Problem 93 - A Complete Resource Book in Chemistry for JEE Main

Question

Concentrated \(\mathrm{HNO}_{3}\) reacts with iodine to give (a) \(\mathrm{HI}\) (b) HOI (c) \(\mathrm{HOIO}_{2}\) (d) \(\mathrm{HOIO}_{3}\)

Step-by-Step Solution

Answer

Concentrated \(\mathrm{HNO}_3\) reacts with iodine to give \(\mathrm{HOIO}_3\) (option d).

Step 1: Identify the Reactants

In this reaction, we have concentrated \(\text{HNO}_3\) (Nitric acid) and iodine (\(\text{I}_2\)) as the reactants.

Step 2: Understand the Reaction Environment

Concentrated nitric acid is a strong oxidizing agent. Iodine is in its elemental form (\(\text{I}_2\)), and it is susceptible to oxidation under these conditions.

Step 3: Analyze Possible Products

In a reaction with a strong oxidizing agent like \(\text{HNO}_3\), iodine (\(\text{I}_2\)) is likely to form compounds where iodine has a higher oxidation state.

Step 4: Determine Likely Iodine Oxidation States

In the list of possible products, let's analyze the oxidation states of iodine:- In \(\text{HI}\), iodine has an oxidation state of -1.- In \(\text{HOI}\), iodine has an oxidation state of +1.- In \(\text{HOIO}_2\), iodine has an oxidation state of +5.- In \(\text{HOIO}_3\), iodine has an oxidation state of +7.

Step 5: Match Reaction Conditions to Products

Given the strong oxidizing nature of concentrated \(\text{HNO}_3\), iodine is likely to be oxidized to a higher state. Among the given options, \(\text{HOIO}_3\) is a compound where iodine is in a high oxidation state (+7), which is consistent with the action of concentrated \(\text{HNO}_3\).

Key Concepts

Iodine Oxidation States

Iodine can exhibit several oxidation states, ranging from -1 to +7, making it relatively versatile in chemical reactions. In its elemental form, iodine ( I_2 ) has an oxidation state of 0. However, when it goes through a reaction, particularly with strong oxidizing agents, its oxidation state can increase dramatically.
For instance, when iodine reacts under the conditions mentioned, it can be oxidized to states like +1, +5, or even +7, depending on the reactants and conditions. Understanding these states is key to predicting the products of iodine reactions. This adaptability in oxidation states also explains iodine's ability to form various compounds with different properties and reactivities.
In the case of reacting with concentrated nitric acid, we often expect the formation of higher oxidation state compounds due to the strong oxidizing nature of the acid.

Strong Oxidizing Agents

A strong oxidizing agent easily accepts electrons from other substances. They cause the oxidation of that substance by undergoing reduction themselves. Concentrated nitric acid ( HNO_3 ) serves as a classic example of a strong oxidizing agent.
When HNO_3 is concentrated, it aggressively oxidizes other elements, especially those with the potential to increase their oxidation states like iodine. The presence of such oxidizing agents leads iodine to form compounds with high oxidation states.
Knowing the oxidizing potential of chemicals like HNO_3 is crucial in understanding and predicting the reactions they can undergo. As they provide the necessary environment and energy to drive the oxidation process, even elements in their elemental form, like iodine, can be pushed to adopt higher oxidation states.

Redox Chemistry

Redox reactions, or oxidation-reduction reactions, are processes where the oxidation state of atoms is changed through the transfer of electrons.
In these reactions:

• Oxidation refers to the loss of electrons
• Reduction refers to the gain of electrons

In the context of iodine and nitric acid, such a reaction involves iodine atoms accepting electrons from nitric acid. This results in the transformation of iodine into compounds with higher oxidation states.
Understanding redox reactions is vital as it helps explain the interplay of electron transfer during reactions, dictating the formation of new substances. It's this electron movement and alteration of oxidation states that drive most chemical processes, making redox chemistry foundational in both industrial and natural changes.

Nitric Acid Reactions

Nitric acid ( HNO_3 ), particularly when concentrated, is known for its vigorous reactions and ability to oxidize a wide range of substances.
Being both an acid and an oxidizing agent, it can engage in a variety of unique reactions, especially when the concentration is high. In the exercise scenario, it reacts with iodine, an element that can increase its oxidation state significantly in the presence of strong oxidizers like nitric acid.
The nature of nitric acid makes it a key player in producing higher oxidation state compounds from other elements, affecting both laboratory and industrial processes. It's this dual capability of nitric acid as both an aggressive oxidizer and an acid that allows it to modify the chemical structure of elements like iodine, forming new and potentially useful compounds.