Question

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

Short answer

X is NaOH and Y is AgNO3, so option (b) is correct.

Step-by-step solution

Understand the properties of X

The problem describes X as a deliquescent white crystalline hydroxide and a powerful cautery that can break down proteins into a pasty mass. This points towards sodium hydroxide (NaOH), known for its strong alkaline properties and ability to corrode organic tissues.

Interpret properties and reactions of the hydroxide

The hydroxide X reacts with a nitrate Y to form another hydroxide, which further decomposes into an insoluble brown oxide. This suggests the involved hydroxide and subsequent oxide could be related to metals like silver or zinc, known for forming insoluble compounds.

Examine the given options

Option (a) suggests the compound is NaOH and Zn(NO3)2. This would not fit as Zn hydroxide does not form an insoluble brown oxide. Option (b) suggests NaOH and AgNO3. Ag(OH) decomposes to Ag2O, an insoluble brown oxide, fitting the description. Option (c) and (d) have either different reactions or do not fit the decomposition description.

Confirm the correct reaction

When NaOH reacts with AgNO3, it forms AgOH, which quickly decomposes to Ag2O, a brown insoluble oxide. This matches the conditions described in the problem, where the oxide formed is insoluble and brown.

Key concepts

Hydroxide

Understanding hydroxides is key in this exercise. Hydroxides are chemical compounds containing the hydroxide ion (OH⁻).
They often exhibit basic properties.

• Deliquescence: Some hydroxides are deliquescent, meaning they can absorb moisture from the air to become a liquid. Sodium hydroxide (NaOH), for instance, is a deliquescent white crystalline solid.
• Cauterization: NaOH is known for its ability to cut or burn tissue, performing a process called cauterization. It acts by breaking down the protein structures of tissues.

These properties make sodium hydroxide an excellent candidate for \((X\) in the problem, as it's described to not only react but also change the physical nature of skin.

Nitrate Reactions

Nitrates are key players in many chemical reactions. In this exercise, a nitrate (Y) reacts with a hydroxide. Nitrates are salts or esters of nitric acid containing the nitrate ion (NO₃⁻).

• Formation of hydroxides: When paired with hydroxides, nitrates can facilitate the formation of other hydroxides. This process is crucial for many chemical transformations.
• Decomposition process: The newly formed hydroxides may decompose into oxides upon interaction with heat or through chemical reactions.

In this problem, the reaction of a nitrate like silver nitrate (AgNO₃) with sodium hydroxide initiates the formation of silver hydroxide, which rapidly transforms into silver oxide due to its instability, leading to a brown insoluble layer.

Insoluble Compounds

Insoluble compounds, like the brown oxide mentioned in the problem, are products that do not dissolve in water.

• Oxides and their stability: When silver hydroxide forms in this reaction, it readily decomposes to silver oxide, characterized by its brown color and insolubility.
• Importance of insolubility: The insolubility of the resulting brown oxide (Ag₂O) is a significant factor. Insoluble compounds often precipitate, forming a distinct layer or residue that can be physically separated from the liquid solution.

Understanding the properties of insoluble compounds leads to a better grasp of why certain materials separate out in chemical reactions, a crucial skill for chemistry students.

Cauterization

Cauterization is a process involving the burning or removal of tissue through chemical means.

• Chemical cautery: Certain chemical agents, like sodium hydroxide, are powerful cauterants. They cause immediate damage by altering protein structures, turning them into a gel-like or pasty mass.
• Applications in medicine: Traditionally used to stop bleeding or remove unwanted tissue, chemical cautery exemplifies the real-world significance of chemical reactions.

The description of \(X\) as a powerful cautery in the exercise highlights its ability to cause chemical burns, emphasizing the transformative power of chemistry in both practical applications and textbook problems.