Question

Write reactions to justify amphoteric nature of aluminium.

Short answer

Aluminium can react with acids (e.g., HCl) and bases (e.g., NaOH), showing its amphoteric nature.

Step-by-step solution

Define Amphoteric Nature

An amphoteric substance can react with both acids and bases. In this case, we need to demonstrate that aluminium can behave as both a base and an acid.

Reaction with Acid

When aluminium reacts with hydrochloric acid ( Al + 3HCl → AlCl_3 + 3/2 H_2). This reaction shows aluminium behaving as a base, reacting with an acid to form a salt and hydrogen gas.

Reaction with Base

When aluminium reacts with a strong base like sodium hydroxide, it forms sodium aluminate and hydrogen gas ( 2Al + 6NaOH + 6H_2O → 2Na_3Al(OH)_6 + 3H_2). Here, aluminium reacts with a base, showing its ability to behave as an acid in the presence of a stronger base.

Conclude Amphoteric Behavior

From the reactions shown in Steps 2 and 3, we conclude that aluminium can react with both acids and bases, substantiating its amphoteric nature.

Key concepts

Aluminium Reactions

Aluminium is a remarkable element due to its ability to react with both acids and bases, demonstrating its amphoteric nature. This characteristic means that it can behave either as an acid or a base depending on the surroundings. Understanding aluminium's reactions is essential, as it is widely used in industries and plays a significant role in various chemical processes.
One of the classic reactions showcasing aluminium's versatility is its interaction with acids and bases. These reactions not only demonstrate aluminium's dual behavior but also produce products useful in numerous applications. This dual behavior is mostly due to the presence of oxides and hydroxides on the aluminium surface that can easily participate in chemical reactions with both acids and bases.

Reaction with Acid

When aluminium comes into contact with an acid, it relinquishes electrons, enters a chemical reaction, and forms salt and hydrogen gas as products. A typical reaction is when aluminium reacts with hydrochloric acid (HCl).

• The chemical equation for this reaction is: \[ \text{2Al} + \text{6HCl} \rightarrow \text{2AlCl}_3 + \text{3H}_2 \]
• In this reaction, aluminium behaves as a base, accepting protons from the acid.
• The end products are aluminium chloride (\(\text{AlCl}_3\)) and hydrogen gas (\(\text{H}_2\)).

This reaction is a clear display of aluminium's ability to neutralize an acid, showcasing its practical amphoteric nature. The reaction also releases hydrogen gas, a substance often collected for various industrial applications.

Reaction with Base

Aluminium's amphoteric characteristics are demonstrated further when it reacts with a base. In the presence of a strong base like sodium hydroxide (NaOH), aluminium behaves like an acid.

• When aluminium reacts with a base, the chemical equation can be written as: \[ \text{2Al} + \text{6NaOH} + \text{6H}_2\text{O} \rightarrow \text{2Na}_3\text{Al(OH)}_6 + \text{3H}_2 \]
• In this reaction, aluminium gives up hydroxide ions to the base and forms sodium aluminate (\(\text{Na}_3\text{Al(OH)}_6\)).

The reaction with a base highlights aluminium's ability to act as a donor of hydroxide ions and behave like an acid. Like the acid reaction, hydrogen gas is also released, making this reaction valuable for certain industrial manufacturers.