Problem 47 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is formed when cupric oxide reacts with glucose? (a) \(\mathrm{CuCHO}\) (b) \(\mathrm{CuO}\) (c) \(\mathrm{Cu}_{2} \mathrm{O}\) (d) \(\mathrm{C}_{5} \mathrm{H}_{11} \mathrm{O}_{6}\)

Step-by-Step Solution

Answer

The product is Cu2O (option c).

Step 1: Understanding the Reaction

When cupric oxide (CuO) reacts with glucose (C6H12O6), it typically undergoes a reduction reaction where cupric oxide loses oxygen to become cuprous oxide (Cu2O). Glucose acts as the reducing agent, and cupric oxide is reduced.

Step 2: Analyzing the Options

Review the options given: (a) CuCHO, (b) CuO, (c) Cu2O, and (d) C5H11O6. Since we are looking for the product of the reduction of CuO, we eliminate options that do not fit this description. Option (b), CuO, is the reactant, not the product, and (d) C5H11O6 relates to the oxidized form of glucose, not the reduction product of copper.

Step 3: Identifying the Correct Product

From our understanding in Step 1, the correct product of the reaction is cuprous oxide (Cu2O). Comparing this with the options, (c) Cu2O is the product formed when cupric oxide is reduced by glucose.

Key Concepts

Reduction Reaction

A reduction reaction involves a chemical process where a substance gains electrons. When cupric oxide (CuO) reacts with glucose, it undergoes a reduction reaction. In this process, cupric oxide, which contains copper in a +2 oxidation state, is reduced to a lower oxidation state. This means it gains electrons and loses oxygen, transforming into cuprous oxide. During this transformation, the energy state of copper is lowered, leading to the formation of new compounds.

An easy way to remember reduction reactions is through the acronym LEO the lion says GER: **L**oss of **E**lectrons is **O**xidation, **G**ain of **E**lectrons is **R**eduction. In this specific reaction, cupric oxide is reduced, demonstrating the principle that when a substance is reduced, its chemical composition is altered by the gain of electrons and the reduction of its oxidation state.

Cuprous Oxide

Cuprous oxide (C_{2}O) is a red or reddish-brown crystalline compound. It is the product formed when cupric oxide reacts with glucose through a reduction reaction. The formula indicates that each molecule consists of two copper atoms and one oxygen atom. This compound is an important result of the reduction process, showcasing the change from a +2 oxidation state to a +1 oxidation state of copper.

Cuprous oxide is not only an attractive chemical for its color but also holds practical uses in various industries:

• It is often used as a pigment.
• It is common in antifouling paints for boats, as it prevents organisms from growing on the hull.
• Cuprous oxide can also be used in the production of certain semiconductor devices.

Its formation is a classic example of how chemical reactions can lead to new material properties and functionalities through changes in atomic arrangements.

Cupric Oxide

Cupric oxide (CuO) acts as the starting material in the reduction reaction with glucose. It is a black solid that features copper in a +2 oxidation state and is a common reagent in chemical reactions. In this process, cupric oxide serves as the oxidizing agent, meaning it provides oxygen to the reaction partner, which is glucose, while gaining electrons itself (being reduced).

The properties of cupric oxide include:

• It is used as a pigment due to its color.
• It functions as a catalyst in organic reactions.
• Cupric oxide is employed in the production of other chemical compounds, such as copper salts.

Its reactive nature makes it an essential player in a variety of chemical transformations, including the one with glucose, where it provides a clear example of a reduction process.

Glucose as Reducing Agent

Glucose (C_{6}H_{12}O_{6}) is widely recognized as a simple sugar found naturally in many plants. In chemical reactions, glucose serves an essential role as a reducing agent, meaning it donates electrons to other substances. In the reaction with cupric oxide, glucose facilitates the reduction of CuO to Cu₂O.

This process happens because glucose itself is oxidized. As glucose donates electrons, it loses its hydrogen atoms, which typically bond with the oxygen atoms that are freed from the reduction of cupric oxide.

• In this reaction, glucose is oxidized to a different compound, often resulting in the formation of gluconic acid or other products.
• As a reducing agent, glucose plays an important role in metabolic processes within organisms, maintaining essential energy sources.

Overall, glucose as a reducing agent highlights its significance not only in chemical reactions but also in biological systems where it is pivotal to life's processes.