Problem 35 - Chemistry and Chemical Reactivity

Question

Write equations for the reactions of aluminum with \(\mathrm{HCl}(\mathrm{aq}), \mathrm{Cl}_{2},\) and \(\mathrm{O}_{2}.\)

Step-by-Step Solution

Answer

Aluminum reacts with HCl to form AlCl3 and H2, with Cl2 to form AlCl3, and with O2 to form Al2O3.

Step 1: Reaction with HCl

Aluminum reacts with hydrochloric acid to produce aluminum chloride and hydrogen gas. The balanced chemical equation for this reaction is: \[2 ext{Al (s)} + 6 ext{HCl (aq)} ightarrow 2 ext{AlCl}_3 ext{(aq)} + 3 ext{H}_2 ext{(g)}.\]

Step 2: Reaction with Cl2

When aluminum reacts with chlorine gas, it forms aluminum chloride. The balanced equation for this synthesis reaction is: \[2 ext{Al (s)} + 3 ext{Cl}_2 ext{(g)} ightarrow 2 ext{AlCl}_3 ext{(s)}.\]

Step 3: Reaction with O2

Aluminum combusts in the presence of oxygen to form aluminum oxide. The balanced chemical equation for this reaction is: \[4 ext{Al (s)} + 3 ext{O}_2 ext{(g)} ightarrow 2 ext{Al}_2 ext{O}_3 ext{(s)}.\]

Key Concepts

Reactions of Aluminum

Aluminum is a versatile element known for its reactive properties, especially with non-metals. When aluminum comes into contact with other substances such as hydrochloric acid, chlorine gas, or oxygen, distinct chemical reactions occur.
Aluminum is highly conductive and lightweight, making it ideal for many applications. In chemical reactions, aluminum often acts as a reducing agent, losing electrons to other atoms.
Let's explore aluminum's interactions, focusing on its reactions with key elements and compounds.

Hydrochloric Acid

Hydrochloric acid (HCl) is a strong acid commonly found in the stomach and used industrially in cleaning and processing materials. When aluminum reacts with hydrochloric acid, an exothermic reaction takes place. This results in the production of aluminum chloride and hydrogen gas.
The balanced equation for this reaction is:

• \[2 \text{Al (s)} + 6 \text{HCl (aq)} \rightarrow 2 \text{AlCl}_3 \text{ (aq)} + 3 \text{H}_2 \text{ (g)}.\]

During the reaction:

• Hydrogen ions from HCl gain electrons from aluminum atoms, releasing hydrogen gas.
• Aluminum ions combine with chloride ions, forming aluminum chloride, a soluble salt.

This reaction exhibits the properties of acids interacting with metals, releasing hydrogen gas.

Chlorine Gas

Chlorine gas (Cl₂) is a greenish-yellow diatomic gas, known for its strong, pungent odor. It's highly reactive, particularly with metals, and forms salts or chlorides in reactions.
When aluminum encounters chlorine gas, a synthesis reaction occurs, creating aluminum chloride. This reaction can be represented by the balanced equation:

• \[2 \text{Al (s)} + 3 \text{Cl}_2 \text{ (g)} \rightarrow 2 \text{AlCl}_3 \text{ (s)}.\]

In this reaction:

• Each aluminum atom donates electrons to chlorine, leading to the formation of aluminum chloride, a solid with strong ionic bonds.
• This is an example of a metal reacting with a halogen, highlighting the tendency of halogens to form halides when reacting with metals.

Aluminum chloride is widely used in various industries, such as in the production of aluminum metal and as a catalyst in chemical reactions.

Oxygen Reaction

Oxygen (\[\text{O}_2\]) is critical for combustion processes and forms oxides by reacting with various elements. When aluminum reacts with oxygen, it forms aluminum oxide, a compound with a protective coating.
The balanced equation for this reaction is:

• \[4 \text{Al (s)} + 3 \text{O}_2 \text{ (g)} \rightarrow 2 \text{Al}_2\text{O}_3 \text{ (s)}.\]

During this reaction:

• Aluminum atoms release electrons, which are gained by oxygen molecules, leading to the formation of aluminum oxide.
• Aluminum oxide is a stable, whitish compound that forms a protective layer on aluminum, preventing further oxidation.

This reaction is an example of combustion in metals, demonstrating the ability of oxygen to support the formation of oxides, an essential concept in understanding both corrosion processes and protective oxidation.