Problem 101 - A Complete Resource Book in Chemistry for JEE Main

Question

The correct order of acidic strength is (a) \(\mathrm{Cl}_{2} \mathrm{O}_{7}>\mathrm{SO}_{2}>\mathrm{P}_{4} \mathrm{O}_{10}\) (b) \(\mathrm{CO}_{2}^{2}>\mathrm{N}_{2} \mathrm{O}_{3}^{2}>\mathrm{SO}_{3}\) (c) \(\mathrm{Na}_{2} \mathrm{O}>\mathrm{MgO}>\mathrm{Al}_{2}^{3} \mathrm{O}_{3}\) (d) \(\mathrm{K}_{2} \mathrm{O}>\mathrm{CaO}>\mathrm{MgO}\)

Step-by-Step Solution

Answer

The correct order of acidic strength is (a): \(\mathrm{Cl}_{2} \mathrm{O}_{7} > \mathrm{SO}_{2} > \mathrm{P}_{4} \mathrm{O}_{10}\).

Step 1: Identify the Compounds

First, identify the compounds involved in each option. These compounds are binary oxides of non-metals and metals.

Step 2: Understanding Acidic Nature of Oxides

Determine which of the given oxides are acidic, basic, or amphoteric. Non-metal oxides such as \(\mathrm{Cl}_{2}\mathrm{O}_{7}\), \(\mathrm{SO}_{3}\), \(\mathrm{P}_{4}\mathrm{O}_{10}\) are typically acidic. Metal oxides like \(\mathrm{Na}_{2}\mathrm{O}\), \(\mathrm{CaO}\), and \(\mathrm{K}_{2}\mathrm{O}\) are generally basic. \(\mathrm{Al}_{2}\mathrm{O}_{3}\) is amphoteric.

Step 3: Evaluate Orders in Options

For option (a), \(\mathrm{Cl}_{2}\mathrm{O}_{7}, \mathrm{SO}_{2}, \mathrm{P}_{4}\mathrm{O}_{10}\) are acidic oxides. \(\mathrm{Cl}_{2}\mathrm{O}_{7}\) is a strong acid anhydride; hence it's strongly acidic. \(\mathrm{SO}_{2}\) and \(\mathrm{P}_{4}\mathrm{O}_{10}\) follow lesser and in decreasing order. For option (b), all compounds are incorrect as \(\mathrm{CO}_{2}\) and \(\mathrm{N}_{2}\mathrm{O}_{3}\) are less acidic than \(\mathrm{SO}_{3}\). Option (c), \(\mathrm{Na}_{2}\mathrm{O}\), \(\mathrm{MgO}\), and \(\mathrm{Al}_{2}\mathrm{O}_{3}\) are basic; their order is incorrect as they are not arranged in increasing acidic strength. Option (d), the order of basicity decrements from left to right, what is intended for increasing acidity which is inaccurate.

Step 4: Conclusion Based on Evaluation

From the evaluations done in step 3, options (b), (c), and (d) do not follow the trend of increasing acidity. However, option (a) correctly follows the order of acidic strength from strongest \(\mathrm{Cl}_{2}\mathrm{O}_{7}\) to weakest \(\mathrm{P}_{4}\mathrm{O}_{10}\).

Key Concepts

Acidic Oxides

Acidic oxides are typically formed by non-metals and they react with water to produce acids. A well-known example is sulfur trioxide, which reacts with water to form sulfuric acid. Common acidic oxides include:

• Carbon dioxide (\(\mathrm{CO}_2\))
• Nitrogen dioxide (\(\mathrm{NO}_2\))
• Phosphorus pentoxide (\(\mathrm{P}_4\mathrm{O}_{10}\))
• Chlorine heptoxide (\(\mathrm{Cl}_2\mathrm{O}_7\))

These oxides tend to accept electrons and act as Lewis acids. They are generally formed with elements that have high electronegativity values. The more electronegative the central atom in the oxide, the stronger its acidity.

Basic Oxides

Basic oxides are mostly composed of metals and tend to react with water to form bases, or they react with acids in neutralization reactions. These oxides are typically found at the left side of the periodic table and include oxides such as:

• Sodium oxide (\(\mathrm{Na}_2\mathrm{O}\))
• Potassium oxide (\(\mathrm{K}_2\mathrm{O}\))
• Calcium oxide, commonly known as lime (\(\mathrm{CaO}\))

Metal oxides that are basic have ions with lower electronegativity, making them eager to donate electrons. They are often called basic anhydrides because when they dissolve in water, they form hydroxides, which are basic compounds. The strength of a basic oxide is influenced by the reactivity of the metal involved. For instance, the oxides of alkali metals like potassium form stronger bases.

Amphoteric Oxides

Amphoteric oxides are unique because they can react with both acids and bases, displaying versatile chemical behavior. The most common amphoteric oxide is aluminum oxide (\(\mathrm{Al}_2\mathrm{O}_3\)), which reacts with acids like hydrochloric acid and bases such as sodium hydroxide.Other examples include:

• Zinc oxide (\(\mathrm{ZnO}\))
• Lead(II) oxide (\(\mathrm{PbO}\))
• Tin(IV) oxide (\(\mathrm{SnO}_2\))

These oxides show their ability to act like acids or bases based on the environment they are in. This property arises from their intermediate nature where they contain both a cation and an anion that can engage in proton transfer reactions.

Periodic Trends in Oxide Acidity

From the periodic table perspective, oxide acidity increases across a period and decreases down a group. This trend reflects the changes in atomic number and size, which affect the ability of the elements to accept or donate electrons. As you move across a period from left to right:

• Metals transition into non-metals.
• The metal oxides become less basic and more acidic.
• This increase in acidity occurs because non-metals gain electron affinity.

Conversely, moving down a group decreases oxide acidity as:

• Atoms increase in size.
• Their ability to attract electrons decreases.
• Their compounds become more ionic and less covalent.

Understanding these trends helps predict the chemical behavior of an element's oxide, forming a crucial part of inorganic chemistry studies.