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. \(X\) 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

(b) \( \mathrm{NaOH}, \mathrm{AgNO_3} \)

Step 1: Understanding the Problem

We are given that compound \( X \) is a deliquescent white crystalline hydroxide that acts as a powerful cautery. This means it causes the break down of skin proteins into a pasty mass. Compound \( Y \) is a nitrate that reacts with \( X \) to form another hydroxide, which decomposes to yield an insoluble brown oxide.

Step 2: Identify Characteristics of Compound X

Given the properties, compound \( X \), the deliquescent white crystalline hydroxide that is a powerful cautery, is most likely \( \mathrm{NaOH} \) (sodium hydroxide). Sodium hydroxide is known for being deliquescent and having these cauterizing properties.

Step 3: Determine the Reaction Products

The reaction between \( X \) (assumed to be \( \mathrm{NaOH} \)) and \( Y \) (an unknown nitrate) forms a hydroxide that decomposes to produce an insoluble brown oxide. We need to figure out which of the nitrates in the options transforms into a compound that fits this description.

Step 4: Verify the Correct Nitrate

Among the given options, silver nitrate \( \mathrm{AgNO}_3 \) reacts with \( \mathrm{NaOH} \) to form silver oxide (\( \mathrm{Ag_2O} \)), which is a brown oxide that is insoluble in water. This aligns perfectly with the description given in the problem.

Step 5: Confirming the Answer

Sodium hydroxide (\( \mathrm{NaOH} \)) is the powerful cautery described, and it reacts with silver nitrate (\( \mathrm{AgNO}_3 \)) to form silver oxide (\( \mathrm{Ag_2O} \)), an insoluble brown layer of its oxide. Thus, \( \mathrm{X} \) and \( \mathrm{Y} \) must be the pair \( \mathrm{NaOH}, \mathrm{AgNO_3} \).

Key Concepts

Sodium Hydroxide

Sodium hydroxide, commonly known as lye or caustic soda, is a highly useful compound in various industries. It appears as a white, crystalline solid that is highly deliquescent, meaning it can absorb moisture from the environment. This property allows sodium hydroxide to dissolve readily in water, forming a strongly alkaline solution.

The alkaline nature of sodium hydroxide makes it an excellent cleaning agent. It is commonly used in household cleaners and industrial applications to remove grease, unclog drains, or as a component in soap making. Furthermore, sodium hydroxide is also known for its skill as a powerful cautery.

Cautery refers to the ability of sodium hydroxide to break down proteins in skin and flesh. This process transforms the proteins into a soft, pasty mass, which is why it must be handled with great care. With such corrosive properties, direct contact with skin should be avoided to prevent burns and damage.

Silver Nitrate

Silver nitrate is an inorganic compound with the formula \( \mathrm{AgNO}_{3} \). It is a versatile chemical that holds significance in various fields, including photography, medicine, and laboratory chemistry. Silver nitrate is a colorless, crystalline solid that is highly soluble in water.

In the context of chemical reactions, silver nitrate acts as an important reactant due to its ability to easily participate in precipitation reactions. When combined with a solution containing halides such as chloride or bromide, it forms a white precipitate of silver halides.

One interesting reaction involving silver nitrate is its interaction with sodium hydroxide, where it forms silver oxide \( \mathrm{Ag_2O} \). This leads to the formation of an insoluble brown oxide layer. This specific reaction is notably used in chemistry for educational demonstrations and to illustrate concepts like precipitation and insolubility.

Chemical Reactions

Chemical reactions are processes that involve the breaking and making of bonds to transform one or more substances into new products. These transformations are fundamental to chemistry and are classified into several types – synthesis, decomposition, single replacement, and double replacement, among others.

In the context of sodium hydroxide and silver nitrate, a double replacement reaction occurs. Here, the ions in the reactants exchange partners to form new products. The typical reaction when sodium hydroxide \( \mathrm{NaOH} \) is mixed with silver nitrate \( \mathrm{AgNO}_{3} \) results in the formation of silver oxide \( \mathrm{Ag_2O} \) and sodium nitrate \( \mathrm{NaNO}_3 \).

The process can be summarized by the equation:
\[ 2 \mathrm{NaOH} + \mathrm{AgNO}_{3} \rightarrow \mathrm{Ag_2O} + 2 \mathrm{NaNO}_3 + \mathrm{H}_2\mathrm{O} \]This reaction showcases the typical characteristics of a chemical reaction, such as the formation of a precipitate, which is an important concept in understanding reactivity and compound formation in inorganic chemistry.

Cautery Properties

In chemistry, cautery refers to the property of certain substances to cause chemical burns or transformations by breaking down tissues. Sodium hydroxide is exemplary in demonstrating such properties, which is why it is known as a powerful cautery agent.

The cautery effect of sodium hydroxide arises from its strong alkaline nature. When applied to the skin or flesh, it can denature proteins, causing them to lose their natural structure. This leads to the proteins forming a gelatinous or pasty mass that resembles a chemical burn.

Because of this ability, these properties find usage in both medical and industrial settings. In medical terms, controlled applications are sometimes used for removing warts or unwanted tissue. However, due to the associated risks, utmost care is required when handling substances with cautery properties to avoid inadvertent damage.