Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

With \(\mathrm{NH}_{4} \mathrm{OH}\), the silver nitrate is decomposed to give a brown precipitate of (a) \(\mathrm{Ag}_{2} \mathrm{O}\) (b) \(\mathrm{AgO}\) (c) \(\mathrm{Ag}(\mathrm{OH})_{2}\) (d) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\)

Step-by-Step Solution

Answer

The precipitate is (a) \( \mathrm{Ag}_2\mathrm{O} \).

Step 1: Write the Reaction Formula

To understand the decomposition reaction, it's important to know the chemical formula of ammonium hydroxide, which is \( \mathrm{NH}_4\mathrm{OH} \), and silver nitrate, which is \( \mathrm{AgNO}_3 \). The reaction can be written as: \[ \mathrm{AgNO}_3 + \mathrm{NH}_4\mathrm{OH} \rightarrow ? \]

Step 2: Identify the Reaction Products

The product formed from the reaction of silver nitrate with ammonium hydroxide is known to yield a brown precipitate and other products. In organic chemistry, brown precipitate often signifies silver oxide, \( \mathrm{Ag}_2\mathrm{O} \). The other product is ammonium nitrate, \( \mathrm{NH}_4\mathrm{NO}_3 \).

Step 3: Determine the Precipitate

Using the information from step 2, the brown precipitate formed in this reaction is \( \mathrm{Ag}_2\mathrm{O} \).

Step 4: Verify Using Chemical Precipitation Rules

According to solubility rules, silver oxide \( \mathrm{Ag}_2\mathrm{O} \) is insoluble in water and would form a precipitate. The other possible compounds (such as \( \mathrm{AgO} \), \( \mathrm{Ag(OH)_2} \), and \( \mathrm{NH}_4\mathrm{NO}_3 \)) either don't form as a brown precipitate in such reactions or are soluble.

Key Concepts

Decomposition Reaction

In chemistry, a decomposition reaction occurs when a single compound breaks down into two or more simpler products. This type of reaction is fundamental for understanding many chemical processes. You can identify a decomposition reaction by observing the breakdown of the reactant into multiple parts.

• Typically, decomposition reactions require an input of energy, such as heat, light, or electricity.
• They are usually represented by the general formula: \[AB \rightarrow A + B\]This shows a compound \( AB \) decomposing into components \( A \) and \( B \).

In the reaction between silver nitrate \((\mathrm{AgNO}_3)\) and ammonium hydroxide \((\mathrm{NH}_4\mathrm{OH})\), decomposition occurs. The presence of ammonium hydroxide helps to facilitate the breakdown of silver nitrate into silver oxide \((\mathrm{Ag}_2\mathrm{O})\) and ammonium nitrate \((\mathrm{NH}_4\mathrm{NO}_3)\). The formation of insoluble silver oxide manifests as a brown precipitate, providing physical evidence for the decomposition reaction taking place.

Ammonium Hydroxide

Ammonium hydroxide is a solution of ammonia in water and has the chemical formula \( \mathrm{NH}_4\mathrm{OH} \). It is a common reagent in laboratories and industrial processes.

• In water, ammonium hydroxide exists as a mixture of ammonia \((\mathrm{NH}_3)\) and water \((\mathrm{H}_2\mathrm{O})\). Due to this mixture, it behaves like a base, releasing hydroxide ions \((\mathrm{OH}^-)\) in solutions.
• This compound is often used in chemical reactions to alter the pH, act as a weak base, or facilitate certain reactions.

In the context of reacting with silver nitrate, ammonium hydroxide plays a crucial role in driving the decomposition. When combined, it helps to form the brown precipitate of silver oxide, highlighting its ability to participate actively in chemical transformations. Students studying chemistry should understand that while \( \mathrm{NH}_4\mathrm{OH} \) itself may seem simple, its role in reactions can be significant.

Silver Nitrate

Silver nitrate, \( \mathrm{AgNO}_3 \), is a versatile chemical compound commonly used in academic and research settings due to its reactivity and ease of use.

• It is highly soluble in water, which makes it ideal for various solution-based reactions.
• Silver nitrate is a source of silver ions \((\mathrm{Ag}^+)\), which can participate in creating precipitates with other compounds.

During the reaction with ammonium hydroxide, silver nitrate decomposes to form a brown precipitate of silver oxide \((\mathrm{Ag}_2\mathrm{O})\).
This specific reaction is a classic example used to illustrate precipitation and decomposition reactions in chemistry courses.
Due to silver nitrate’s ability to engage in a wide array of reactions, it is a valuable tool for studying the properties and behaviors of silver in different chemical environments.