Question

Which of the following is correct? (1) Al reacts with \(\mathrm{NaOH}\) and liberate \(\mathrm{H}_{2}\) (2) \(\mathrm{AlCl}_{3}\) is a Lewis acid. (3) Al is used in the manufacture of electrical cables. (4) \(\mathrm{NaOH}\) is used during Halls process of purification of bauxite. (a) \(1,2,3\) (b) 2,3 (c) \(2,3,4\) (d) \(1,2,3,4\)

Short answer

The correct option is (d) 1, 2, 3, 4.

Step-by-step solution

Analyze Statement 1

Aluminum (Al) reacts with sodium hydroxide (NaOH) to produce hydrogen gas (H2) and sodium aluminate (NaAlO2). The reaction can be represented as follows: \[ 2Al + 2NaOH + 2H_2O \rightarrow 2NaAlO_2 + 3H_2 \] This statement is correct as the reaction liberates hydrogen gas.

Analyze Statement 2

Aluminum chloride (\(\mathrm{AlCl}_{3}\)) acts as a Lewis acid because it can accept electron pairs due to its electron-deficient central aluminum atom, which does not have a complete octet. Thus, this statement is correct.

Analyze Statement 3

Aluminum is a good conductor of electricity and is lightweight and flexible, making it suitable for the manufacture of electrical cables. Therefore, this statement is correct.

Analyze Statement 4

In the Hall's process, bauxite, which is aluminum ore, is purified using NaOH to dissolve the alumina, leaving behind impurities. This purification step is part of the Bayer process, which is a precursor to Hall's process. Hence, this statement is also correct.

Determine the Correct Option

After analyzing each statement, we see that all four statements are correct. Therefore, the correct option is (d) \(1,2,3,4\).

Key concepts

Aluminium reactions

Aluminium is an interesting element when it comes to chemical reactions. Its ability to react with different substances demonstrates its versatile nature in chemistry. A classic reaction involves aluminium (Al) and sodium hydroxide ( aOH). When these two substances react, aluminium essentially swaps its electrons to form sodium aluminate ( 1aAlO_2) and hydrogen gas ( 1H_2). This can be represented by the chemical equation: \[ 2Al + 2NaOH + 2H_2O \rightarrow 2NaAlO_2 + 3H_2 \]This reaction is fascinating for a few reasons:

• It shows aluminium as an active metal able to donate electrons.
• Hydrogen gas is released, which is quite flammable and needs careful handling.
• The formation of sodium aluminate is crucial in various industrial applications.

Understanding aluminium reactions like this one helps us comprehend its practical applications and its role as a key industrial element.

Lewis acid

A Lewis acid is an intriguing concept in chemistry, highlighted by compounds like aluminium chloride ( 2aCl_3). A Lewis acid is a compound that can accept a pair of electrons from a donor, called a Lewis base. Why is 2aCl_3 a Lewis acid? This ties back to aluminium's electronic configuration. In 2aCl_3, the central aluminium atom is short of a full octet; it holds only 6 electrons. This electron deficiency makes it eager to accept more electrons, thereby acting as a Lewis acid.
Its willingness to accept electron pairs makes 2aCl_3 an important reagent in chemical reactions, especially in organic chemistry. It can, for instance, help catalyze certain reactions by forming temporary complexes with bases. Recognizing 2aCl_3 as a Lewis acid helps us appreciate its broad application in chemical processes.

Electrical cable materials

Aluminium's role in electrical wiring is quite profound due to its excellent properties as a metal. While copper is commonly known in electrical applications, aluminium is also widely used for several reasons:

• Conductivity: Aluminium conducts electricity efficiently. Though not as conductive as copper, it's still ample for power distribution.
• Lightweight: It's significantly lighter than copper. This property becomes advantageous in overhead power lines where weight is a considerable concern.
• Flexibility: Aluminium is flexible, making it easier to work with and install.
• Cost-effective: It is generally more economical compared to copper, making it a practical choice for large-scale projects.

These attributes render aluminium a vital component in the manufacturing of electrical cables, aiding in efficient power transmission around the world.

Bauxite purification processes

The purification of bauxite is a key step in producing aluminium, and understanding this process unveils the intricate art of extraction metallurgy. Bauxite, the primary ore for aluminium, contains alumina (Al_2O_3), which is what we need to extract. The process begins often using sodium hydroxide in what is called the Bayer process. Here's a simplified view:

• Dissolution: Crushed bauxite is mixed with NaOH, dissolving the alumina, a process called digestion.
• Separation: The remaining insoluble impurities, or "red mud," are separated.
• Precipitation: Alumina is precipitated from the solution.

Further treatment in the Hall process eventually turns this purified alumina into metallic aluminium. The interplay between these two processes highlights how chemistry enables us to go from raw bauxite to the shiny aluminium we use daily.