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

The answer is (b) hypophosphorus acid and one.

Step 1: Identifying the Acid

The molecular formula provided is \( \mathrm{H}_{3} \mathrm{PO}_{2} \). By comparing this formula with known phosphorus-containing acids, it corresponds to hypophosphorous acid.

Step 2: Understanding Basicity

Basicity of an acid is determined by the number of hydrogen atoms that can be donated as protons (\(\mathrm{H}^{+} \)). In \(\mathrm{H}_{3} \mathrm{PO}_{2}\), there is only one hydrogen that is ionizable as a proton because the other two hydrogens are bound directly to phosphorus, not oxygen.

Step 3: Conclusion from the Analysis

With the understanding that \(\mathrm{H}_{3} \mathrm{PO}_{2}\) is hypophosphorous acid and has a basicity of one, the correct answer is (b) hypophosphorus acid and one.

Key Concepts

Basicity of acids

The basicity of an acid is the number of protons (also known as hydrogen ions, or \( \text{H}^+ \)) an acid can donate in a reaction. A simple way to grasp this concept is to think of it as the acid's ability to release hydrogen ions into a solution. The more ions it can release, the higher the basicity.

Basicity is a fundamental property that helps chemists understand the behavior of acids in various chemical reactions. Typically, basicity ranges from 1 and above, with 1 indicating that the acid can donate only one proton. For example, hydrochloric acid (HCl) has a basicity of one because it donates just one hydrogen ion. When an acid donates all its available protons, it contributes to the acidity of the solution.

Understanding the basicity of phosphorus-containing acids is particularly crucial because of their varied structural configurations and reactivity, which gives rise to different basicities among similar compounds. This knowledge aids in predicting reactions and designing compounds for use in chemical industries, research, and even everyday applications.

Phosphorus-containing acids

Phosphorus-containing acids are interesting and essential due to their diverse roles and applications in chemistry. They consist of phosphorus as a central atom bonded with a combination of hydrogen and oxygen atoms. Each type of phosphorus-containing acid can exhibit unique properties based on the arrangement of these atoms.

• Phosphoric Acid (H₃PO₄): This is a familiar acid used in fertilizers and food additives. It has a basicity of three, as it can donate three protons.
• Phosphorous Acid (H₃PO₃): Known for its use in synthesizing certain phosphorus compounds, it has a basicity of two.
• Hypophosphorous Acid (H₃PO₂): Less commonly encountered but significant in reducing agents and esters production, it has a basicity of one.

These acids are bound together by the strong and versatile nature of phosphorus and its ability to form multiple oxidation states. Because of this flexibility, these acids play key roles in various chemical syntheses and industrial applications. Understanding each acid’s structural makeup offers insights into its reactivity and possible uses.

Hypophosphorous acid

Hypophosphorous acid, with the chemical formula \( \text{H}_3\text{PO}_2 \), is a unique member of the phosphorus-containing acids. It is known for its singular basicity, meaning that it can donate just one hydrogen ion or proton. This limited ion donation is because two hydrogens bind directly to the phosphorus, leaving only one hydrogen ion available to participate in reactions.

This acid is typically found in the form of colorless crystals or a syrupy liquid, and it is highly soluble in water. Despite its lesser-known status compared to some phosphorus acids, hypophosphorous acid is quite important industrially. It is commonly used as a reducing agent in chemical reactions. For instance, it plays a vital role in the production of various chemicals and in facilitating reduction processes in both laboratory and industrial settings.

In summary, hypophosphorous acid stands out with its single ionizable hydrogen, offering distinct qualities and uses, particularly in the realm of reduction chemistry and the synthesis of compounds.