Question

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

Short answer

Based on the periodic table and properties of elements, we can predict the nature of the given oxides as follows: (a) \(\mathrm{NO}_{2}\) is an acidic oxide (formed by a non-metal), (b) \(\mathrm{CO}_{2}\) is an acidic oxide (formed by a non-metal), (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is an amphoteric oxide (aluminum exhibits amphoteric behavior), and (d) \(\mathrm{CaO}\) is a basic oxide (formed by a metal).

Step-by-step solution

(a) Predicting the nature of NO2

Nitrogen (\(\mathrm{N}\)) is a non-metal, and when non-metals form oxides, they tend to be acidic. Thus, \(\mathrm{NO}_{2}\) should be an acidic oxide.

(b) Predicting the nature of CO2

Carbon (\(\mathrm{C}\)) is also a non-metal, and as previously mentioned, non-metal oxides tend to be acidic. Therefore, \(\mathrm{CO}_{2}\) should also be an acidic oxide.

(c) Predicting the nature of Al2O3

Aluminum (\(\mathrm{Al}\)) is a metal, and when metals form oxides, they generally are basic. However, aluminum lies in between the boundary of metals and non-metals in the periodic table, resulting in it having amphoteric behavior. Amphoteric substances can act as both acids and bases depending on the environment they are in. Consequently, \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is an amphoteric oxide.

(d) Predicting the nature of CaO

Calcium (\(\mathrm{Ca}\)) is a metal. Metals usually form basic oxides, so \(\mathrm{CaO}\) should be a basic oxide.

Key concepts

Acidic Oxides

Acidic oxides are an interesting topic as these compounds typically arise from nonmetals. For example, when we look at \(\text{NO}_2\) and \(\text{CO}_2\), these are classic examples of acidic oxides.They both contain nitrogen and carbon respectively, which are non-metals. When these non-metals form oxides, they tend to show acidic properties.
In water, acidic oxides react to form acids. Take \(\text{CO}_2\): when dissolved in water, it forms carbonic acid \(\text{H}_2\text{CO}_3\). Similarly, \(\text{NO}_2\) reacts with water to form a mixture of nitric acid (\(\text{HNO}_3\)) and nitrous acid (\(\text{HNO}_2\)).Understanding the behavior of non-metal oxides helps in predicting the nature of various compounds in chemistry.

• Non-metallic elements form acidic oxides, e.g., sulfur trioxide (\(\text{SO}_3\)) → sulfuric acid (\(\text{H}_2\text{SO}_4\)).
• These oxides are usually gaseous or volatile.

This understanding is fundament in predicting reactions they might partake in.

Basic Oxides

Basic oxides generally come from metals. A metal element bonded to oxygen usually formsthis type of oxide, as seen with calcium oxide \(\text{CaO}\). When these oxides interact with water, they tend to produce hydroxides or bases.
A simple reaction example is \(\text{CaO}\) reacting with water to form calcium hydroxide (\(\text{Ca(OH)}_2\)), a strong base.This shows how basic oxides readily react to yield basic solutions. The propensity of metal oxides to neutralize acids is another indication of theirbasic nature.

• Metal oxides can be solid at room temperature.
• Most of them dissolve in water to form alkalis, e.g., sodium oxide (\(\text{Na}_2\text{O}\)) dissolves to form sodium hydroxide (\(\text{NaOH}\)).

So when encountering metal oxides, predicting their basic reactions becomes easier, knowing they typically decrease acidity.

Amphoteric Oxides

Amphoteric oxides stand out because they can show dual characteristics.That means they can act as either acidic or basic oxides, depending on their environment.An example of an amphoteric oxide is aluminum oxide, \(\text{Al}_2\text{O}_3\).
In the presence of an acid, \(\text{Al}_2\text{O}_3\) reacts like a base and in the presence of a base, it can act like an acid. This adaptability makes amphoteric oxides quite versatile.

• These oxides often come from elements that are borderline metals, or metalloids.
• Examples include zinc oxide \(\text{ZnO}\) which also shows amphoteric behavior.

Amphoteric oxides are fascinating in chemical engineering and environmental chemistry for their unique ability to neutralize either acids or bases.

Neutral Oxides

Neutral oxides, unlike the others, don’t exhibit acidic or basic tendencies.This makes them unique among oxides.They do not react with water, acids, or bases, to cause any formation of salts or hydroxides.Typical examples are water (\(\text{H}_2\text{O}\)) and nitrous oxide (\(\text{N}_2\text{O}\)) which behave inertly.
It is their partial immutableness in acidic or basic scenarios that marks these compounds as neutral.Understanding these can help in mundane to complex scenarios for chemical stability predictions.

• Oxygen does not fully combine with non-metals in neutral oxides like carbon monoxide (\(\text{CO}\)).
• These oxides are not reactive with acids or bases.

Neutral oxides serve as great examples of stable chemical behavior, not reacting unless conditions are significantly altered.