Problem 29 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The species that do not contain peroxide ions are (a) \(\mathrm{PbO}_{2}\) (b) \(\mathrm{H}_{2} \mathrm{O}_{2}\) (c) \(\mathrm{SrO}_{2}\) (d) \(\mathrm{BaO}_{2}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{PbO}_{2}\) does not contain peroxide ions.

Step 1: Identify Peroxide Definition

Begin by understanding what a peroxide is. A peroxide contains an ion with the formula \(O_2^{2-}\). This means that any compound with this ion in its structure is a peroxide compound. Chemicals that do not have this ion would not be considered peroxides.

Step 2: Analyze Each Compound

Examine each compound to see if it contains the peroxide ion \(O_2^{2-}\).- \(\mathrm{PbO}_{2}\): Lead dioxide is commonly known to contain lead in the +4 oxidation state with normal oxygens, not peroxide ions.- \(\mathrm{H}_{2} \mathrm{O}_{2}\): Hydrogen peroxide contains the \(O_2^{2-}\) ion.- \(\mathrm{SrO}_{2}\): Strontium peroxide contains the \(O_2^{2-}\) ion.- \(\mathrm{BaO}_{2}\): Barium peroxide contains the \(O_2^{2-}\) ion.

Step 3: Conclusion and Answer

Through analysis, we conclude that both \(\mathrm{H}_{2} \mathrm{O}_{2}\), \(\mathrm{SrO}_{2}\), and \(\mathrm{BaO}_{2}\) contain the \(O_2^{2-}\) ion, while \(\mathrm{PbO}_{2}\) does not contain this peroxide ion.

Key Concepts

Oxidation State

Understanding oxidation states is crucial when analyzing chemical compounds. Oxidation state refers to the charge an atom would have if all bonds it is part of were ionic. It helps in understanding the electron transfer process in compounds. This concept allows chemists to track how electrons are distributed among atoms in a substance.
For example, in the compound hydrogen peroxide \(\mathrm{H}_{2} \mathrm{O}_{2}\), oxygen is assigned an oxidation state of -1. Typically, oxygen has an oxidation state of -2 in other compounds. This difference is what signifies the presence of a peroxide ion \(O_2^{2-}\). In contrast, in lead dioxide \(\mathrm{PbO}_{2}\), the oxidation state of lead is +4, indicating normal oxide ions rather than peroxide ions.
A clear understanding of oxidation states aids significantly in identifying compound types, such as distinguishing peroxides from other oxides.

Peroxide Ion

The peroxide ion \(O_2^{2-}\) is fundamentally important in chemistry, marking the distinction between simple oxides and peroxides. This ion consists of two oxygen atoms bonded together, each sharing one extra electron, which gives the ion a -2 charge.
What sets peroxides apart is their unique oxygen-oxygen bond, which is a weak single bond. This results in peroxide compounds being more reactive than typical oxides, primarily due to this unstable bond that is easily broken to release oxygen.

• Common examples include hydrogen peroxide \(\mathrm{H}_{2} \mathrm{O}_{2}\), used as a bleaching agent and disinfectant.
• Metals like strontium and barium also form peroxides (\(\mathrm{SrO}_{2}\) and \(\mathrm{BaO}_{2}\)), characterized by the peroxide ion.

When identifying peroxides, look for this distinct \(O_2^{2-}\) ion in the chemical structure.

Chemical Compounds Analysis

Analyzing chemical compounds involves identifying key ions and functional groups within their structures. This analysis is fundamental to understanding the properties and behavior of the compounds.
To determine whether a compound is a peroxide, one must spot the \(O_2^{2-}\) ion. This can be done by closely examining the compound's formula and determining the oxidation states of its components. A compound containing this ion is a peroxide, which is crucial for categorizing chemical substances correctly.

• Lead dioxide \(\mathrm{PbO}_{2}\) lacks the \(O_2^{2-}\) ion, thus it doesn't qualify as a peroxide.
• Conversely, compounds such as hydrogen peroxide, strontium peroxide, and barium peroxide do contain the ion, manifesting their classification as peroxides.

This systematic approach ensures that students can apply these principles effectively in chemical compound analysis.