Problem 45 - Chemistry: The Central Science

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) \(\mathrm{CaO}\).

Step-by-Step Solution

Answer

The chemical behavior of the given oxides are: (a) Nitrogen dioxide (NO₂) is acidic. (b) Carbon dioxide (CO₂) is acidic. (c) Aluminum oxide (Al₂O₃) is amphoteric. (d) Calcium oxide (CaO) is basic.

Step 1: Determine the Type of Elements for Each Oxide

Look at the periodic table to determine if the element in the oxide is a metal, non-metal, or one with amphoteric behavior. (a) NO₂: Nitrogen is a non-metal (b) CO₂: Carbon is a non-metal (c) Al₂O₃: Aluminum is known for having amphoteric properties (d) CaO: Calcium is a metal

Step 2: Define the Chemical Behavior of Each Oxide

Based on the types of elements found in the oxides, determine if the oxides are acidic, basic, amphoteric, or neutral. (a) NO₂: Nitrogen, being a non-metal, forms an acidic oxide. (b) CO₂: Carbon, being a non-metal, forms an acidic oxide. (c) Al₂O₃: Aluminum is known for forming amphoteric oxides. (d) CaO: Calcium, being a metal, forms a basic oxide. So, the chemical behavior of the given oxides are: (a) Nitrogen dioxide (NO₂) is acidic. (b) Carbon dioxide (CO₂) is acidic. (c) Aluminum oxide (Al₂O₃) is amphoteric. (d) Calcium oxide (CaO) is basic.

Key Concepts

Oxide Acidity

Oxide acidity plays a vital role in understanding chemical reactions and acid-base behavior. Acids are substances that can donate protons, and acidic oxides typically exhibit a readiness to accept water, forming an acid.
Non-metal oxides, like nitrogen dioxide \((NO_2)\) and carbon dioxide \((CO_2)\), often form acidic solutions when reacting with water.
For example:

• Nitrogen dioxide reacts with water to form nitrous \((HNO_2)\) and nitric acid \((HNO_3)\): \[NO_2 + H_2O \rightarrow HNO_2 + HNO_3\]
• Carbon dioxide reacts with water forming carbonic acid \((H_2CO_3)\): \[CO_2 + H_2O \rightarrow H_2CO_3\]

These types of reactions demonstrate the acidic nature of these oxides. Students should remember that oxides derived from non-metals often lead to acidity and can thus influence pH levels when dissolved in water.

Oxide Basicity

The concept of oxide basicity is fundamental in identifying basic substances. Basic oxides, typically formed by metals, can react with acids to produce salts and water. These oxides are also known to accept protons from acids.
One common example is calcium oxide \((CaO)\), a metal oxide, which reacts with water to produce calcium hydroxide \((Ca(OH)_2)\), a strong base. When calcium oxide is combined with an acidic solution, such as hydrochloric acid \(HCl\), it results in the formation of calcium chloride \((CaCl_2)\) and water. This reaction occurs as follows:

• \[CaO + H_2O \rightarrow Ca(OH)_2\]
• \[Ca(OH)_2 + 2HCl \rightarrow CaCl_2 + 2H_2O\]

Understanding basic oxides helps in predicting the outcomes of many chemical reactions and how different compounds interact with one another. It highlights the reactive properties of metallic elements forming basic oxides.

Amphoteric Oxides

Amphoteric oxides exhibit a unique behavior, as they can react both as acids and bases. This versatility makes them significant in various chemical reactions, allowing them to neutralize either acids or bases.
A popular example is aluminum oxide \(Al_2O_3\), which can behave as either an acidic or basic oxide, depending on the reacting partner. Here are some reactions to illustrate its amphoteric nature:

• As a basic oxide, reacting with hydrochloric acid: \[Al_2O_3 + 6HCl \rightarrow 2AlCl_3 + 3H_2O\]
• As an acidic oxide, reacting with sodium hydroxide: \[Al_2O_3 + 2NaOH + 3H_2O \rightarrow 2NaAl(OH)_4\]

The capability to act as either an acid or a base allows amphoteric oxides to interact flexibly with a broad range of other compounds, making them a key area of study in chemistry.

Periodic Table Analysis

Analyzing the periodic table is essential to predict the chemical behavior of oxides. Generally, elements towards the right of the periodic table form acidic oxides, while those on the left form basic oxides.
The position of an element helps in determining the type of oxide it will form:

• Non-metals, which are positioned on the right side, typically form acidic oxides, such as NO\(_2\) and CO\(_2\).
• Metals, found on the left side, tend to form basic oxides, like CaO.
• Elements located in the center, such as aluminum, are known to form amphoteric oxides.

This pattern in chemical behavior across the periodic table is a guiding principle in chemistry, helping students to predict the nature of oxides and other compounds formed by elements. Being able to effectively analyze periodic trends aids significantly in mastering oxide behavior and related chemical processes.