Question

Thermite is a mixture of iron oxide and (a) aluminium powder (b) zinc powder (c) iron turnings (d) copper turnings.

Short answer

The correct answer is (a) aluminium powder.

Step-by-step solution

Understanding the Composition of Thermite

Thermite is composed of a metal oxide and a reducing agent. It is a pyrotechnic composition that, when ignited, produces an exothermic reduction-oxidation (redox) reaction known as a thermite reaction. The metal oxide is generally iron(III) oxide.

Identifying the Reducing Agent in Thermite

The reducing agent in a thermite reaction should be a metal that can reduce the iron(III) oxide to iron. This metal must be more reactive in order to donate electrons to the iron(III) oxide. Among the options given, aluminium is known for being an effective reducing agent in thermite reactions due to its high reaction enthalpy.

Choosing the Correct Answer

Knowing that aluminium is a reactive metal capable of reducing iron(III) oxide to molten iron in the thermite reaction, we can deduce that the right answer among the provided options is aluminium powder.

Key concepts

Iron Oxide in the Thermite Reaction

Iron oxide plays a critical role in the thermite reaction. In this exothermic process, iron(III) oxide, also known as ferric oxide, reacts with another metal to produce molten iron and metal oxide. The reaction's charm lies in its ability to produce a high degree of heat, enough to melt the iron.

Iron oxide is preferred in the thermite reaction because of its stability and availability. It provides the oxygen necessary for the reaction, acting as an oxidizing agent. When choosing materials for the thermite reaction, iron oxide's purity and particle size can significantly influence the reaction's vigor and temperature.

Aluminium Powder as a Fuel Source

Aluminium powder, commonly used as a fuel source in the thermite reaction, offers a high energy yield due to its potent reducing properties. Once ignited, aluminium powder undergoes an exothermic reaction with iron oxide, transferring electrons and reducing the iron oxide to iron.

Its effectiveness is attributed to the fact that aluminium is a highly reactive metal, with a strong affinity for oxygen. This renders it a perfect candidate to act as a reducing agent in thermite reactions, outshining other metals in terms of reactivity and heat release.

Understanding Reducing Agents

In chemical reactions, a reducing agent is a substance that donates electrons to another reactant, thus bringing about reduction. Reducing agents are integral to redox reactions; they undergo oxidation themselves while reducing another substance.

In the context of the thermite reaction, the reducing agent should be a metal that can readily lose electrons to reduce the iron oxide to pure iron. This agent is pivotal because it determines both the efficacy and the intensity of the reaction. Metals with a more negative standard reduction potential than iron serve well as reducing agents because they can easily donate electrons in this highly exothermic process.

Redox Reaction Mechanism

A redox reaction is a chemical reaction involving the transfer of electrons between two substances — an oxidizing agent and a reducing agent. In a thermite reaction, which is a type of redox reaction, the iron oxide serves as the oxidizing agent, and the aluminium powder acts as the reducing agent.

This transfer of electrons triggers a profound energy release in the form of heat and light. The process results in a molten metal, typically iron, and a new metal oxide formed from the reducing agent. Understanding the mechanism of redox reactions is critical for grasping the principles behind the thermite reaction and its practical applications, including welding and metal cutting.