Problem 98 - A Complete Resource Book in Chemistry for JEE Main

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) \(\mathrm{NaOH}, \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)

Step-by-Step Solution

Answer

(d) \(\mathrm{NaOH}, \mathrm{Al} olimits_{(\mathrm{NO}_{3})_{3}}\).

Step 1: Identify the Compound X

The compound \(X\) is described as a deliquescent white crystalline hydroxide that is a powerful cautery and breaks down proteins. This description fits \(\mathrm{NaOH}\) (sodium hydroxide) because it is hygroscopic (absorbs moisture) and reacts with proteins.

Step 2: Identify the Reaction of X

\(\mathrm{NaOH}\) reacts with a metal nitrate \(\mathrm{Y}\) to form another hydroxide, which decomposes to form an insoluble brown oxide. This oxide formation in the presence of \(\mathrm{NaOH}\) indicates the nitrate likely contains a metal that forms such an oxide.

Step 3: Match the Metal Nitrate Y with Metal Oxide

\(\mathrm{Al(NO}_{3})_{3}\) is a nitrate that fits the description because \(\mathrm{Al(OH)}_{3}\), formed when \(\mathrm{NaOH}\) reacts with \(\mathrm{Al(NO}_{3})_{3}\), is a precipitate that eventually leads to \(\mathrm{Al}_{2}\mathrm{O}_{3}\) (alumina), a brown oxide.

Step 4: Conclusion based on process of elimination

Given the options, the pair \(\mathrm{NaOH}, \mathrm{Al(NO}_{3})_{3}\) perfectly matches all the descriptions provided in the problem.

Key Concepts

Sodium Hydroxide

Sodium Hydroxide, commonly known as lye or caustic soda, is a strong base with the formula \(\text{NaOH}\). This compound is renowned for its ability to absorb moisture from the atmosphere, which is a property termed hygroscopicity. Because of this, sodium hydroxide is often used as a powerful drying agent in laboratories.

• Aside from its hygroscopic nature, sodium hydroxide is highly reactive with organic compounds, especially proteins.
• It breaks down the structure of proteins, which is why it is used as a chemical cautery in some dermal treatments.

Within chemical reactions, NaOH often serves as a strong base that can react with various acids and metal salts. In occupational scenarios such as cleaning and manufacturing, NaOH is crucial due to its aggressive cleaning properties.

Deliquescence

Deliquescence refers to the ability of certain substances to absorb moisture from the air until they dissolve completely in the absorbed water, forming a solution. This property is particularly significant in the context of sodium hydroxide, which exhibits strong deliquescence.

• When a substance like NaOH absorbs sufficient water, it can form a liquid solution, making it crucial to store it in air-tight containers.
• Deliquescent substances are used in chemical laboratories for drying gases due to their moisture-absorbing capabilities.

Deliquescence affects how certain chemicals are stored and handled. Understanding this phenomenon helps chemists predict changes in material states and anticipate reactions.

Metal Nitrates

Metal nitrates are a class of inorganic compounds that consist of a metal cation and the nitrate anion \((\text{NO}_3^- )\). They are known for being highly soluble in water and for participating in oxidation reactions. In the context of this exercise, aluminum nitrate \(\text{Al(NO}_3)_3\) is relevant.

• When reacted with bases like NaOH, metal nitrates often form metal hydroxides.
• These hydroxides can further decompose to yield metal oxides.

Aluminum nitrate, for instance, reacts with sodium hydroxide to form aluminum hydroxide \((\text{Al(OH)}_3 )\), which precipitates out of the solution as a gelatinous substance and eventually becomes aluminum oxide \((\text{Al}_2\text{O}_3 )\). Thus, metal nitrates are pivotal in forming various metal oxides through strategic chemical reactions.

Aluminum Oxide

Aluminum oxide, \(\text{Al}_2\text{O}_3\), also known as alumina, is an insoluble white solid formed as a byproduct of various chemical reactions. It is a critical component in materials science and serves several key industrial purposes.

• This compound plays a central role in refractory materials due to its high melting point and thermal stability.
• It is also a common component in sandpapers and as a catalyst in industrial chemical processes.

In chemical synthesis, aluminum oxide acts as a precursor derived from aluminum hydroxide. For instance, when aluminum nitrate reacts with sodium hydroxide, it first forms aluminum hydroxide. This compound then dehydrates upon heating to give aluminum oxide, highlighting its significance as a stable oxide form in many reactions.

Chemical Reactions

Chemical reactions describe the process by which substances interact to form new products. These interactions involve the rearrangement of atoms and typically manifest as changes in physical and chemical properties. Among the core reactions in inorganic chemistry is the transformation of metal salts into metal hydroxides and oxides.

• In the exercise at hand, sodium hydroxide reacts with aluminum nitrate, starting a sequence of reactions that illustrate the formation of new compounds through ion exchange.
• The sodium cations and nitrate anions dissociate, allowing the hydroxide ions to react with aluminum ions to form aluminum hydroxide, which further decomposes.

Understanding these processes is crucial for predicting reaction outcomes, developing synthesis pathways, and applying inorganic chemistry principles to practical situations. They illustrate the fundamental principles of predicting and balancing chemical equations.