Problem 126 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of these is/are not true about the oxoacids of halogens? (a) All of them are good reducing agents (b) All of them are monobasic (c) They may be monobasic as well as polybasic (d) They have general formula HXOn.

Step-by-Step Solution

Answer

Statements (a) and (b) are not true.

Step 1: Understanding the Question

The oxoacids of halogens refer to acids with the general formula HXO, HXO2, HXO3, or HXO4, where X is a halogen. This question asks us to identify which statement(s) about these acids is/are incorrect.

Step 2: Evaluating Statement (a)

Statement (a) states that all oxoacids of halogens are good reducing agents. Evaluate if this is true by considering their properties. Most oxoacids of halogens act as oxidizing agents rather than reducing agents, as they typically have high electronegativity and can accept electrons. Hence, statement (a) is not true.

Step 3: Evaluating Statement (b)

Statement (b) says all oxoacids of halogens are monobasic, meaning they can donate one proton. While some are monobasic, such as hypochlorous acid (HClO), others, like perchloric acid (HClO4), are polybasic as they can donate multiple protons. Therefore, statement (b) is not true.

Step 4: Evaluating Statement (c)

Statement (c) indicates that oxoacids of halogens can be monobasic as well as polybasic. Since there are examples for both monobasic and polybasic oxoacids in halogens (e.g., HClO is monobasic and HClO4 is polybasic), this statement is true.

Step 5: Evaluating Statement (d)

Statement (d) suggests that the general formula for oxoacids of halogens is HXOn. This is true for these acids as the formula holds for hypohalous acids (HXO), halous acids (HXO2), halic acids (HXO3), and perhalic acids (HXO4). Thus, statement (d) is true.

Key Concepts

Halogen Chemistry

Halogens are a group of elements found in Group 17 of the periodic table. This group includes fluorine, chlorine, bromine, iodine, and astatine. They are known for their high reactivity, especially with metals, leading to the formation of salts. The word "halogen" itself comes from Greek roots meaning "salt-former".
Halogens are highly electronegative, with fluorine being the most electronegative element in the periodic table. This property allows them to easily attract electrons from other elements during chemical reactions. As a result, halogens often form polar covalent bonds. Another characteristic feature of halogens is their ability to exist in different oxidation states. This versatility contributes to the formation of various compounds, including a wide range of structurally diverse oxoacids.

Oxidizing Agents

In chemistry, oxidizing agents are substances that have the ability to accept electrons from other substances. They are essential in oxidation-reduction (redox) reactions, where one molecule loses electrons (is oxidized) and the other gains electrons (is reduced).
One of the notable properties of halogen oxoacids is their role as oxidizing agents. Due to the relatively high electronegativity of halogens, especially in their oxoacid forms, they tend to accept electrons easily. For example, perchloric acid (HClO₄) can act as a strong oxidizing agent in various chemical processes. Contrary to what some may assume, oxoacids of halogens are not commonly reducing agents because they are more inclined to gain rather than lose electrons.

Monobasic and Polybasic Acids

Acids are classified based on the number of hydrogen ions (protons) they can donate per molecule. Monobasic acids can donate only one hydrogen ion, whereas polybasic acids can donate more than one. Oxoacids of halogens provide examples of both monobasic and polybasic acids.
For instance:

• Monobasic acid: Hypochlorous acid (HClO) is monobasic because it can donate only one proton.
• Polybasic acid: Perchloric acid (HClO₄) is polybasic as it has the potential to release multiple hydrogen ions under specific conditions.

Recognizing the basicity of an acid is crucial in understanding its behavior in reactions and its ability to form salts. The ability to donate protons is linked to the acid's dissociation in water, influencing the pH and the nature of the acid-base equilibrium in solutions.

Halogen Oxoacid Formulas

The oxoacids of halogens have a general formula represented as HXO_n, where X is the halogen and the value of n indicates the number of oxygen atoms bonded to the halogen. This formula is fundamental in predicting the properties and reactivity of these acids.
Oxoacids include several forms based on the oxidation state of the halogen:

• Hypohalous acids (HXO): These involve the halogen in its lowest oxidation state, like hypochlorous acid (HClO).
• Halous acids (HXO₂): These have an intermediate oxidation state, such as chlorous acid (HClO₂).
• Halic acids (HXO₃): Represent halogens in a higher oxidation state, for example, chloric acid (HClO₃).
• Perhalic acids (HXO₄): These involve the halogen in its highest oxidation state, like perchloric acid (HClO₄).

This systematic naming and structural understanding can help deduce the chemical behavior and potential interactions of halogen oxoacids in various reactions.