Problem 6 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

In a molecule of pyrophosphoric acid, the number of \(\mathrm{P}-\mathrm{OH}, \mathrm{P}=\mathrm{O}\) and \(\mathrm{P}-\mathrm{O}-\mathrm{P}\) bonds/ moiety(ies) respectively are : [Main Sep. 03, 2020 (I)] (a) 2,4 and 1 (b) 3,3 and 3 (c) 4,2 and 0 (d) 4,2 and 1

Step-by-Step Solution

Answer

There are 4 P-OH bonds, 2 P=O bonds, and 1 P-O-P bond, so the answer is (d) 4, 2, and 1.

Step 1: Understand the Compound

Pyrophosphoric acid is H₄P₂O₇. To solve this problem, we must understand the basic structure of a pyrophosphoric acid molecule.

Step 2: Analyze the Structure for P-OH Bonds

The structure of pyrophosphoric acid consists of two phosphate ( PO₄) groups linked by a shared oxygen atom. Each phosphate group typically has one P=O double bond and three other linkages that can be P-OH or P-O-P. Since 4 OH groups are part of the whole structure, there are 4 P-OH bonds in total.

Step 3: Count the P=O Bonds in the Structure

Each phosphate group has one double bond with oxygen, resulting in a total of two P=O double bonds in the pyrophosphoric acid structure.

Step 4: Identify the P-O-P Bonds

In the pyrophosphoric acid molecule ( H₄P₂O₇), the linkage between the two phosphate groups is through a single P-O-P bond. So, there is exactly one P-O-P bond.

Key Concepts

Chemical Bonding

Chemical bonding is a fundamental concept in chemistry and refers to the forces that hold atoms together in molecules and compounds. In the context of pyrophosphoric acid, understanding chemical bonding helps to elucidate how atoms connect and the stability of the molecule.

In pyrophosphoric acid, different types of bonds exist:

• P-OH Bonds: Single bonds where a phosphorus atom (P) is connected to a hydroxyl group (OH). There are four of these in pyrophosphoric acid.
• P=O Bonds: Double bonds between phosphorus and oxygen, often contributing significantly to the molecule's stability due to the strong, covalent nature of double bonds.
• P-O-P Bonds: Found in pyrophosphoric acid, where two phosphate groups are linked by a P-O-P bridge. This is a key feature, defining the connection between the two phosphate units.

Each type of bond contributes differently to the molecular properties, affecting aspects like reactivity and solubility.

Molecular Structure

Understanding the molecular structure of pyrophosphoric acid is pivotal in determining how it functions chemically. Pyrophosphoric acid has the chemical formula \[\text{H}_4\text{P}_2\text{O}_7\].

The molecule consists of two phosphate units, \(\text{PO}_4\), that are connected by an oxygen bridge. Each phosphate unit contains:

• Four oxygen atoms bonded to a phosphorus atom.
• One of these is a double-bonded oxygen, making up the P=O bond.
• Remaining are single-bonded oxygens, either as part of hydroxyl groups (P-OH) or forming a bridge to another phosphate (P-O-P).

This arrangement endows the compound with specific properties and chemical behaviors. Its molecular structure influences its ability to participate in various chemical reactions, especially in processes involving bond formation and cleavage, which are essential in many biochemical pathways.

Phosphate Group

The phosphate group, represented as \(\text{PO}_4^{3-}\), is a versatile and essential part of pyrophosphoric acid. It plays a significant role in chemistry and biology due to its reactivity and ability to form stable compounds.

In pyrophosphoric acid, each phosphate group:

• Contains a phosphorus atom covalently bonded to four oxygen atoms.
• Can form multiple types of bonds, including P=O and P-OH bonds.
• Is involved in linking with another phosphate group through a P-O-P bond.

Phosphate groups are ubiquitous in nature, forming the backbone of DNA, making them crucial for energy transfer in biochemical processes through molecules like ATP. In the context of pyrophosphoric acid, these groups account for the molecule's functionality and reactivity, anchoring its participation in both inorganic and organic reactions.

Inorganic Chemistry

Inorganic chemistry is the study of inorganic compounds, which includes a vast array of substances such as metals, minerals, and organometallic compounds. Pyrophosphoric acid is a classic example of an inorganic compound, characterized by the presence of phosphorus and oxygen elements.

Inorganic chemistry explores properties like:

• Bonding mechanisms in non-organic molecules, such as the strong covalent bonds observed in pyrophosphoric acid.
• Structural features that impact functionality, as seen in the bridging P-O-P bond in pyrophosphoric acid.
• Reactivity with other inorganic and organic substances, emphasizing the acid's role in various industrial and biological processes.

Understanding pyrophosphoric acid through the lens of inorganic chemistry allows us to appreciate its role in both laboratory and industrial settings, for example, in the manufacturing of fertilizers and in materials chemistry.