Problem 204 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of hydrogen atom(s) attached to phosphorous atom in hypophosphorous acid is \(\quad\) [2005] (a) zero (b) two (c) one (d) three

Step-by-Step Solution

Answer

One hydrogen atom is attached to the phosphorous atom in hypophosphorous acid.

Step 1: Understanding Hypophosphorous Acid

Hypophosphorous acid is represented by the chemical formula H₃PO₂. In this compound, phosphorous (P) is the central atom, bonded to other atoms including hydrogen (H) and oxygen (O).

Step 2: Analyzing the Structure of H₃PO₂

The molecular structure of H₃PO₂ consists of a phosphorus atom bonded to one oxygen atom and two hydroxyl groups (-OH). In addition, there is one phosphorous-hydrogen (P-H) bond.

Step 3: Counting Hydrogen Atoms Attached to Phosphorus

Since the molecular structure includes one P-H bond and two -OH bonds, only one hydrogen atom is directly bonded to the phosphorous atom.

Step 4: Conclusion on the Number of Hydrogen Atoms

Based on the structure of hypophosphorous acid, the number of hydrogen atoms directly attached to the phosphorous atom is one.

Key Concepts

Chemical Structure

Hypophosphorous acid, known by its chemical formula as \( \text{H}_3\text{PO}_2 \), has a unique and interesting structure. In this compound, the central atom is phosphorus. This central position makes phosphorus crucial in determining the chemical behavior of the compound. The phosphorus atom is bonded to a total of four atoms: one oxygen and three hydrogens. However, it's important to note that only one of these hydrogen atoms is directly attached to phosphorus. The other two hydrogen atoms are part of hydroxyl groups, which are represented as \(-\text{OH}\).
- The overall molecular structure of hypophosphorous acid includes:
* One P-H bond
* One P-O bond
* Two P-(OH) bonds
These bonds are critical in defining the properties and reactivity of hypophosphorous acid.

Hydrogen Bonding

Hydrogen bonding plays a subtle but significant role in the behavior of hypophosphorous acid. Although the P-H bond itself does not participate in hydrogen bonding, the presence of hydroxyl groups influences the compound's ability to form such bonds. Hydrogen bonds usually occur when a hydrogen atom is attracted to electronegative atoms like oxygen or nitrogen in a nearby molecule or within the compound itself.
- In hypophosphorous acid:
* The two hydroxyl groups contribute to potential intermolecular hydrogen bonding.
* This interaction can affect properties such as solubility and boiling point.
While these hydrogen bonds are not as strong as covalent bonds, they are crucial in determining the physical properties of this compound.

Phosphorous Compounds

Phosphorous compounds, like hypophosphorous acid, are part of a broad category of chemicals where phosphorus is a central element. These compounds are diverse, being used in various agricultural, industrial, and laboratory applications.
- Hypophosphorous acid, in particular, is noteworthy due to:
* Its reducing properties, meaning it can help in reactions to donate electrons or hydrogen.
* Its uses in electroless nickel plating and in the synthesis of phosphine type compounds.
The characteristics of phosphorous compounds vary widely depending on the oxidation state of phosphorus and the types of bonds it forms. Understanding these compounds involves recognizing how phosphorus's ability to form bonds with different elements leads to varied chemical properties.