Problem 67 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a nitric acid anhydride? (a) \(\mathrm{N}_{2} \mathrm{O}_{5}\) (b) NO (c) \(\mathrm{NO}_{2}\) (d) \(\mathrm{N}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

The nitric acid anhydride is \( ext{N}_2 ext{O}_5\), option (a).

Step 1: Understanding Anhydrides

Anhydrides are chemical compounds that react with water to form an acid or base. In the context of acids, an anhydride is a compound formed usually by the removal of water from a more complex compound—in this case, from an acid.

Step 2: Definition of Nitric Acid Anhydride

Nitric acid (HNO3) loses water to form its anhydride. The chemical formula for nitric acid is HNO3, and losing one molecule of water (H2O) could yield the anhydride.

Step 3: Determine Formula from the Reaction

Write the chemical equation for the formation of the anhydride: \[ 2 ext{HNO}_3 ightarrow ext{N}_2 ext{O}_5 + ext{H}_2 ext{O} \]From this reaction, we see that the anhydride of nitric acid is \( ext{N}_2 ext{O}_5\).

Step 4: Check Given Options

Compare the determined formula of the anhydride, \( ext{N}_2 ext{O}_5\), with the given options:(a) \( ext{N}_2 ext{O}_5\), (b) NO, (c) \( ext{NO}_2\), and (d) \( ext{N}_2 ext{O}_3\). Option (a) \( ext{N}_2 ext{O}_5\) matches the formula of the determined nitric acid anhydride.

Key Concepts

Chemical Reactions

Chemical reactions are processes by which substances, known as reactants, are transformed into one or more different substances, called products. This transformation involves breaking old bonds and forming new ones. There are various types of chemical reactions, and understanding them is fundamental to chemistry.

Examples include:

• Combination reactions, where two or more reactants form a single product.
• Decomposition reactions, which involve a single reactant breaking down into two or more products.
• Replacement reactions, where elements in compounds are exchanged between molecules.

In the context of nitric acid anhydride, specifically, the decomposition reaction can be observed. When nitric acid ( HNO₃ ) loses water, it results in the formation of its anhydride ( N₂O₅ ). Reaction mechanisms like this showcase how reactants undergo chemical changes to yield new products through the rearrangement of atoms.

Anhydrides

Anhydrides are a specific type of chemical compound that, when combined with water, form either an acid or a base. The word 'anhydride' itself suggests the absence of water.

• In the case of acid anhydrides, they typically form by the removal of a molecule of water from acidic compounds.
• These compounds, when reacting with water, yield the parent acid. For example, acetic anhydride returns to acetic acid once it combines with water.

In the exercise, we explored the concept of nitric acid forming its anhydride, N₂O₅ , when water is removed. Anhydrides play a crucial role in various chemical processes, acting as intermediates in reactions or even catalysts in some cases. Understanding the role of water in forming and breaking these compounds is key to mastering the chemical behavior of anhydrides.

Nitric Acid Formation

Nitric acid ( HNO₃ ) is a strong acid, often used in laboratories and industries due to its highly reactive nature. Understanding its formation and decomposition is essential for grasping its behavior in chemical reactions.

The process for forming its anhydride involves removing water. This is represented by the chemical equation:\[2\text{HNO}_3 \rightarrow \text{N}_2\text{O}_5 + \text{H}_2\text{O}\]By observing this equation, it is clear that the removal of water molecules is critical in forming N₂O₅ , the anhydride of nitric acid. N₂O₅ is a significant compound in the context of nitric acid.

• It can easily revert to nitric acid when it comes into contact with water.
• This reversible reaction highlights the dynamic nature of chemical reactions and the role of anhydrides as intermediates.

Such transformations underscore the intricate interplay between water and chemical compounds in determining the properties and reactions of substances.