Problem 62 - Chemistry The Central Science

Question

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

Step-by-Step Solution

Answer

The correct order of increasing acidity for the given oxides is: \(\mathrm{CaO} \rightarrow \mathrm{Al}_{2} \mathrm{O}_{3} \rightarrow \mathrm{SiO}_{2} \rightarrow \mathrm{CO}_{2} \rightarrow \mathrm{P}_{2} \mathrm{O}_{5} \rightarrow \mathrm{SO}_{3}.\)

Step 1: Identify the nature of each oxide

The given oxides are: 1. \(\mathrm{CO}_{2}\) (Carbon dioxide) - Non-metal oxide, so it is acidic in nature. 2. \(\mathrm{CaO}\) (Calcium oxide) - Metal oxide, which is basic in nature. 3. \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (Aluminum oxide) - This is a metalloid element oxide and has amphoteric nature. 4. \(\mathrm{SO}_{3}\) (Sulfur trioxide) - Non-metal oxide, so it is acidic in nature. 5. \(\mathrm{SiO}_{2}\) (Silicon dioxide) - This is a metalloid element oxide and has amphoteric nature. 6. \(\mathrm{P}_{2} \mathrm{O}_{5}\) (Phosphorus pentoxide) - Non-metal oxide, so it is acidic in nature.

Step 2: Arrange the oxides in order of acidity

Starting with the least acidic (most basic) and moving towards the most acidic, we get the following order: 1. \(\mathrm{CaO}\) (basic) 2. \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (amphoteric, leaning towards basic behavior) 3. \(\mathrm{SiO}_{2}\) (amphoteric, leaning towards acidic behavior) 4. \(\mathrm{CO}_{2}\) (acidic) 5. \(\mathrm{P}_{2} \mathrm{O}_{5}\) (strongly acidic) 6. \(\mathrm{SO}_{3}\) (strongly acidic) Therefore, the correct order of increasing acidity is: \(\mathrm{CaO} \rightarrow \mathrm{Al}_{2} \mathrm{O}_{3} \rightarrow \mathrm{SiO}_{2} \rightarrow \mathrm{CO}_{2} \rightarrow \mathrm{P}_{2} \mathrm{O}_{5} \rightarrow \mathrm{SO}_{3}.\)

Key Concepts

Chemical Properties of Oxides

Oxides are compounds that contain at least one oxygen atom and one other element. The chemical properties of oxides are largely determined by the nature of the element they're bonded to. Metals tend to form basic oxides, non-metals form acidic oxides, and metalloids can form either acidic, basic, or amphoteric oxides, which are oxides that can behave as either acids or bases.

An understanding of the periodic table is key to predicting the properties of an oxide. For instance, oxides formed with elements on the left side (e.g., calcium in \(\mathrm{CaO}\)) are typically basic, while those on the right side (such as carbon in \(\mathrm{CO}_{2}\)) are acidic. Metalloids, situated along the metal-nonmetal dividing line of the periodic table, often form amphoteric oxides (like \(\mathrm{Al}_{2} \mathrm{O}_{3}\)).

To understand reactivity, remember that acidic and basic oxides react with each other to form salts and water, which is fundamental in numerous chemical processes, including environmental reactions and industrial production.

Acidic and Basic Oxides

When exploring the nature of oxides, it's essential to differentiate between acidic and basic oxides. Acidic oxides, typically formed from non-metals, will react with bases and water to form acids. For example, \(\mathrm{CO}_{2}\) reacts with water to form carbonic acid (\(H_2CO_3\)). On the other hand, basic oxides, typically originating from metals, react with acids to create salts and water, e.g., calcium oxide (\(\mathrm{CaO}\)) reacts with hydrochloric acid (\(HCl\)) to produce calcium chloride (\(\mathrm{CaCl}_{2}\)) and water (\(H_{2}O\)).

When solving problems related to acidity and basicity, such as arranging oxides in order of acidity, it helps to consider the position of their elements in the periodic table and their resulting properties. This understanding facilitates predictions on how these oxides will interact in different chemical reactions.

Amphoteric Substances

Amphoteric substances are a unique group of compounds that can act as either an acid or a base, depending on the reacting substance. This dual nature is often found in oxides and hydroxides of metalloids and some metals, like aluminum oxide (\(\mathrm{Al}_{2} \mathrm{O}_{3}\)) and silicon dioxide (\(\mathrm{SiO}_{2}\)). Aluminum oxide, for example, can react with both acids and bases, generating salts and water in the process.

In the context of acidity, amphoteric oxides can be particularly challenging to place in a sequence, as their reaction tendencies aren't as straightforward as purely acidic or basic oxides. Understanding the amphoterism of substances is crucial, for instance, when predicting the outcome of reactions involving complex mixtures. This trait is also significant in various applications, such as metallurgy and water treatment, where control of pH is vital.