Question

A deliquescent white crystalline hydroxide \(\mathrm{X} \mathrm{Tr}\) hydroxide which decomposes to give a insoluble brown layer of its oxide. \(\mathrm{X}\) is powerful cautery and breaks down the proteins of skin flesh to a pasty mass, \(\mathrm{X}\) and \(\mathrm{Y}\) are (a) \(\mathrm{NaOH}, \mathrm{AgNO}_{3}\) (b) \(\mathrm{NaOH}, \mathrm{Zn}\left(\mathrm{NO}_{2}\right)_{2}\) (c) \(\mathrm{NaOH}, \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\) (d) \(\mathrm{Ca}(\mathrm{OH})_{2} \cdot \mathrm{HgNO}_{3}\)

Short answer

(a) \(\text{NaOH}, \text{AgNO}_3\)

Step-by-step solution

Identify the Hydroxide Compound

The problem mentions a deliquescent white crystalline hydroxide \(X\) \(Tr\) that decomposes to form an insoluble brown oxide. Deliquescent compounds typically absorb moisture. \(\text{NaOH}\) is a known deliquescent substance among the options.

Analyze Decomposition Description

The question specifies that the hydroxide decomposes into an insoluble brown oxide. \(\text{NaOH}\), when exposed to air, can form \(\text{FeO(OH)}\) from iron impurities, which fits the description as \(\text{FeO(OH)}\) is an insoluble brown compound.

Consider Cauterizing Properties

It mentions that \(X\) is a powerful cautery that decomposes proteins to a pasty mass. \(\text{NaOH}\), known as lye or caustic soda, has such properties - it is corrosive and used in dissection or debridement in OTC wart removers. This further supports \(X = \text{NaOH}\).

Evaluate Possible Companion Compound \( \mathrm{Y} \)

The options list different nitrates paired with the hydroxide. Given \(X = \text{NaOH}\), we look for a compound that matches a known insoluble brown oxide. \(\text{AgNO}_3\) can form \(\text{Ag}_2\text{O}\), which is brown on decomposition. Hence, \(\text{AgNO}_3\) fits \(Y\).

Select the Correct Pair

Combining the findings, \(\text{NaOH}\) along with \(\text{AgNO}_3\) best describes the compounds \(X\) and \(Y\) given in option (a).

Key concepts

Hydroxide Decomposition

Hydroxide decomposition refers to the chemical process where a hydroxide compound breaks down into other substances. This can occur when a hydroxide absorbs water or carbon dioxide from the air. In the case of deliquescent substances like sodium hydroxide (NaOH), this process involves forming additional compounds.
Sodium hydroxide is a hygroscopic material, meaning it absorbs moisture and can deliquesce, which means to dissolve by absorbing water. Over time, or when exposed to specific environmental conditions, sodium hydroxide can decompose, particularly when air holds carbon dioxide, leading to the formation of sodium carbonate. If iron impurities were associated, it results in the brown iron oxide \( ext{FeO(OH)}\).

• Deliquescence: It absorbs water, facilitating the decomposition.
• Decomposition Products: Forms insoluble oxides that can be identified by their distinct colors, such as brown in the case of iron oxide.

Cautery Properties

QAutery properties refer to the ability of a substance to burn or destroy tissue. Sodium hydroxide, commonly known as lye or caustic soda, displays these properties. It acts as a powerful cautery because of its strong corrosive nature, capable of breaking down organic materials, including proteins in skin.
Sodium hydroxide accomplishes this by essentially denaturing the proteins in flesh, causing them to lose their structure and turn into a homogenous, softened mass. This reaction is both physical and chemical as it restructures the protein chains. It is crucial in industrial and medical applications, sometimes as a cleaning agent or in controlled medical usage for debridement.

• Causticity: Its potent reactivity makes it highly effective in breaking down organic tissues.
• Applications: Used in dissection, wart removals, and sometimes for cleaning purposes due to its protein decomposition ability.

Insoluble Oxide Formation

The formation of insoluble oxides is a significant reaction in various chemical processes. It involves the conversion of elements or compounds to oxides that do not readily dissolve in water. In our specific context, this refers to the formation of iron oxide as a result of hydroxide decomposition.
In the case given, the decomposition of sodium hydroxide in the presence of impurities can lead to the formation of iron hydroxides, which subsequently dehydrate to form iron (III) oxide-hydroxide, \( ext{FeO(OH)}\). This compound is characteristically brown and shows low solubility, explaining its description as an insoluble oxide in the original question.

• Iron Oxides: Often appear as colored compounds due to oxidation, such as the brown shade in \( ext{FeO(OH)}\).
• Environmental Formation: Typically occurs in high moisture environments that favor hydroxide breakdown.