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), (b), and (d) are not true.

Step 1: Understand Oxoacids of Halogens

Oxoacids of halogens are acids that include oxygen, hydrogen, and at least one other element, typically one of the halogens (e.g., chlorine, bromine, iodine). Examples include hypochlorous acid (HClO), chloric acid (HClO3), etc.

Step 2: Evaluate Reducing Agent Property

Check if all oxoacids of halogens are reducing agents. Typically, higher oxidation states in oxoacids are not good reducing agents, as they tend to gain electrons instead of losing them.

Step 3: Assess Acidity Nature

Monobasic acids release one hydrogen ion (H+), while polybasic acids can release more than one. Not all oxoacids of halogens are monobasic; some can release two or more protons, making them polybasic.

Step 4: Consider the General Formula

Verify if all oxoacids fit the general formula HXOn. While this formula captures many oxoacids, it does not apply universally due to varying numbers of hydrogen and oxygen atoms.

Step 5: Evaluate Given Options

Compare each given statement against the analyzed properties: (a) All being reducing agents is incorrect, (b) being monobasic is incorrect as some are polybasic, (c) monobasic and polybasic is correct, (d) using general formula HXOn is not universally true.

Key Concepts

Reducing Agents

Reducing agents are substances that can donate electrons to another species in a chemical reaction. This process reduces the oxidation state of the element receiving the electrons. For oxoacids of halogens, the effectiveness as reducing agents mainly depends on their oxidation state.
Higher oxidation states, often found in these acids, make them poor reducing agents because these states are already oxidized. This means they lack the extra electrons needed to donate and instead are more likely to accept electrons, as they aim to reach a more stable, lower oxidation state.
This is why not all oxoacids of halogens are good reducing agents, contradicting the idea that they all possess this property.

Monobasic and Polybasic Acids

The ability of an acid to donate hydrogen ions is crucial to distinguishing between monobasic and polybasic acids. Monobasic acids can release only one hydrogen ion \(H^+\), whereas polybasic acids can release two or more such ions.
In the context of oxoacids of halogens, some acids only release one hydrogen ion per molecule, classifying them as monobasic. An example is hypochlorous acid \(HClO\).
On the other hand, acids like chloric acid \(HClO_3\) can release more than one hydrogen ion, thus being polybasic. Therefore, it is crucial to recognize that not all oxoacids are monobasic; some display polybasic behavior, which helps to explain the variability in their acidic properties.

General Formula HXOn

The general formula \(HXOn\) is an attempt to represent the composition of oxoacids of halogens. It indicates that an oxoacid consists of hydrogen \(H\), a halogen \((X)\), and oxygen \(O\), with 'n' representing the number of oxygen atoms.
However, while many oxoacids follow this formula, it's not applicable to all. The variability arises because different halogens and variations in the number of oxygens affect the formula. For instance, perchloric acid \(HClO_4\) and hypoiodous acid \(HIO\) both fit the general \text{HXO}_n\ format, yet their 'n' values differ significantly.
This variability means that the general formula is a guideline rather than a strict rule, reflecting the diversity in the structure of oxoacids of halogens.