Problem 136 - A Complete Resource Book in Chemistry for JEE Main

Question

The total number of diprotic acids among the following is [IIT 2010] \(\mathrm{H}_{3} \mathrm{PO}_{4} \quad \mathrm{H}_{2} \mathrm{SO}_{4} \quad \mathrm{H}_{3} \mathrm{PO}_{3} \mathrm{H}_{2} \mathrm{CO}_{3} \quad \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}\) \(\begin{array}{llll}\mathrm{H}_{3} \mathrm{BO}_{3} & \mathrm{H}_{3} \mathrm{PO}_{2} & \mathrm{H}_{2} \mathrm{CrO}_{4} & \mathrm{H}_{2} \mathrm{SO}_{3}\end{array}\)

Step-by-Step Solution

Answer

There are six diprotic acids among the given substances.

Step 1: Understanding Diprotic Acids

Diprotic acids are acids that can donate two protons (hydrogen ions) per molecule when dissolved in water. We need to find out which are diprotic among the given acids.

Step 2: Analyzing Each Acid

Let's look at each acid: - \(\mathrm{H}_{3} \mathrm{PO}_{4}\): Triprotic, can donate three protons.- \(\mathrm{H}_{2} \mathrm{SO}_{4}\): Diprotic, donates two protons.- \(\mathrm{H}_{3} \mathrm{PO}_{3}\): Diprotic, despite its formula, effectively donates two protons.- \(\mathrm{H}_{2} \mathrm{CO}_{3}\): Diprotic, can give two protons.- \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}\): Sulfuric acid derivative, effectively acts as a diprotic.- \(\mathrm{H}_{3} \mathrm{BO}_{3}\): Monoprotic, donates one proton.- \(\mathrm{H}_{3} \mathrm{PO}_{2}\): Monoprotic, only one hydrogen is ionizable.- \(\mathrm{H}_{2} \mathrm{CrO}_{4}\): Diprotic, can donate two protons.- \(\mathrm{H}_{2} \mathrm{SO}_{3}\): Diprotic, can donate two protons.

Step 3: Counting the Diprotic Acids

Based on the analysis, the diprotic acids are \(\mathrm{H}_{2} \mathrm{SO}_{4}\), \(\mathrm{H}_{3} \mathrm{PO}_{3}\), \(\mathrm{H}_{2} \mathrm{CO}_{3}\), \(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{7}\), \(\mathrm{H}_{2} \mathrm{CrO}_{4}\), and \(\mathrm{H}_{2} \mathrm{SO}_{3}\). This gives us a total of six diprotic acids.

Key Concepts

Proton Donation

Proton donation refers to the ability of an acid to release hydrogen ions (H\(^+\)) into a solution. This is a fundamental idea in acid-base chemistry. When an acid dissolves in water, it ionizes to give away its hydrogen ions. The tendency and capacity to donate protons define a significant part of an acid's behavior.For example, diprotic acids are a special class that can donate two hydrogen ions per molecule. A common diprotic acid is sulfuric acid (\(\mathrm{H_2SO_4}\)). When sulfuric acid dissolves in water:

• It first loses a proton to form the hydrogen sulfate ion (\(\mathrm{HSO_4^-}\)).
• Then, it can lose a second proton to form the sulfate ion (\(\mathrm{SO_4^{2-}}\)).

The ability of diprotic acids to donate two protons means they can undergo more complex reactions and have unique roles in chemical reactions.

Acid-Base Chemistry

Acid-base chemistry delves into the interactions between acids and bases. It helps explain diverse phenomena in chemistry, including how substances mix, react, and change.An acid is a substance that can donate protons, while a base is a substance that can accept them. This interplay creates various reactions known as acid-base reactions, critical in both biological and industrial processes.There are different classes of acids:

• Monoprotic, which can release one proton, like hydrochloric acid (\(\mathrm{HCl}\)
)
• Diprotic, which can release two protons, such as carbonic acid (\(\mathrm{H_2CO_3}\)
)
• Triprotic, capable of donating three protons, such as phosphoric acid (\(\mathrm{H_3PO_4}\)
)

A deeper understanding of acid-base chemistry includes knowing how concentration and strength influence acidity. Strong acids ionize completely in solutions, while weak acids do not.This insight is essential for predicting the outcomes of reactions in solutions.

Ionic Reactions in Solutions

Ionic reactions occur when ions in solutions interact, leading to the formation of new compounds. These reactions are usually fast because ions in solution are already in a state primed for interaction. When we deal with diprotic acids in ionic reactions:

• They contribute to the solution by providing two hydrogen ions.
• The sequence and conditions under which these ions are released affect the resultant compound form and properties.

Understanding these reactions involves recognizing how hydrogen ions pair with other ions or molecules in the solution. For instance, in a solution of diprotic sulfuric acid, the interaction might result in the sequence where the acid constantly dissociates into hydrogen and sulfate ions. Ionic reactions in solutions are pivotal in fields such as analytical chemistry, where they help in determining ionic conductivity or acidity of a solution. Knowing about ionic interactions lays the foundation for more complex concepts like buffering capacity and solution chemistry dynamics.