Question

The composition of diaspore is (a) \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot 3 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (d) \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot 2 \mathrm{H}_{2} \mathrm{O}\)

Short answer

The composition of diaspore is (b) \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot \mathrm{H}_{2} \mathrm{O}\).

Step-by-step solution

Understanding the Problem

We need to determine the correct chemical composition of diaspore, which is an important mineral for aluminum extraction. Identify the correct chemical formula from the given options.

Review of Options

Evaluate each given option: (a) \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot 3 \mathrm{H}_{2} \mathrm{O}\) is the composition of a hydrated alumina, often known as gibbsite. (b) \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot \mathrm{H}_{2} \mathrm{O}\) suggests a monohydrate form of alumina, indicating diaspore. (c) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is simply alumina, also known as corundum. (d) \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) resembles another hydrated alumina, usually boehmite.

Application of Knowledge

Diaspore is known as an aluminum oxyhydroxide mineral, which means it consists of aluminum, oxygen, and one molecule of water (or hydroxide). Therefore, the formula closely matching this definition is option (b): \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot \mathrm{H}_{2} \mathrm{O}\).

Conclusion

The composition of diaspore is correctly represented by option (b), \(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot \mathrm{H}_{2} \mathrm{O}\), as diaspore is an aluminum monohydrate.

Key concepts

Aluminum extraction

Aluminum extraction is a crucial industrial process that transforms bauxite ore into pure aluminum metal. Bauxite is rich in aluminum-bearing minerals like gibbsite, boehmite, and diaspore. These minerals are vital because they contain the aluminum oxide needed for aluminum production.

The extraction process begins by mining bauxite, which is then purified using the Bayer process. This involves crushing the bauxite and treating it with caustic soda, which dissolves the alumina (or aluminum oxide) into a solution. After filtration, impurities are removed, and the solution is cooled to precipitate hydrated alumina.

It is important to note that the three hydrated aluminas—gibbsite, boehmite, and diaspore—have different water content. This impacts their solubility and thus extraction efficiency, with gibbsite being the easiest to process due to its higher water content. The Bayer process makes gibbsite dissolve easily; however, boehmite and diaspore require higher temperatures. Understanding these differences is key for efficient extraction.

• Gibbsite is processed at lower temperatures.
• Boehmite and diaspore require higher temperatures.
• Impurities are filtered out during extraction.

Hydrated alumina

Hydrated alumina refers to aluminum oxides that have chemically bonded water molecules. This includes minerals like gibbsite, boehmite, and diaspore, each with different levels of hydration. These variations significantly affect their properties and how they dissolve during the extraction process.

A common characteristic of hydrated alumina is that they're typically more reactive than their dehydrated counterparts. For example, gibbsite's composition is \[ \mathrm{Al}_{2}\mathrm{O}_{3} \cdot 3\mathrm{H}_{2}\mathrm{O} \] meaning it has three water molecules attached, which makes it an advantageous source for aluminum extraction. Similarly, **diaspore**, with the formula \[ \mathrm{Al}_{2}\mathrm{O}_{3} \cdot \mathrm{H}_{2}\mathrm{O} \] has a distinct water molecule configuration influencing its solubility.

Understanding the chemistry of hydrated aluminas is essential across various applications beyond extraction, such as in ceramics and chemical industries. They provide flexibility in processes due to their ease of conversion from solid to solution forms, a property utilized for producing fine alumina powder used in refractory materials.

Chemical formulas

Chemical formulas are symbolic representations of chemical compounds, showing the elements present and their ratios. In the context of minerals like diaspore or gibbsite, their formulas not only define their composition but also give insights into their chemical properties and extraction pathways.

For instance, the formula \[ \mathrm{Al}_{2} \mathrm{O}_{3} \cdot \mathrm{H}_{2} \mathrm{O} \] indicates diaspore's composition as aluminum oxide with one water molecule. This formula is crucial for understanding its behavior during heating and extraction processes, given the role of the hydroxide in forming aluminum in the Bayer process.

Similarly, formulas like \[ \mathrm{Al}_{2} \mathrm{O}_{3} \cdot 3\mathrm{H}_{2}\mathrm{O} \] for gibbsite or \[ \mathrm{Al}_{2} \mathrm{O}_{3} \cdot 2\mathrm{H}_{2} \mathrm{O} \] for boehmite, denote different hydration levels, influencing reactivity and process suitability.

Recognition of these formulas assists in predicting material behavior under various conditions, allowing chemists and engineers to tailor processes efficiently, especially in metallurgy and material science industries.