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) \(\mathrm{I}_{2}<\mathrm{HI}^{2}<\mathrm{ICl}<\mathrm{HIO}_{2}\) (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

The correct sequence is (d): \\(I_2 < ICl < HI < HIO_4\\).

Step 1: Determine the oxidation number of iodine in HI

In the compound HI, hydrogen has a +1 oxidation state. Since the compound is neutral, iodine must have an oxidation state of -1.

Step 2: Determine the oxidation number of iodine in I2

In the diatomic molecule I2, iodine is in its elemental form. Therefore, the oxidation number of each iodine atom in I2 is 0.

Step 3: Determine the oxidation number of iodine in ICl

In the compound ICl, chlorine is more electronegative than iodine and typically has an oxidation state of -1. Thus, iodine must have an oxidation state of +1 to balance the charge of the chlorine.

Step 4: Determine the oxidation number of iodine in HIO4

In the compound HIO4, hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2. Considering there are four oxygen atoms, the total oxidation state contribution from oxygen is -8. To neutralize this charge and considering hydrogen's +1, iodine must have an oxidation state of +7.

Step 5: Rank the oxidation numbers in increasing order

The oxidation numbers calculated were: HI: -1, I2: 0, ICl: +1, HIO4: +7. Arrange them in increasing order which results in HI < I2 < ICl < HIO4.

Key Concepts

Iodine Compounds

Iodine is a versatile element known for forming various compounds, each demonstrating unique properties and uses. Some common iodine compounds include hydrogen iodide (HI), iodine monochloride (ICl), diatomic iodine (I2), and periodic acid (HIO4). These compounds are particularly interesting because they display different oxidation states for iodine, which affects their chemical behavior and reactivity.

• Hydrogen Iodide (HI): A colorless gas prone to releasing iodide ions in a solution, making it a strong reducing agent.
• Diatomic Iodine (I2): Pure iodine exists as diatomic molecules, where shared electrons lead to an oxidation state of zero.
• Iodine Monochloride (ICl): This is an interhalogen compound used mainly for iodination in lab settings, with a distinct brown color.
• Periodic acid (HIO4): Known for its ability to oxidize, especially useful in organic chemistry for breaking carbon-carbon bonds.

Understanding these compounds and their properties is crucial for further exploration into iodine's role in chemical reactions and various industrial applications.

Chemical Reactions

Chemical reactions involving iodine compounds can showcase a variety of interesting transformations. These reactions depend heavily on the reactants available and the conditions under which they are performed. Some reactions include redox reactions, where iodine changes its oxidation state, illustrating its versatility and reactive nature. In a redox reaction, iodine compounds can either gain or lose electrons:

• Iodine in HI can be oxidized, indicating its readiness to release electrons.
• While combining I2 with other elements or compounds can lead to iodine being reduced or oxidized based on the partner compound.
• Iodine in ICl can participate in halogen exchange, displaying interhalogen reactivity.
• The oxidation of carbon by HIO4 breaks bonds selectively depending on the structure of the organic compound.

Each of these reactions highlights iodine's ability to participate in complex and varied chemical processes, making it an essential element in both organic and inorganic chemistry.

Electronegativity

Electronegativity refers to the ability of an atom to attract electrons in a bond. It plays a critical role in determining the oxidation states of elements in compounds, such as in iodine compounds. Generally, the higher the electronegativity, the stronger the atom's ability to attract electrons. In the iodine compounds discussed:

• Chlorine in ICl is more electronegative than iodine, which results in iodine having a positive oxidation state.
• In HI, hydrogen has a lower electronegativity, resulting in a negative oxidation state for iodine.
• The diatomic I2 has no electronegativity difference, contributing to an oxidation state of zero.
• In HIO4, oxygen's high electronegativity influences iodine to adopt a +7 oxidation state.

Understanding electronegativity differences helps predict how electrons are distributed in molecules, leading to a deeper comprehension of reactivity and bonding in chemical reactions.

Oxidation State

The concept of oxidation state is a fundamental principle in chemistry that reflects the charge of an atom in a compound. It is crucial in balancing chemical equations and predicting the behavior of molecules in reactions. For iodine compounds, the oxidation state indicates how many electrons iodine has gained or lost relative to its elemental form:

• In HI, iodine is at -1, reflecting its ability to gain an electron from hydrogen.
• I2's oxidation state is 0 because the two iodine atoms share electrons equally.
• In ICl, iodine shows an oxidation state of +1, since it passes some electron density to chlorine.
• HIO4 presents a +7 oxidation state for iodine, influenced by the highly electronegative oxygen pulling electrons away from iodine.

Grasping oxidation states will help you understand redox reactions and the movement of electrons in chemical processes, providing insight into reaction mechanisms and molecular interactions.