Problem 98 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following sequence is correct with reference to the oxidation number of iodine? (a) \(\mathrm{HI}<\mathrm{I}_{2}<\mathrm{ICl}<\mathrm{HIO}_{4}\) (b) \(\mathrm{I}_{2}<\mathrm{HI}<\mathrm{ICl}<\mathrm{HIO}_{4}^{7}\) (c) \(\mathrm{HIO}_{4}<\mathrm{ICl}<\mathrm{I}_{2}<\mathrm{HI}\) (d) \(\mathrm{I}_{2}<\mathrm{ICl}<\mathrm{HI}<\mathrm{HIO}_{4}\)

Step-by-Step Solution

Answer

Correct order is HI < I2 < ICl < HIO4 (Option a).

Step 1: Determine the Oxidation Number for HI

In hydrogen iodide (HI), the oxidation state of iodine (I) is determined by hydrogen having a +1 charge. Since the molecule is neutral, iodine must have an oxidation state of -1.

Step 2: Determine the Oxidation Number for ICl

In iodine monochloride (ICl), chlorine is typically in the -1 oxidation state. Therefore, iodine must be in the +1 oxidation state for the molecule to be neutral.

Step 3: Determine the Oxidation Number for I2

In diatomic iodine (I_2), both iodine atoms have an oxidation number of 0, as it is an elemental form with no charge.

Step 4: Determine the Oxidation Number for HIO4

In periodic acid (HIO_4), consider oxygen typically has an oxidation number of -2, and hydrogen is +1. To find iodine's oxidation number: I + 4(-2) + 1 = 0, therefore the oxidation number of iodine is +7.

Step 5: Arrange the Compounds by Iodine's Oxidation Number

Organize the compounds in order of increasing oxidation number of iodine: - HI: -1 - I2: 0 - ICl: +1 - HIO4: +7 The sequence is thus HI < I2 < ICl < HIO4.

Key Concepts

Iodine Compounds

Iodine compounds are chemical compounds where iodine is combined with other elements to form a variety of interesting and useful substances. Iodine can exist in multiple oxidation states, ranging from -1 up to +7. Each state represents a different type of compound with unique properties and chemical behaviors.

Some common iodine compounds include:

• Hydrogen iodide (HI): Iodine has an oxidation state of -1 and is a colorless gas used in organic synthesis.
• Iodine monochloride (ICl): With an oxidation state of +1, this compound is used as a reagent in the analysis of specific metals and nonmetals.
• Diatomic iodine (I₂): As the elemental form of iodine, its oxidation state is 0, and it is commonly used as a disinfectant.
• Periodic acid (HIO₄): Here, iodine is in its highest oxidation state of +7, used in organic chemistry to cleave diols.

Understanding the distinct characteristics of each compound helps chemists utilize them effectively in various chemical reactions and applications.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are chemical processes where electrons are transferred between substances, resulting in changes in their oxidation states. These reactions are fundamental in both everyday life and scientific applications.

In a redox reaction, one substance loses electrons (oxidation) while another gains electrons (reduction). For example:

• In HI, iodine undergoes reduction as it gains an electron to achieve an oxidation state of -1.
• Conversely, in ICl, iodine undergoes oxidation, losing an electron to get a +1 oxidation state.

The understanding of redox reactions is essential in analyzing the behavior of iodine compounds. By identifying the changes in oxidation states, chemists can predict the nature and outcome of chemical reactions. For example, periodic acid (HIO₄) showcases how iodine in high oxidation states can act as a strong oxidizing agent in chemical transformations.

Chemistry Education

Chemistry education introduces students to a fascinating world where matter interacts at the molecular level. Teaching concepts such as oxidation numbers and redox reactions is crucial for fostering a deep understanding of chemical principles.

These topics allow students to:

• Understand electron transfer in chemical reactions.
• Predict the behavior of chemical compounds in different environments.
• Explore the practical applications of chemistry in industries and natural processes.

Learning about iodine compounds and their oxidation numbers broadens a student's perception of chemistry beyond theoretical knowledge. Through exercises and practical examples, students engage with real-life applications and develop problem-solving skills essential for advanced scientific research and everyday life.