Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{H}_{3} \mathrm{PO}_{2}\) is the molecular formula of an acid of phosphorus. Its name and basicity respectively are (a) hypophosphoric acid and two (b) hypophosphorus acid and one (c) hypophosphorus acid and two (d) phosphorus acid and two

Step-by-Step Solution

Answer

(b) hypophosphorus acid and one

Step 1: Identifying Acid Type

The molecular formula given is \( \text{H}_3\text{PO}_2 \). Analyzing the structure of the acid helps in identifying it as hypophosphorous acid, which corresponds to (b) hypophosphorus acid.

Step 2: Determine Basicity

Basicity refers to the number of ionizable hydrogens in the acid molecule. From the structure \( \text{H}_3\text{PO}_2 \), it can be determined that only one hydrogen is ionizable because the other hydrogens are bonded directly to phosphorus (not replaceable in acid-base reactions), hence the basicity is one.

Key Concepts

Hypophosphorous Acid

Hypophosphorous acid is an intriguing and lesser-known acid derived from phosphorus. Its chemical formula is \(\text{H}_3\text{PO}_2\). In this structure, there are three hydrogen atoms, one phosphorus atom, and two oxygen atoms. This acid is often used in chemistry labs due to its unique properties and serves important roles in different chemical reactions. It is known for being a good reducing agent, which means it can donate electrons during a chemical reaction, helping transform other chemicals. The presence of only one oxygen sets it apart from other phosphorus acids like phosphoric acid (\(\text{H}_3\text{PO}_4\)) and phosphorous acid (\(\text{H}_3\text{PO}_3\)). This structural difference contributes to its lesser acidity compared to others.

Basicity of Acids

The concept of basicity in chemistry is defined as the number of ionizable hydrogen atoms present in an acid. This is crucial because it determines an acid's strength and behavior in chemical reactions. Many students often confuse basicity with pH, but these are different concepts. Basicity in acids can vary, typically ranging from one to more than three.

• Monobasic acids have one ionizable hydrogen.
• Dibasic acids contain two ionizable hydrogens.
• Tribasic acids have three such hydrogens.

In the case of hypophosphorous acid (\(\text{H}_3\text{PO}_2\)), the basicity is one because there is only one hydrogen that can dissociate to form a hydrogen ion (H\(^+\)). This means that in a reaction context, it can neutralize one equivalent of a base.

Ionizable Hydrogen

An ionizable hydrogen is a hydrogen atom in an acid that can be released as an H\(^{+}\) ion during a chemical reaction. These hydrogen atoms are often bonded to more electronegative atoms like oxygen, making them replaceable in reactions. In hypophosphorous acid (\(\text{H}_3\text{PO}_2\)), although three hydrogens are present, only one is ionizable. This is because the other two hydrogens are directly attached to the phosphorus atom. They are held tightly in the molecular structure and cannot be easily released as ions. This characteristic defines the basicity of hypophosphorous acid, making it monobasic.

• Only the hydrogen bonded to oxygen is typically ionizable in phosphorus acids.
• Understanding which hydrogens are ionizable can help predict an acid's reactivity.

Molecular Formula Analysis

Molecular formula analysis helps in determining the composition and properties of chemical compounds. In the case of hypophosphorous acid, analyzing its molecular formula \(\text{H}_3\text{PO}_2\) gives important insights into its behavior and reactivity. Understanding the layout and bonding within the formula reveals which hydrogens are ionizable and which are bonded directly to other atoms such as phosphorus, offering clues as to its basicity and type.

• The number of atoms of each element in a molecule gives clues about its acidity and basicity.
• Recognizing the different types of bonds can help students understand how the molecule might interact in chemical reactions.

Appreciating the molecular formula of a chemical can build a strong foundation, enabling students to predict how the substance behaves under different conditions.