Question

What is the anhydride for each of the following acids: (a) \(\mathrm{H}_{2} \mathrm{SO}_{4}\), (b) \(\mathrm{HClO}_{3}\), (c) \(\mathrm{HNO}_{2}\), (d) \(\mathrm{H}_{2} \mathrm{CO}_{3}\), (e) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) ?

Short answer

The anhydrides for the given acids are: (a) \(\mathrm{H}_{2}\mathrm{S}_{2}\mathrm{O}_{7}\), (b) \(\mathrm{Cl}_{2}\mathrm{O}_{6}\), (c) \(\mathrm{N}_{2}\mathrm{O}_{3}\), (d) \(\mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{5}\), and (e) \(\mathrm{H}_{4}\mathrm{P}_{2}\mathrm{O}_{7}\).

Step-by-step solution

(a) Find the anhydride of \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

To find the anhydride for sulfuric acid, \(\mathrm{H}_{2}\mathrm{SO}_{4}\), combine two molecules of the acid and remove one \(\mathrm{H}_{2}\mathrm{O}\) molecule: \(2 \times \mathrm{H}_{2} \mathrm{SO}_{4} - \mathrm{H}_{2}\mathrm{O} = \mathrm{H}_{2}\mathrm{S}_{2}\mathrm{O}_{7}\) The anhydride for sulfuric acid is \(\mathrm{H}_{2}\mathrm{S}_{2}\mathrm{O}_{7}\).

(b) Find the anhydride of \(\mathrm{HClO}_{3}\)

To find the anhydride for chloric acid, \(\mathrm{HClO}_{3}\), combine two molecules of the acid and remove one \(\mathrm{H}_{2}\mathrm{O}\) molecule: \(2 \times \mathrm{HClO}_{3} - \mathrm{H}_{2}\mathrm{O} = \mathrm{Cl}_{2}\mathrm{O}_{6}\) The anhydride for chloric acid is \(\mathrm{Cl}_{2}\mathrm{O}_{6}\).

(c) Find the anhydride of \(\mathrm{HNO}_{2}\)

To find the anhydride for nitrous acid, \(\mathrm{HNO}_{2}\), combine two molecules of the acid and remove one \(\mathrm{H}_{2}\mathrm{O}\) molecule: \(2 \times \mathrm{HNO}_{2} - \mathrm{H}_{2}\mathrm{O} = \mathrm{N}_{2}\mathrm{O}_{3}\) The anhydride for nitrous acid is \(\mathrm{N}_{2}\mathrm{O}_{3}\).

(d) Find the anhydride of \(\mathrm{H}_{2} \mathrm{CO}_{3}\)

To find the anhydride for carbonic acid, \(\mathrm{H}_{2}\mathrm{CO}_{3}\), combine two molecules of the acid and remove one \(\mathrm{H}_{2}\mathrm{O}\) molecule: \(2 \times \mathrm{H}_{2}\mathrm{CO}_{3} - \mathrm{H}_{2}\mathrm{O} = \mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{5}\) The anhydride for carbonic acid is \(\mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{5}\).

(e) Find the anhydride of \(\mathrm{H}_{3} \mathrm{PO}_{4}\)

To find the anhydride for phosphoric acid, \(\mathrm{H}_{3}\mathrm{PO}_{4}\), combine two molecules of the acid and remove one \(\mathrm{H}_{2}\mathrm{O}\) molecule: \(2 \times \mathrm{H}_{3}\mathrm{PO}_{4} - \mathrm{H}_{2}\mathrm{O} = \mathrm{H}_{4}\mathrm{P}_{2}\mathrm{O}_{7}\) The anhydride for phosphoric acid is \(\mathrm{H}_{4}\mathrm{P}_{2}\mathrm{O}_{7}\).

Key concepts

Sulfuric Acid and Its Anhydride

Sulfuric acid, denoted as \(\mathrm{H}_2\mathrm{SO}_4\), is a highly important industrial chemical, known for its various uses in battery acid, fertilizer, and as a dehydrating agent. When it comes to its anhydride, the process involves combining two sulfuric acid molecules and removing a water molecule \(\mathrm{H}_2\mathrm{O}\), resulting in \(\mathrm{H}_2\mathrm{S}_2\mathrm{O}_7\), also known as pyrosulfuric acid or oleum. This is a useful reaction for understanding the relationship between acids and their respective anhydrides.

Oleum is used in various industrial applications, including the production of detergents and explosives. By understanding the creation of anhydrides, students can get insights into chemical synthesis and reactivity, both key concepts in chemistry.

Chloric Acid and Its Anhydride

Chloric acid, with the formula \(\mathrm{HClO}_3\), is known for its oxidative properties and is a part of a family of oxoacids of chlorine. To form its anhydride, you will combine two molecules of chloric acid and eliminate a single water molecule. This yields \(\mathrm{Cl}_2\mathrm{O}_6\), which is a powerful oxidizing agent itself.

Although less commonly encountered outside the laboratory, understanding chloric acid and its anhydride helps students grasp the varied oxidative states chlorine can exist in, offering a peek into the versatile nature of halogens in chemistry.

Nitrous Acid and Its Anhydride

Nitrous acid, \(\mathrm{HNO}_2\), is a weaker acid often used in the preparation of diazonium salts in organic synthesis. Its anhydride is formed by combining two nitrous acid molecules and removing one molecule of water, resulting in \(\mathrm{N}_2\mathrm{O}_3\), known as dinitrogen trioxide. This compound is important as it exemplifies the behavior of nitrogen oxides, which are significant in the study of environmental chemistry and atmospheric reactions.

It's critical to understand the properties and reactions of nitrous acid and its anhydride as they play a significant role in nitrogen cycles and pollution.

Carbonic Acid and Its Anhydride

Carbonic acid \(\mathrm{H}_2\mathrm{CO}_3\) plays an essential role in biological and geological processes. Like others, its anhydride is constructed by removing a water molecule from two carbonic acid molecules, which gives \(\mathrm{H}_2\mathrm{C}_2\mathrm{O}_5\), though it's more commonly recognized in the form of its gaseous counterpart, carbon dioxide \(\mathrm{CO}_2\).

This transformation is pivotal in understanding the carbon cycle and the impact of \(\mathrm{CO}_2\) in environmental science, as well as the role of acids and anhydrides in biochemical systems.

Phosphoric Acid and Its Anhydride

Phosphoric acid \(\mathrm{H}_3\mathrm{PO}_4\) is widely used in agriculture and food industries. Its anhydride, \(\mathrm{H}_4\mathrm{P}_2\mathrm{O}_7\), or pyrophosphoric acid, results from dehydrating two phosphoric acid molecules. This occurs naturally when phosphoric acid is heated, leading to the loss of a water molecule.

The anhydride form is significant in biochemistry, especially in DNA synthesis and energy transfer through ATP. For students, understanding the process of forming pyrophosphoric acid can help illustrate the concept of condensation reactions and their importance in both industrial chemistry and life sciences.