Question

Which of the following is correct statements? (1) Aluminium is a strong oxidizing agent. (2) Aluminium is extracted by the electrolysis of alumina in the presence of cryolite. (3) Aluminium is used in the preparation of duralumin. (4) Aluminium liberates hydrogen on treating with a base. (a) \(1,2,3\) (b) \(2,3,4\) (c) \(1,3,4\) (d) 2,4

Short answer

The correct option is (b) \(2,3,4\).

Step-by-step solution

Analyzing Statement 1

Aluminium is not a strong oxidizing agent. In fact, it is a reducing agent due to its tendency to lose electrons easily. Hence, statement 1 is incorrect.

Evaluating Statement 2

Aluminium is extracted by the Hall-Héroult process, which involves the electrolysis of alumina (Al_2O_3) dissolved in molten cryolite (Na_3AlF_6). This lowers the melting point of alumina and increases conductivity. Therefore, statement 2 is correct.

Assessing Statement 3

Duralumin is an alloy that contains aluminium as its major component, combined with small amounts of copper, manganese, and magnesium. Aluminium is indeed used in the preparation of duralumin, so statement 3 is correct.

Investigating Statement 4

When aluminium reacts with a base like sodium hydroxide (NaOH), it forms sodium aluminate (NaAlO_2) and releases hydrogen gas. This means statement 4 is correct.

Determine the Correct Answer

Based on the evaluation, statements 2, 3, and 4 are correct. Thus, the correct option is (b) \(2,3,4\).

Key concepts

Electrolysis of Alumina

Aluminium is primarily extracted through a process known as the Hall-Héroult process, which involves the electrolysis of alumina ( Al_2O_3 ). Electrolysis is a technique used to drive a chemical reaction using electricity. In this context, alumina is dissolved in molten cryolite ( Na_3AlF_6 ), which serves two essential purposes: reducing the melting point of alumina and improving its conductivity. Cryolite acts as a solvent that facilitates the production of aluminium by lowering the temperature required for the electrolytic process, making it more energy-efficient.
During electrolysis, electric current passes through the molten mixture, causing alumina to decompose into aluminium and oxygen. Aluminium ions gain electrons, turning into pure aluminium, which collects at the bottom of the cell, while oxygen ions form oxygen gas at the anode, which is usually made of carbon. This process is highly effective in obtaining pure aluminium metal from its ore and is heavily used industrially to produce aluminium due to its cost and energy efficiency.
Understanding the electrolysis of alumina is crucial in the field of metallurgy, especially as aluminium is utilized in numerous applications due to its lightweight and corrosion resistance.

Duralumin Alloy

Duralumin is a versatile alloy primarily composed of aluminium. It is made by mixing aluminium with other elements such as copper, manganese, and magnesium. This alloy is renowned for its enhanced strength and lightweight properties, making it highly valuable in the aerospace and automotive industries.
Here are some characteristics and uses of duralumin that highlight its importance:

• Strength: The addition of copper and other metals significantly increases the tensile strength of aluminium, meaning duralumin can withstand greater stresses compared to pure aluminium.
• Lightweight: Despite its increased strength, duralumin maintains a low density, which is critical in applications where weight is a factor, such as aircraft manufacturing.
• Corrosion Resistance: By including specific elements, duralumin exhibits better resistance to corrosion than its constituent metals alone.
• Machinability: Duralumin is relatively easy to work with and shape, making it an ideal material for various manufacturing processes.

Overall, the development and utilization of duralumin expanded the possibilities in areas where materials need to balance strength, weight, and durability, offering a competitive edge over traditional metals.

Reactivity with Bases

Aluminium exhibits interesting chemical behavior when it comes into contact with bases. A common reaction involves aluminium and sodium hydroxide (NaOH). In this reaction, aluminium reacts with the base to produce sodium aluminate (NaAlO_2) and hydrogen gas. This is represented by the following equation:\[2Al + 2NaOH + 6H_2O \rightarrow 2NaAlO_2 + 3H_2\]
This reaction is notable because not many metals react with bases. The production of hydrogen gas during this reaction is visible as bubbling or effervescence at the site of the reaction, representing an active chemical process.
Aluminium's ability to react with bases arises from its amphoteric nature, meaning it can react with both acids and bases. This makes it a useful metal in various chemical processes and industrial applications, such as wastewater treatment and hydrogen production. Recognizing how aluminium interacts with bases provides insights into its chemical versatility and the breadth of its applications in industry.