Problem 26 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Choose the correct statement(s) among the following. (a) \(\mathrm{SnCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) is a reducing agent. (b) \(\mathrm{SnO}_{2}\) reacts with \(\mathrm{KOH}\) to form \(\mathrm{K}_{2}\left[\mathrm{Sn}(\mathrm{OH})_{6}\right]\). (c) A solution of \(\mathrm{PbCl}_{2}\) in \(\mathrm{HCl}\) contains \(\mathrm{Pb}^{2+}\) and \(\mathrm{Cl}^{-}\)ions. (d) The reaction of \(\mathrm{Pb}_{3} \mathrm{O}_{4}\) with hot dilute nitric acid to give \(\mathrm{PbO}_{2}\) is a redox reaction.

Step-by-Step Solution

Answer

Correct statements are (a), (b), and (d).

Step 1: Analyzing Statement (a)

The compound \(\mathrm{SnCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) is known to be a reducing agent. It can donate electrons to other substances, thereby reducing them, while itself getting oxidized. **Statement (a) is correct.**

Step 2: Analyzing Statement (b)

The compound \(\mathrm{SnO}_{2}\) reacts with \(\mathrm{KOH}\) to indeed form \(\mathrm{K}_{2}\left[\mathrm{Sn}(\mathrm{OH})_{6}\right]\), which is known as potassium hexahydroxostannate. **Statement (b) is correct.**

Step 3: Analyzing Statement (c)

A solution of \(\mathrm{PbCl}_{2}\) in \(\mathrm{HCl}\) would dissociate into \(\mathrm{Pb}^{2+}\) and \(\mathrm{Cl}^{-}\) ions. However, due to the presence of excess \(\mathrm{Cl}^{-}\) ions from \(\mathrm{HCl}\), a complex ion \([\mathrm{PbCl}_4]^{2-}\) may form. Thus, free \(\mathrm{Pb}^{2+}\) ions are not present. **Statement (c) is incorrect.**

Step 4: Analyzing Statement (d)

The reaction of \(\mathrm{Pb}_{3} \mathrm{O}_{4}\) with hot dilute nitric acid produces \(\mathrm{PbO}_{2}\), water, and nitrogen dioxide gas. In this process, lead is oxidized from Pb(II) to Pb(IV), and nitrogen is reduced from NO\(_3^-\) to NO\(_2\). This means both oxidation and reduction are occurring. **Statement (d) is correct.**

Key Concepts

Reducing Agents

Reducing agents play a crucial role in many chemical reactions by donating electrons to another substance. This process is known as reduction, and the reducing agent itself becomes oxidized. A common example is tin(II) chloride, \(\mathrm{SnCl_2} \cdot 2\mathrm{H_2O}\), which acts as a reducing agent.

This compound can donate electrons effectively because tin is in the +2 oxidation state, which is relatively unstable for tin. When it donates electrons, it transforms into a more stable oxidation state.

Reducing agents are vital in redox reactions where they allow other substances to gain electrons and become reduced. This concept is applied in various fields, such as industrial processes and analytical chemistry.

• Reducing agents are electron donors.
• They are oxidized themselves in the process.
• They work by transforming into a more stable oxidation state.

Redox Reactions

Redox reactions are chemical processes involving the transfer of electrons between two substances. They are characterized by two main changes: oxidation and reduction. In oxidation, a substance loses electrons, while in reduction, a substance gains electrons.

For example, when \(\mathrm{Pb_3O_4}\) reacts with dilute nitric acid, a redox reaction takes place. Here, lead moves from the +2 oxidation state in \(\mathrm{Pb_3O_4}\) to the +4 oxidation state in \(\mathrm{PbO_2}\), indicating an oxidation process.

Simultaneously, nitrogen from nitric acid reduces from NO−\(_3\) to NO\(_2\).

• Oxidation involves the loss of electrons.
• Reduction involves the gain of electrons.
• Redox reactions show the change in oxidation states.

Metal Hydroxides

Metal hydroxides are compounds consisting of metal ions and hydroxide ions. They often occur in reactions involving bases like potassium hydroxide \(\mathrm{KOH}\).
A typical reaction is the formation of \(\mathrm{K_2[Sn(OH)_6]}\) from tin(IV) oxide \(\mathrm{SnO_2}\).

In this reaction, \(\mathrm{SnO_2}\) reacts with \(\mathrm{KOH}\) forming potassium hexahydroxostannate, a metal hydroxide complex. Metal hydroxides have various applications, including use in purification processes and catalysis.

• Metal hydroxides consist of metal and hydroxide ions.
• They can form complex ions with a variety of properties.
• Metal hydroxides feature prominently in industrial applications.

Complex Ion Formation

Complex ion formation occurs when central metal ions bind with ligands to form a coordination complex. This typically involves the combination of metal cations and anions or neutral molecules that serve as ligands.

An example is the transformation of \(\mathrm{PbCl_2}\) in a chloride-rich environment, like \(\mathrm{HCl}\), forming \([\mathrm{PbCl}_4]^{2-}\). This changes the chemical properties and solubility of the ions involved.

Complex ions are significant in coordination chemistry and are useful in various applications such as catalysis, molecular recognition, and even in medical treatments.

• Complex ions involve metal ions and ligands.
• They alter the properties of the base components.
• Complex ion formation is vital in many scientific applications.