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) \(\mathrm{HOI}\) (c) \(\mathrm{HOIO}_{2}\) (d) \(\mathrm{HOIO}_{3}\)

Step-by-Step Solution

Answer

HOIO3

Step 1: Understanding the Reaction

We need to identify the product of the reaction between concentrated \(\mathrm{HNO}_{3}\) and iodine (I). This means determining the compound formed when these reactants interact.

Step 2: Choosing Possible Products

Consider the potential products from the reaction between \(\mathrm{HNO}_{3}\) and iodine. The given options are \(\mathrm{HI}\), \(\mathrm{HOI}\), \(\mathrm{HOIO}_{2}\), and \(\mathrm{HOIO}_{3}\).

Step 3: Analyzing Reaction With Concentrated \(\mathrm{HNO}_{3}\)

\(\mathrm{HNO}_{3}\) is a strong oxidizing agent. When it reacts with iodine, it is likely to oxidize the iodine to higher oxidation states. Therefore, hydroiodic acid (\(\mathrm{HI}\)) formation is unlikely, as this would involve reduction of iodine, not oxidation.

Step 4: Identifying Iodine Oxides

Iodine can form various oxyacids and oxides. The iodine oxidation states in \(\mathrm{HI}\), \(\mathrm{HOI}\), \(\mathrm{HOIO}_{2}\), and \(\mathrm{HOIO}_{3}\) are -1, +1, +3, and +5, respectively. \(\mathrm{HNO}_{3}\) tends to oxidize iodine to higher oxidation states.

Step 5: Identifying the Correct Product

Given the strong oxidizing nature of \(\mathrm{HNO}_{3}\), the higher oxidation state product, \(\mathrm{HOIO}_{3}\), is most consistent with the tendency of \(\mathrm{HNO}_{3}\) to produce higher oxidation state iodides. Thus, \(\mathrm{HOIO}_{3}\) is the likely product.

Key Concepts

Oxidizing Agents

In chemistry, oxidizing agents play a pivotal role in driving reactions by accepting electrons from other substances. When we talk about an oxidizing agent, we are discussing a substance that brings about oxidation by gaining electrons itself, thereby oxidizing another substance. This often results in the oxidizing agent itself being reduced; a classic tell-tale of its role in the reaction.

Concentrated nitric acid ( HNO_3 ) is a potent oxidizing agent. In this context, when HNO_3 reacts with iodine, it helps in raising the oxidation state of the iodine by making it lose electrons. This is contrary to reactions where you'd have the reducing agent cause the iodine to gain electrons instead. Because of this, substances like HNO_3 are crucial in scenarios where increasing the oxidation state of elements is necessary.

• Oxidizing agents gain electrons through reduction.
• They facilitate the oxidation of other substances.
• HNO_3 is a common and strong oxidizing agent, often used in reactions to elevate oxidation states.

Iodine Oxyacids

Iodine forms a variety of oxyacids, showcasing different oxidation states ranging from -1 to +5 and even higher under certain conditions. These oxyacids are crucial in understanding the chemistry of iodine in oxoanion forms.

The oxyacids of iodine include: HI , HOI , HOIO_2 , and HOIO_3 , where the iodine oxidation states are -1, +1, +3, and +5, respectively. As the oxidation state of iodine increases, the iodine atom forms stronger and more complex bonds with oxygen, often increasing the molecule's stability and reactivity.

In our reaction involving HNO_3 , which is focused on elevating the oxidation state, oxyacids like HOIO_3 are likely products because they represent higher oxidation states of iodine. This is key in scenarios where a strong oxidizing agent like HNO_3 is used, enhancing iodine's oxidation state and forming more oxidized products.

• Iodine can form several oxyacids with different oxidation states.
• Higher oxidation states, such as in HOIO_3 , are favored with strong oxidizing agents like HNO_3 .
• The stability and reactivity of iodine oxyacids increase as oxidation states rise.

Reaction Mechanisms

Understanding reaction mechanisms allows us to predict and rationalize the course of chemical reactions. Reaction mechanisms detail the step-by-step process through which reactants transform into products, often uncovering intermediate species and transition states in the process.

With oxidizing agents like HNO_3 , the mechanism often involves the donation of oxygen, transfer of electrons, or both. In reactions involving iodine and such a strong oxidizer, the steps might significantly vary depending on the oxidizing capability of the agent, eventually leading to different iodine oxyacids as products.

The process with HNO_3 might include initial attack on iodine, formation of intermediate iodides, and subsequent transformation into higher state oxyacids such as HOIO_3 . These mechanisms are vital to chemists who aim to understand product formation and predict reaction outcomes in various practical applications.

• Mechanisms guide understanding of how reactants turn into products.
• Strong oxidizers like HNO_3 drive complex pathways leading to elevated oxidation state products.
• Understanding mechanisms is crucial for predicting and controlling chemical reactions effectively.