Problem 64 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is formed when silver nitrate is treated with caustic soda? (a) \(\mathrm{Ag}_{3} \mathrm{~N}\) (b) \(\mathrm{Ag}\) (c) \(\mathrm{AgNO}_{2}\) (d) \(\mathrm{Ag}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

Silver oxide, \( \mathrm{Ag}_{2} \mathrm{O} \), is formed.

Step 1: Identify the Reaction

We need to determine the product of the reaction between silver nitrate (AgNO₃) and caustic soda (NaOH). This is a typical double displacement reaction where the ions exchange partners.

Step 2: Write the Chemical Equation

The chemical equation for the reaction is:\[ \mathrm{AgNO}_{3 (aq)} + \mathrm{NaOH}_{(aq)} \rightarrow \mathrm{AgOH}_{(s)} + \mathrm{NaNO}_{3(aq)} \]Here, silver hydroxide (AgOH) will initially form.

Step 3: Understand the Instability of AgOH

Silver hydroxide (AgOH) is not stable. It decomposes to form silver oxide (Ag₂O) and water:\[ 2 \mathrm{AgOH} \rightarrow \mathrm{Ag}_{2} \mathrm{O} + \mathrm{H}_{2} \mathrm{O} \]

Step 4: Identify the Final Product

The final product, after the decomposition of AgOH, is silver oxide (Ag₂O). Thus, the product formed when silver nitrate is treated with caustic soda is silver oxide.

Key Concepts

Silver Nitrate

Silver nitrate, represented by the formula \( \mathrm{AgNO}_{3} \), is a versatile compound used in many chemical reactions.
It is an ionic compound composed of one silver cation \( \mathrm{Ag}^{+} \) and one nitrate anion \( \mathrm{NO}_{3}^{-} \). Silver nitrate is important in laboratories because it can be used to test for the presence of chloride ions in a solution among other applications.

• Silver nitrate is typically found as a white crystalline solid.
• It dissolves easily in water, making it an aqueous solution when mixed with a suitable solvent.
• The nitrate ion is a good leaving group, facilitating reactions such as double displacement.

In the context of the double displacement reaction, silver nitrate plays a crucial role as it reacts with caustic soda, leading to the formation of an intermediate product. It is essential to understand how silver nitrate can be manipulated in reactions to predict the products accurately.

Caustic Soda

Caustic soda is more commonly known as sodium hydroxide, and its chemical formula is \( \mathrm{NaOH} \).
It is a strong base widely employed in chemical industries and laboratories. Caustic soda is known for its ability to react with various compounds, especially those containing metals, to form precipitates.

• It appears as a white solid, which is also highly soluble in water, forming a basic solution.
• Sodium hydroxide is crucial for processes such as soap making, paper production, and in chemical reactions for neutralization.
• In the described reaction, its role is to provide hydroxide ions \( \mathrm{OH}^{-} \) necessary for forming the intermediate, silver hydroxide.

The reaction between caustic soda and silver nitrate is a classic double displacement reaction, which leads to the formation of silver hydroxide. Understanding the properties and behavior of caustic soda helps predict the subsequent steps leading to the final product formation.

Chemical Equation

A chemical equation represents the reactants and products in a chemical reaction using chemical formulas.
It shows the conversion and transformation of substances through reactant-product relationships.
In the case of silver nitrate and caustic soda reacting, the initial chemical equation is:
\[ \mathrm{AgNO}_{3(aq)} + \mathrm{NaOH}_{(aq)} \rightarrow \mathrm{AgOH}_{(s)} + \mathrm{NaNO}_{3(aq)} \]
This illustrates a double displacement reaction where an exchange of ions occurs. The silver cation \( \mathrm{Ag}^{+} \) and the hydroxide \( \mathrm{OH}^{-} \) come together to form silver hydroxide \( \mathrm{AgOH} \), and sodium nitrate \( \mathrm{NaNO}_{3} \) is left formed in the solution.
Important points to remember:

• A balanced chemical equation ensures the conservation of mass according to the law of conservation of matter.
• This reaction demonstrates ionic exchange that is crucial in understanding double displacement reactions.

Knowing how to write and interpret chemical equations is fundamental in predicting and explaining the outcomes of chemical reactions.

Silver Oxide

Silver oxide, represented by the formula \( \mathrm{Ag}_{2} \mathrm{O} \), is a result of the decomposition of silver hydroxide in this reaction.
Silver hydroxide is initially formed when silver nitrate reacts with caustic soda, but due to its instability, it breaks down.
The decomposition reaction is:
\[ 2\, \mathrm{AgOH} \rightarrow \mathrm{Ag}_{2}\, \mathrm{O} + \mathrm{H}_{2}\, \mathrm{O} \]
This means that two molecules of silver hydroxide decompose to form silver oxide and water.
Notable characteristics of silver oxide include:

• It appears as a fine black or dark brown powder.
• Silver oxide is used in some batteries and can also be a catalyst in certain reactions.
• Understanding its formation is key in reaction analysis involving silver compounds.

The transformation of silver hydroxide into silver oxide encapsulates the nature of decomposition that can occur in chemical reactions, showcasing the dynamic transformations substances can undergo.