Problem 38 - Chemistry and Chemical Reactivity

Question

Alumina, \(\mathrm{Al}_{2} \mathrm{O}_{3},\) is amphoteric. Among examples of its amphoteric character are the reactions that occur when \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is heated strongly or "fused" with acidic oxides and basic oxides. (a) Write a balanced equation for the reaction of alumina with silica, an acidic oxide, to give aluminum metasilicate, \(\mathrm{Al}_{2}\left(\mathrm{SiO}_{3}\right)_{3}\) (b) Write a balanced equation for the reaction of alumina with the basic oxide CaO to give calcium aluminate, \(\mathbf{C a}\left(\mathrm{AlO}_{2}\right)_{2}\)

Step-by-Step Solution

Answer

(a) \(\text{Al}_2\text{O}_3 + 3\text{SiO}_2 \rightarrow \text{Al}_2(\text{SiO}_3)_3\); (b) \(\text{Al}_2\text{O}_3 + 3\text{CaO} \rightarrow 3\text{Ca}(\text{AlO}_2)_2\).

Step 1: Understanding the Problem

We need to write balanced chemical equations showing the amphoteric behavior of alumina \(\text{Al}_2\text{O}_3\) when it reacts with an acidic oxide (silica) and a basic oxide (calcium oxide).

Step 1: Balance the Reaction with Silica

To form aluminum metasilicate \(\text{Al}_2(\text{SiO}_3)_3\), alumina reacts with silica \(\text{SiO}_2\). The reaction can be represented as:\[ \text{Al}_2\text{O}_3 + 3\text{SiO}_2 \rightarrow \text{Al}_2(\text{SiO}_3)_3 \] We simply combine one mole of alumina and three moles of silica to form one mole of aluminum metasilicate, which makes the equation balanced.

Step 2: Balance the Reaction with Calcium Oxide

For the formation of calcium aluminate \(\text{Ca}(\text{AlO}_2)_2\), alumina reacts with calcium oxide \(\text{CaO}\). The balanced equation for this reaction is:\[ \text{Al}_2\text{O}_3 + 3\text{CaO} \rightarrow 3\text{Ca}(\text{AlO}_2)_2 \] Here, one mole of alumina reacts with three moles of calcium oxide to yield three moles of calcium aluminate, ensuring all elements and charges are balanced in the reaction.

Key Concepts

Balanced Chemical Equations

A balanced chemical equation is a fundamental concept in chemistry, ensuring that the number of atoms for each element is the same on both sides of the equation. This follows the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. Balancing equations is crucial because it allows us to accurately represent the quantities of reactants and products involved in a chemical process.

• To balance an equation, start by counting the number of atoms of each element in the reactants and products.
• Adjust the coefficients (the numbers in front of compounds) to balance the number of atoms for each element.
• It's important to balance one element at a time and to only change the coefficients, not the subscripts in the chemical formulas.
• For instance, in the reaction of alumina with silica, the equation becomes \( \text{Al}_2\text{O}_3 + 3\text{SiO}_2 \rightarrow \text{Al}_2(\text{SiO}_3)_3 \). This equation is balanced because the number of \( \text{Al} \), \( \text{Si} \), and \( \text{O} \) atoms are equal on both sides.

Balancing chemical equations is an essential skill in chemistry that helps us understand and predict the outcomes of reactions. It ensures that we account for all atoms involved, maintaining the integrity of both the reactants and products.

Reactions of Alumina

Alumina \( \text{Al}_2\text{O}_3 \) exhibits fascinating behavior as an amphoteric compound, meaning it can react with both acids and bases. This feature makes alumina versatile as it undergoes different types of reactions depending on the reactants it encounters.

• When alumina reacts with an acidic oxide, like silica \( \text{SiO}_2 \), it forms aluminum metasilicate. The reaction is beautifully balanced as \( \text{Al}_2\text{O}_3 + 3\text{SiO}_2 \rightarrow \text{Al}_2(\text{SiO}_3)_3 \).
• In contrast, when alumina reacts with a basic oxide, such as calcium oxide \( \text{CaO} \), it leads to the formation of calcium aluminate. This reaction is represented by the equation \( \text{Al}_2\text{O}_3 + 3\text{CaO} \rightarrow 3\text{Ca}(\text{AlO}_2)_2 \).
• The ability to interact with both acidic and basic oxides showcases alumina's dual character, making it an important component in various industrial applications.

These reactions highlight the dynamic nature of alumina, adapting to different chemical environments and forming different compounds.

Acidic and Basic Oxides

Acidic and basic oxides are two major categories of oxides that play significant roles in chemical reactions. Their interaction with amphoteric compounds like alumina demonstrates the diverse chemistry of oxides.

• Acidic oxides, generally non-metallic oxides, react with bases to form salts and water. An example is silica \( \text{SiO}_2 \), which can react with alumina to form aluminum metasilicate.
• Basic oxides, typically metallic oxides, react with acids to also produce salts and water. Calcium oxide \( \text{CaO} \), a basic oxide, reacts with alumina, showcasing its basic nature by forming calcium aluminate.
• Understanding the nature and reactions of these oxides helps in comprehending broader chemical processes, from industrial applications to natural phenomena.

Recognizing these behaviors has practical implications, such as enhancing materials in construction or controlling emissions in environmental management. The combination of acidic, basic, and amphoteric oxides allows for a wide range of chemical diversity and applications.