Problem 148 - A Complete Resource Book in Chemistry for JEE Main

Question

The oxidizing power of \(\mathrm{HXO}_{4}\) type compounds of halogens is in the order (a) \(\mathrm{HIO}_{4}>\mathrm{HBrO}_{4}>\mathrm{HClO}_{4}\) (b) \(\mathrm{HIO}_{4}>\mathrm{HClO}_{4}>\mathrm{HBrO}_{4}\) (c) \(\mathrm{HBrO}_{4}>\mathrm{HIO}_{4}^{+}>\mathrm{HClO}_{4}\) (d) \(\mathrm{HClO}_{4}>\mathrm{HBrO}_{4}>\mathrm{HIO}_{4}\)

Step-by-Step Solution

Answer

The oxidizing power order is (a) \(\mathrm{HIO}_{4} > \mathrm{HBrO}_{4} > \mathrm{HClO}_{4}\).

Step 1: Understanding Oxidation States

The compounds in question are \ \(\text{HClO}_{4}, \text{HBrO}_{4}, \text{and } \text{HIO}_{4}\). In these compounds, chlorine, bromine, and iodine are in their highest oxidation states, which is +7. The higher the oxidation state, the more oxidizing power a compound usually has, although this isn't the only factor involved.

Step 2: Considering Electronegativity

Electronegativity is a key factor. As you go up the group in the periodic table, the electronegativity of halogens increases (\(\text{Cl} > \text{Br} > \text{I}\)). A more electronegative element will attract electrons more strongly and thus often has a higher oxidizing power.

Step 3: Evaluating Atom Size and Bond Strength

The size of the central atom also matters. Larger atoms form weaker bonds with oxygen. Since iodine is larger than bromine and chlorine, its \(\mathrm{IO}_4^-\) bonds are weaker than \(\mathrm{BrO}_4^-\) and \(\mathrm{ClO}_4^-\). This makes \(\mathrm{IO}_4^-\) more likely to release oxygen, making \(\mathrm{HIO}_4\) the strongest oxidizer.

Step 4: Assembling the Oxidizing Power Order

Taking electronegativity and atom size into account, \(\mathrm{HIO}_4\) has the highest oxidizing power, followed by \(\mathrm{HBrO}_4\), then \(\mathrm{HClO}_4\). This makes the correct order for oxidizing power \((a)\): \(\mathrm{HIO}_4 > \mathrm{HBrO}_4 > \mathrm{HClO}_4\).

Key Concepts

Halogen Compounds

Halogen compounds are chemical compounds that contain halogens. Halogens are elements found in group 17 of the periodic table, specifically fluorine, chlorine, bromine, iodine, and astatine. These elements are well-known for their high reactivity, especially with the elements sodium and hydrogen. The compounds formed with hydrogen, called hydrogen halides, display varying properties based on the specific halogen involved.

Among halogen compounds, those that form with oxygen are called oxyhalides. They are known for exhibiting oxidizing behavior due to the presence of oxygen. In oxyhalogen acids like \(\text{HXO}_4\), where X represents a halogen such as chlorine, bromine, or iodine, the halogen is bonded to multiple oxygen atoms. The types and structure of these bonds play a large role in determining their chemical behavior.

• Oxyhalides can act as oxidizing agents.
• The composition notably includes a central halogen atom surrounded by four oxygen atoms.
• The nature of the central halogen atom influences the oxidizing power of these compounds.

Understanding these compounds requires a look into their electron configurations and how they influence reactions.

Electronegativity

Electronegativity is a measure of how strongly an atom can attract and hold onto electrons in a chemical bond. It is a fundamental chemical property that affects how different atoms interact with one another. In the context of halogens, electronegativity decreases as we move down the group in the periodic table, meaning:

\( ext{Cl} > ext{Br} > ext{I}\)

Chlorine is the most electronegative compared to bromine and iodine. This difference in electronegativity has a direct impact on the oxidizing power of halogen compounds:

• Higher electronegativity often leads to stronger attraction of electrons.
• In oxyhalogen acids, the more electronegative halogen will often exert more influence over shared electrons in a bond.
• Greater electronegativity tends to correlate with higher oxidizing power, but it's not the only factor.

This quality of halogens is crucial in determining both their reactivity and their role as oxidizers in chemical reactions.

Oxidation States

Oxidation state, or oxidation number, refers to the degree of oxidation of an atom within a compound. For halogen compounds like \(\text{HXO}_4\) acids, the halogens are in their highest oxidation states. This state is represented by +7 for the halogens chlorine, bromine, and iodine in these compounds. It is an essential factor in their oxidizing capabilities.

Here's why oxidation states matter:

• A higher oxidation state often means a greater ability to accept electrons during a reaction, enhancing oxidizing power.
• In \(\text{HXO}_4\) compounds, halogens donate a maximum number of electrons, meaning these atoms can still gain electrons through reduction.
• The oxidation state assists in predicting reaction pathways and chemical equilibrium.

Understanding oxidation states gives insight into how and why halogen compounds behave as strong oxidizers.

Chemical Bond Strength

Chemical bond strength refers to the energy required to break a bond between two atoms. In halogen compounds, especially those formed with oxygen, bond strength plays a critical role in their chemical behaviors and properties, including oxidizing power. As we look at halogen oxyacids, bond strength varies depending on the central halogen atom.

Considerations for bond strength include:

• Larger atoms, like iodine, form weaker bonds due to increased distance between the nucleus and the bonding electrons.
• In \(\text{HXO}_4\) compounds, weaker bonds lead to a greater tendency to release oxygen.
• This ability to release oxygen relates directly to the compound's increased oxidizing power.

In summary, bond strength is a crucial factor in understanding the properties of halogen compounds and their role as oxidizing agents. It is the weakened bond strength in \(\text{HIO}_4\) that gives it significant oxidizing power, compared to \(\text{HBrO}_4\) and \(\text{HClO}_4\).