Problem 42 - A Complete Resource Book in Chemistry for JEE Main

Question

On strongly heating copper nitrate, we get (a) copper metal (b) cuprous oxide (c) cupric oxide (d) copper sulphate

Step-by-Step Solution

Answer

Cupric oxide (option c) is formed when copper nitrate is strongly heated.

Step 1: Understand Copper Nitrate Decomposition

When copper nitrate (\( \text{Cu(NO}_3\text{)}_2 \)) is heated strongly, it undergoes thermal decomposition. This process involves breaking down the compound into simpler substances.

Step 2: Identify Possible Products of Decomposition

The thermal decomposition of copper nitrate typically yields copper (II) oxide (\( \text{CuO} \)), nitrogen dioxide (\( \text{NO}_2 \)), and oxygen (\( \text{O}_2 \)). Copper (II) oxide is also known as cupric oxide.

Step 3: Write the Decomposition Reaction

The balanced chemical equation for the decomposition of copper nitrate is:\[ 2\text{Cu(NO}_3\text{)}_2 \rightarrow 2\text{CuO} + 4\text{NO}_2 + \text{O}_2 \]This equation confirms the production of cupric oxide when copper nitrate is heated.

Step 4: Match the Reaction Product with Given Options

Based on the balanced equation and the reaction products, the correct answer corresponds to option (c) cupric oxide, as this is one of the substances formed from the decomposition of copper nitrate.

Key Concepts

Thermal Decomposition

Thermal decomposition is a type of chemical reaction where a single compound breaks down into two or more simpler substances when heated. This process is driven by the input of thermal energy, which essentially "unlocks" the bonds holding the compound together. During the thermal decomposition of copper nitrate (\(\text{Cu(NO}_3\text{)}_2\)), heat causes the compound to split into copper (II) oxide (\(\text{CuO}\)), nitrogen dioxide (\(\text{NO}_2\)), and oxygen (\(\text{O}_2\)).

• A key characteristic of thermal decomposition reactions is their requirement for heat.
• The resultant substances are often simpler than the initial compound.
• The reaction often involves the release of gases. For copper nitrate, this is nitrogen dioxide and oxygen.

Understanding thermal decomposition helps connect the dots in realizing how complex substances can transform into simpler forms, particularly with the aid of heat.

Chemical Reactions

Chemical reactions represent processes where substances, known as reactants, transform into different substances, termed products. These transformations abound in everyday life and in numerous scientific contexts. In the context of copper nitrate decomposition, we explore how a specific reaction unfolds when copper nitrate is heated. Upon heating:

• Copper nitrate acts as the reactant.
• The reaction products are copper (II) oxide, nitrogen dioxide, and oxygen.
• Observable clues of this chemical reaction might include the release of reddish-brown nitrogen dioxide gas.

The essence of this reaction is the rearrangement of atoms. No atoms are lost; they simply shift from one compound to form others. Recognizing how chemical reactions function is crucial because they highlight the constant degree of change and conversion that characterizes chemical processes.

Balanced Chemical Equation

Balanced chemical equations play a vital role in understanding chemical reactions. They represent reactions in their most accurate forms, ensuring the same number of atoms for each element appear on both sides of the equation, conforming to the law of conservation of mass. For the thermal decomposition of copper nitrate, the balanced equation is written as:\[ 2\text{Cu(NO}_3\text{)}_2 \rightarrow 2\text{CuO} + 4\text{NO}_2 + \text{O}_2 \]This equation showcases:

• The use of coefficients left of compounds to indicate the number of moles involved in the reaction.
• Consistency in atom counts across reactants and products.
• The principle that mass remains constant, though substances change form.

Learning to balance chemical equations is a fundamental skill in chemistry, offering insights into not just how reactions occur but also ensuring no matter "disappears" in the process.