Question

Heating an aqueous solution of aluminium chloride to dryness will give (a) \(\mathrm{AlCl}_{3}\) (b) \(\mathrm{Al}_{2} \mathrm{Cl}_{3}\) (c) \(\mathrm{Al}(\mathrm{OH}) \mathrm{Cl}_{2}\) (d) \(\mathrm{Al}_{2} \mathrm{Cl}_{6}\)

Short answer

The solution will give \\(\mathrm{Al}_2\mathrm{Cl}_6\\) upon drying, so option (d) is correct.

Step-by-step solution

Understanding the Chemical Process

When heating an aqueous solution of aluminium chloride, the water is removed, and the aluminium chloride transitions to a solid form upon drying. In its solid form, aluminium chloride, \(\mathrm{AlCl}_3\), forms a crystalline structure of dimers under typical conditions.

Identify the Form in which Aluminium Chloride Exists in Solid State

Aluminium chloride in solid state exists predominantly as a dimer, \(\mathrm{Al}_2\mathrm{Cl}_6\), especially at room temperature. The monomer \(\mathrm{AlCl}_3\) primarily exists in gaseous form but forms dimers on cooling or in the solid state.

Connecting Chemical Process to Options

The problem asks what form aluminium chloride will take after being heated to dryness from an aqueous solution. Since drying results in the crystalline form, the most stable solid form is \(\mathrm{Al}_2\mathrm{Cl}_6\). This corresponds to option (d).

Confirming the Correct Answer

Upon heating and drying, aluminium chloride transitions to its most stable form at room temperature, which is \(\mathrm{Al}_2\mathrm{Cl}_6\). This confirms option (d) is correct for the solid form obtained.

Key concepts

Chemical Process

The term "chemical process" refers to a series of actions or steps taken to convert one or more substances into different substances. In the context of the exercise, when you heat an aqueous solution of aluminium chloride, a chemical process occurs.

During this process, the water in the solution evaporates due to the heat. This evaporation leaves behind the aluminium chloride in a different state. The transition from a liquid solution to a solid form is a key part of this chemical process.

• Evaporation removes water from the solution.
• Solid aluminium chloride remains as a result.

This transformation emphasizes the importance of understanding how substances change state under different conditions, such as temperature.

Aqueous Solution

An aqueous solution consists of a substance dissolved in water. In our case, aluminium chloride is dissolved in water to form an aqueous solution.

These solutions are significant in chemical reactions because they allow substances to interact in ways not possible in their solid state. The ions separate in the solution, leading to increased reactivity.

• Aluminium chloride dissolves in water, separating into ions.
• These ions interact more freely and undergo reactions when water is removed.

Understanding how solutions form and behave is crucial for predicting the outcomes of chemical processes like the one described in the exercise.

Crystalline Structure

When substances transition to a solid state from a solution, they often arrange themselves into ordered structures known as crystalline structures. For aluminium chloride, this means it doesn't exist as single AlCl3 molecules but rather as Al2Cl6 dimers.

The crystalline structure is stable because it minimizes energy, aligning molecules in a regular pattern that balances forces. This arrangement is especially true for aluminium chloride when it solidifies from a liquid state.

• Formation of dimers like Al2Cl6 shows the regular, repeating pattern essential in crystalline structures.
• This stable form is thermodynamically favorable.

Knowing the stable forms substances take is vital for understanding their physical properties and behavior upon changes like heating.

Solid State

The solid state of a material is characterized by its definite shape and volume, whereas liquids and gases conform to the container's shape. When aluminium chloride is heated from an aqueous solution to reach the solid state, it establishes a stable dimer form, Al2Cl6.

In this state, the molecules are tightly packed, maintaining a fixed position and interacting strongly with neighboring molecules. This rigidity gives the solid its characteristic shape and structure, unlike liquids or gases.

• Aluminium chloride solidifies into a dimer form.
• This has implications for both physical stability and reactivity.

By understanding the solid state, one can predict how aluminium chloride behaves in various environmental conditions, including temperature changes.