric behavior is fascinating because it demonstrates how chemical properties are not always fixed; rather, they can adapt to the environment of the reaction.