Problem 34 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Identify the correct order of acidic strengths of \(\mathrm{CO}_{2}, \mathrm{CuO}, \mathrm{CaO}, \mathrm{H}_{2} \mathrm{O}\) (a) \(\mathrm{CaO}<\mathrm{CuO}<\mathrm{H}_{2} \mathrm{O}<\mathrm{CO}_{2}\) (b) \(\mathrm{H}_{2} \mathrm{O}<\mathrm{CuO}<\mathrm{CaO}<\mathrm{CO}_{2}\) (c) \(\mathrm{CaO}<\mathrm{H}_{2} \mathrm{O}<\mathrm{CuO}<\mathrm{CO}_{2}\) (d) \(\mathrm{H}_{2} \mathrm{O}<\mathrm{CO}_{2}<\mathrm{CaO}<\mathrm{CuO}\)

Step-by-Step Solution

Answer

Correct order is (a) \(\mathrm{CaO} < \mathrm{CuO} < \mathrm{H}_{2} \mathrm{O} < \mathrm{CO}_{2}\).

Step 1: Classify the Oxides

Acidic, basic, and amphoteric properties of oxides depend on the element's position in the periodic table. \(\mathrm{CO}_{2}\) is an acidic oxide, \(\mathrm{CuO}\) is an amphoteric oxide with weak acidic properties, \(\mathrm{CaO}\) is a basic oxide, and \(\mathrm{H}_{2}\mathrm{O}\) is neutral but slightly more acidic than metals.

Step 2: Establish Relative Acidic Strength

Acidic oxides such as \(\mathrm{CO}_{2}\) tend to release \(\mathrm{H}^{+}\) ions when reacting with water. Considering the basicity of \(\mathrm{CaO}\) and the amphoteric nature of \(\mathrm{CuO}\), the order from most acidic to least acidic is: \(\mathrm{CO}_{2} > \mathrm{H}_{2}\mathrm{O} > \mathrm{CuO} > \mathrm{CaO}\).

Step 3: Compare with Given Options

From the possible answers, compare the established order \(\mathrm{CaO} < \mathrm{CuO} < \mathrm{H}_{2} \mathrm{O} < \mathrm{CO}_{2}\) to the options. The correct order corresponding to choice (a).

Step 4: Confirm Final Order

Choice (a) reflects the correct order of acidic strength: \(\mathrm{CaO} < \mathrm{CuO} < \mathrm{H}_{2} \mathrm{O} < \mathrm{CO}_{2}\). This confirms our earlier analysis.

Key Concepts

Acidic Oxide

Acidic oxides are formed when nonmetals react with oxygen. They generally showcase acidic properties by forming acids upon reaction with water. An excellent example of an acidic oxide is carbon dioxide ( CO_2 ). When CO_2 dissolves in water, it forms carbonic acid ( H_2CO_3 ), illustrating its acidic nature. These oxides can provide important insights into the molecular behavior of nonmetals:

• They most often yield acidic solutions.
• Nonmetals like sulfur, phosphorus, and nitrogen typically form acidic oxides.
• The general trend in the periodic table is that acidic oxides are found in the upper right section.

This understanding helps in predicting the chemical behavior of oxides and their reactivity patterns with water or bases.

Basic Oxide

Basic oxides, in contrast, are generally formed by metals reacting with oxygen. They display basic characteristics, often converting to bases when interacting with water. Calcium oxide ( CaO ) serves as a classic example, often termed quicklime when it is used in its basic oxide form. Recognizing the properties of basic oxides can be beneficial:

• They typically result in alkaline solutions when dissolved in water.
• Metals in groups 1 and 2 (alkali and alkaline earth metals) usually form these oxides.
• The positions of these compounds in the periodic table are typically found in the lower left section.

This pattern of behavior stems from the metals' propensity to lose electrons, thus interacting as bases.

Amphoteric Oxide

Amphoteric oxides are unique as they exhibit both acidic and basic properties. This dual nature means they can react with both acids and bases, forming salts and water. Copper(II) oxide ( CuO ) is an example of an amphoteric oxide. Understanding amphoteric oxides can make the chemical landscape clearer:

• They can neutralize both an acid and a base.
• They are usually formed by elements located in the transition metals section of the periodic table.
• The position in the periodic table can predict if an element's oxide will be amphoteric.

By being versatile in chemical reactions, these oxides play crucial roles in various industrial applications.

Periodic Table Position

The position of elements within the periodic table greatly influences their chemical properties, including the nature of the oxides they form. Generally, the acidity, basicity, or amphoterism of an oxide can be inferred from its position in the table. For example:

• Nonmetals positioned towards the right tend to form acidic oxides.
• Metals found on the left are more inclined to form basic oxides.
• Elements located in the central part, particularly transition metals, often produce amphoteric oxides.

This predictable pattern ties into broader trends, aiding in the memorization and understanding of chemical behavior across the periodic table. It establishes a dependable foundation for predicting the chemical reactions and interactions of various elements.