Problem 63 - Chemistry Central Science

Question

(a) What is meant by the terms acidic oxide and basic oxide? (b) How can we predict whether an oxide will be acidic or basic, based on its composition?

Step-by-Step Solution

Answer

(a) Acidic oxides are oxides of nonmetals that form acidic solutions when dissolved in water, such as SO2 and CO2. Basic oxides are oxides of metals that form alkaline solutions when dissolved in water, such as Na2O and MgO. (b) To predict whether an oxide is acidic or basic, identify whether the composing element is metallic (basic oxide) or non-metallic (acidic oxide) by referring to the periodic table. Exceptions like Al2O3 and ZnO, which are amphoteric, exist but are relatively rare.

Step 1: (a) Definition of Acidic Oxide and Basic Oxide

Acidic oxides are those oxides that, when dissolved in water, react with water and form an acidic solution. These are usually the oxides of nonmetals, such as sulfur, phosphorus, and carbon. Some common examples include sulfur dioxide (SO2) and carbon dioxide (CO2). Basic oxides, on the other hand, are those oxides that, when dissolved in water, react with water and produce a basic or alkaline solution. These are typically the oxides of metals, such as sodium, calcium, and magnesium. Some examples of basic oxides include sodium oxide (Na2O) and magnesium oxide (MgO).

Step 2: (b) Predicting whether an Oxide will be Acidic or Basic

To predict whether an oxide will be acidic or basic based on its composition, we can follow these general guidelines: 1. Identify the elements in the oxide and determine if they are metallic or non-metallic. You can refer to the periodic table to determine this: metals are on the left side and nonmetals are on the right side. 2. If the oxide is composed of a non-metallic element, it is likely to be an acidic oxide. If it's composed of a metallic element, it is likely to be a basic oxide. 3. There are some exceptions to this rule. Some metallic oxides, such as aluminum oxide (Al2O3) and zinc oxide (ZnO), are amphoteric, meaning they can behave as both an acid and a base depending on the chemical environment they are in. However, these exceptions are relatively rare and generally, the rule stated above holds true. By following these guidelines, you can predict the acidic or basic nature of an oxide based on its composition.

Key Concepts

Chemical Properties of Oxides

Understanding the chemical properties of oxides is crucial as it allows us to predict their behavior in different chemical reactions. Oxides, compounds consisting of oxygen and another element, display heterogeneous chemical properties depending on the nature of the element they're combined with.

Oxides are primarily classified into acidic and basic oxides based on their reactions with water. Acidic oxides, typically made up of nonmetals, react with water to form an acid. On the contrary, basic oxides combine with water to produce a base; these oxides are generally derived from metals. Oxides can exhibit other reactions as well, such as reacting with acids or bases in a neutralization reaction, or acting as catalysts in various industrial processes.

Reactions with Acids and Bases:

• Basic oxides react with acids to form salt and water, showcasing a typical acid-base neutralization reaction.
• Acidic oxides, likewise, can react with bases to also form salt and water.

Catalytic Properties:

• Some oxides, like vanadium(V) oxide, are used as catalysts in the production of sulfuric acid via the contact process.

This diverse set of reactions demonstrates the varied roles oxides play in chemistry.

Prediction of Oxide Acidity or Basicity

Predicting whether an oxide is acidic or basic can typically be achieved by examining the nature of the element bonded to oxygen. A systematic approach simplifies this prediction:

Firstly, by determining if the element is metal or nonmetal through the periodic table. Metals, found on the left side of the periodic table, usually form basic oxides. Conversely, nonmetals, situated on the right side, are prone to forming acidic oxides.

Occasionally, outermost valence electron count of an element also plays a role in predicting oxide nature. For instance, elements with few valence electrons tend to form basic oxides, whereas elements with a higher number are more likely to form acidic oxides.

Exceptions:

• Metals like aluminum and zinc form amphoteric oxides, capable of displaying both acidic and basic properties.
• Transition metals may form complex oxides that exhibit varied acid-base characteristics.

Although not without exceptions, remembering these broad classifications based on element type can substantially aid in predicting the chemical behavior of oxides.

Metallic and Nonmetallic Oxides

Distinguishing between metallic and nonmetallic oxides is another vital aspect in understanding their properties and behavior. Metallic oxides are generally basic in nature. They're often characterized by their ionic bonding, as metals tend to lose electrons and form positive ions. These oxides typically dissolve in water to produce hydroxide ions, resulting in an alkaline solution.

Nonmetallic oxides, on the other hand, tend to be acidic. Their covalent bonding is a result of nonmetals sharing electrons to attain full outer shells. When dissolved in water, these oxides commonly yield hydronium ions, creating an acidic environment.

Electrical Conductivity:

• Metallic oxides are usually better conductors of electricity compared to nonmetallic oxides, due to the movement of free electrons or ions.

Solubility:

• The solubility of oxides in water can vary: basic oxides are often soluble, forming metal hydroxides, whereas many acidic oxides are less soluble and may not readily dissolve.

Being aware of these distinctions can greatly facilitate the comprehension of chemical reactions and the properties of compounds.