Question

What is not a appropriate method for the isolation of elemental boron? (a) Electrolytic reduction of aqueous \(\mathrm{B}(\mathrm{OH})_{3}\). (b) Refluxing borax with sodium peroxide. (c) High temperature reduction of \(\mathrm{B}_{2} \mathrm{O}_{3}\) with magnesium. (d) High temperature reduction of \(\mathrm{BBr}_{3}\) with hydrogen over a Ta wire.

Short answer

Option (a) is not a suitable method for isolating elemental boron.

Step-by-step solution

Analyze Option (a)

Option (a) proposes the electrolytic reduction of aqueous \(\mathrm{B}(\mathrm{OH})_{3}\). Electrolysis of aqueous solutions generally works for metals and not for metalloids like boron. Boron is not typically isolated using this method.

Evaluate Option (b)

Option (b) suggests refluxing borax with sodium peroxide. This process is used to convert sodium perborate to borax in chemical reactions, primarily for different compounds, but not specifically for isolating elemental boron.

Review Option (c)

Option (c) involves the high-temperature reduction of \(\mathrm{B}_{2} \mathrm{O}_{3}\) with magnesium. This is a known method for reducing boron oxide to obtain elemental boron.

Consider Option (d)

Option (d) uses high-temperature reduction of \(\mathrm{BBr}_{3}\) with hydrogen over a Ta wire. This is a method used to obtain boron via the decomposition of \(\mathrm{BBr}_{3}\) in a hydrogen atmosphere, therefore, it is appropriate for isolating elemental boron.

Determine the Incorrect Method

Comparing all options, Option (a), the electrolytic reduction of aqueous \(\mathrm{B}(\mathrm{OH})_{3}\), is not a suitable method for the isolation of elemental boron as opposed to the other methods listed.

Key concepts

Electrolytic Reduction

Electrolytic reduction is a method commonly used to reduce metal ions and obtain pure metals by passing electric current through an electrolyte solution. This technique is suitable for elements that can form stable ions in aqueous solution. However, when it comes to metalloids like boron, this process does not work effectively.

Boron is a non-metallic element with properties of a metalloid. It forms complex compounds rather than simple ions in aqueous solutions, which makes electrolytic processes inefficient for its reduction. Therefore, attempting to isolate boron via electrolytic reduction of its aqueous form, such as \(B(OH)_3\), would not yield the desired pure elemental form of boron. In the context of isolating boron, alternative methods are more suitable.

High Temperature Reduction

High temperature reduction is an effective method for isolating boron from its compounds. This process typically involves heating boron oxide (\( B_2O_3 \)) with a reducing agent, such as magnesium, at very high temperatures. The chemical reactions occurring during this process strip oxygen from the boron compound, leaving elemental boron as a result.

This method takes advantage of the fact that boron oxides can be broken down at high temperatures, and a stronger reducing agent can facilitate the isolation. Because boron has a high melting point and complex chemical behavior, high temperature reduction with magnesium or similar agents effectively isolates elemental boron. Such methods are generally consistent, making them a practical choice for producing boron in its purest form.

Metalloid Isolation Methods

Isolating metalloids like boron requires specialized techniques due to their unique properties, which lie between metals and non-metals. Metalloids do not form basic oxides like metals, nor do they form acidic oxides like non-metals, making standard isolation methods less applicable.

Common metalloid isolation methods include high temperature reduction and thermal decomposition of volatile compounds under specific conditions. For example, reducing \( BBr_3 \) with hydrogen involves high temperatures and possibly a catalyst like a Ta wire to achieve the decomposition required for isolating boron.

• Combining heat with specific reducing conditions aids in breaking bonds in the boron compounds and accumulating pure boron as a product.
• These processes are crucial where simple electrolytic or acid-based reactions would fail due to the complex chemistry of metalloids.

Overall, understanding these nuanced methods helps in achieving the successful isolation of boron, exploring its versatile uses in technology and various industries.