Problem 124 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of P-O-P and P-O-H bonds present respectively in pyrophosphoric acid molecule are (a) 2,2 (b) 1,8 (c) 1,2 (d) 1,4

Step-by-Step Solution

Answer

The correct answer is (d) 1,4. There is 1 P-O-P bond and 4 P-O-H bonds.

Step 1: Understanding Pyrophosphoric Acid's Formula

The chemical formula for pyrophosphoric acid is \( H_4P_2O_7 \). It consists of 4 hydrogen atoms, 2 phosphorus atoms, and 7 oxygen atoms.

Step 2: Recognize Structural Composition

In pyrophosphoric acid, the two phosphorus atoms are connected by an oxygen atom forming a P-O-P linkage. The remaining oxygens are linked to these phosphorus atoms.

Step 3: Counting P-O-P Bonds

Examine the structure. The P-O-P bond is formed between the two phosphorus atoms. Hence, there is exactly 1 P-O-P bond.

Step 4: Counting P-O-H Bonds

Identify the P-O-H bonds. Each of the phosphate groups in the acid ends with an -OH group, forming P-O-H bonds. There's a total of 4 P-O-H bonds in the molecule.

Key Concepts

Chemical Bonding

Understanding chemical bonding is crucial in grasping how pyrophosphoric acid is formed. Bonds are the connections between atoms that allow the formation of molecules and compounds. In pyrophosphoric acid, we primarily focus on two types of bonds: P-O-P and P-O-H. The P-O-P bond is present between phosphorus atoms, where one oxygen atom acts as a bridge. This type of bonding is a single covalent bond, sharing one pair of electrons between the atoms involved.

• Covalent Bonds: Shares electrons between atoms.
• Single Bonds: One pair of electrons shared.

On the other hand, P-O-H bonds are also present, which connect the phosphorus atoms to hydroxyl groups (-OH). This bond is similarly a covalent bond, but it involves phosphorus, oxygen, and hydrogen atoms. It is responsible for the acid’s characteristic properties.

Molecular Structure

The molecular structure of pyrophosphoric acid gives insight into its chemical properties and reactivity. Pyrophosphoric acid is composed of linked phosphate groups. It features two phosphorus atoms connected by a bridging oxygen atom, which forms a P-O-P bond. This organization is what defines its pyrophosphate nature.

• Functional Groups: Phosphate groups in acids.
• Bridging Oxygen: Links phosphorus atoms.

An important feature of its structure is that the molecule can donate hydrogen ions (protons), which is the source of its acidic nature. The P-O-H bonds at the end of the phosphate chains are part of what allows the acid to disassociate in water, releasing hydrogen ions. These structural features directly influence how the molecule interacts with other substances.

Phosphorus Compounds

Phosphorus compounds, such as pyrophosphoric acid, are essential in various chemical processes and applications. Phosphorus itself is a versatile element, capable of forming stable compounds with different elements. Its presence in pyrophosphoric acid is crucial as it defines the core of the molecule’s composition and reactivity.

• Tetraprotic Acid: Can release four protons.
• Phosphate Linkages: Key in biochemical processes.

Pyrophosphoric acid can serve as an intermediate during the formation of other phosphorus-containing compounds. In biological systems, compounds containing phosphorus are vital since they form the backbone of nucleic acids and contribute to energy transfer processes. Therefore, understanding phosphorus compounds' functionality enriches our knowledge of both chemistry and biological systems.