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

The correct answer is (c) cupric oxide.

Step 1: Identify the compound

We start with the compound copper nitrate, which has the chemical formula \(Cu(NO_3)_2\). This compound will decompose upon strong heating.

Step 2: Understand the decomposition reaction

On strong heating, copper nitrate \(Cu(NO_3)_2\) decomposes to form copper oxide, nitrogen dioxide, and oxygen. This is a common thermal decomposition reaction for metal nitrates.

Step 3: Write the balanced chemical equation

The chemical reaction involved is: \[ 2Cu(NO_3)_2(s) ightarrow 2CuO(s) + 4NO_2(g) + O_2(g) \] This equation indicates that copper nitrate decomposes to form copper(II) oxide, nitrogen dioxide, and oxygen.

Step 4: Determine the product of interest

From the chemical reaction, the solid product formed is copper(II) oxide, which is also known as cupric oxide. This is the main solid residue left after heating copper nitrate.

Step 5: Choose the correct option

Based on the decomposition reaction and the identification of products, option (c) cupric oxide is the product formed when copper nitrate is strongly heated.

Key Concepts

Thermal decomposition

Thermal decomposition is a fascinating chemical reaction where a single compound breaks down into two or more products when exposed to heat. This process is vital in understanding how compounds react when subjected to high temperatures. When heat is applied, energy is absorbed by the compound, which causes its chemical bonds to break. This bond-breaking leads to the formation of new compounds in simplified forms.

Thermal decomposition is not universal; it occurs only in certain types of chemical compounds, such as nitrates, carbonates, and chlorides. The temperature at which these reactions occur varies depending on the compound.

• Often requires a continuous application of heat
• Results in simpler structural products
• Metals such as copper are common in these reactions

Understanding thermal decomposition helps us predict how substances change under heat and plays a critical role in industrial processes like metal extraction.

Copper nitrate decomposition

Copper nitrate decomposition is a specific type of thermal decomposition involving copper nitrate. The chemical formula for copper nitrate is \(Cu(NO_3)_2\). When exposed to high temperatures, copper nitrate undergoes a fascinating transformation that produces several different substances.

When strongly heated, copper nitrate first breaks down to form copper(II) oxide, nitrogen dioxide, and oxygen:

• Copper(II) oxide \((CuO)\)
• Nitrogen dioxide \((NO_2)\)
• Oxygen gas \((O_2)\)

The balanced chemical equation for this decomposition reaction is: \[ 2Cu(NO_3)_2(s) \rightarrow 2CuO(s) + 4NO_2(g) + O_2(g) \] This reaction demonstrates the breakdown of the nitrate ion into nitrogen dioxide and oxygen, while the copper ions form a stable, solid copper oxide.

The release of nitrogen dioxide and oxygen gas is noticeable due to the brown color of \(NO_2\). The solid left behind, copper(II) oxide, is a black or brown powder, indicating a successful decomposition reaction.

Cupric oxide formation

Cupric oxide, also known as copper(II) oxide, is an important product formed during the decomposition of copper nitrate. This compound is represented by the chemical formula \(CuO\) and appears as a solid with a dark brown or black color. In chemical reactions, it often occurs as one of the end products when copper compounds are heated.

The formation of cupric oxide is significant as it affects both industrial and laboratory processes. It serves as a major component in:

• Catalysts
• Battery electrodes
• Pigments

During the decomposition of copper nitrate, cupric oxide forms as residues settle from a gas-solid reaction. It provides valuable insights into how copper behaves under thermal stress and is an essential tool in metallurgy for purifying copper from its ores. Harvesting this oxide is often a step in refining copper for further use.