Problem 115 - A Complete Resource Book in Chemistry for JEE Main

Question

Borax is converted into B by following steps Borax \(\stackrel{\mathrm{A}}{\longrightarrow} \mathrm{H}_{3} \mathrm{BO}_{3} \stackrel{\Delta}{\longrightarrow} \mathrm{B}_{2} \mathrm{O}_{3} \quad \mathrm{~B} \stackrel{\mathrm{B}}{\longrightarrow}\) Product Reagents \(\mathrm{A}\) and \(\mathrm{B}\) are (a) acid, \(\mathrm{Fe}\) (b) acid, \(\mathrm{Mg}\) (c) acid, \(\mathrm{Sn}\) (d) acid, Al

Step-by-Step Solution

Answer

The correct reagents are (b) acid, Mg.

Step 1: Understand the Reaction Sequence

First, observe the given sequence of reactions: Borax is converted to \( H_3BO_3 \), then to \( B_2O_3 \), and eventually to \( B \) (Boron). Borax (\( Na_2B_4O_7 \)) is typically converted to Boric Acid (\( H_3BO_3 \)) using an acid.

Step 2: First Conversion

The conversion of borax (\( Na_2B_4O_7 \)) to Boric Acid (\( H_3BO_3 \)) is achieved using hydrochloric or another acid. So the reagent \( A \) is an acid. This eliminates choices that don't start with 'acid'.

Step 3: Convert \( H_3BO_3 \) to \( B_2O_3 \)

Upon heating (indicated by \( \Delta \)), Boric Acid (\( H_3BO_3 \)) converts to Boron trioxide (\( B_2O_3 \)).

Step 4: Reduction to Boron

To obtain Boron from Boron trioxide (\( B_2O_3 \)), a reducing agent is needed. Common reducing agents for Boron production are metals like magnesium (Mg), which reacts with \( B_2O_3 \) to produce elemental Boron and magnesium oxide (\( MgO \)). Thus, reagent \( B \) is \( Mg \).

Step 5: Finalize and Match Choices

The reaction sequence involves using an acid to convert Borax to Boric Acid, then with \( Mg \) to reduce the boron oxide to Boron. The correct option that involves both 'acid' and 'Magnesium' is (b) acid, \( Mg \).

Key Concepts

Boron

Boron is a fascinating element that belongs to the metalloid family in the periodic table. It is unique because it exhibits properties of both metals and non-metals. Boron is essential to various industrial processes, largely due to its ability to form stable covalent bonds.

It naturally occurs in the environment in compounds like Borax and Boric Acid. One of Boron's notable properties is its hardness and high melting point, which makes it useful in materials that need to withstand extreme conditions. The most common natural source of Boron is Borax (\( Na_2B_4O_7 \)), a white crystalline compound.

In chemistry, Boron is critical for the synthesis of numerous boron-containing compounds. Its chemistry is vast, extending into fields such as agriculture, where boron compounds improve plant growth, and in medicine, as it has potential therapeutic effects.

Reduction Reactions

Reduction reactions play a crucial role in converting compounds to extract specific elements, such as Boron from Boron trioxide (\( B_2O_3 \)). Reduction is a fundamental chemical process where a molecule, ion, or atom decreases its oxidation state, usually by gaining electrons.

A classic method to obtain pure Boron from Boron trioxide involves the use of a metal reducing agent. Common metals used in reduction reactions include magnesium (\( Mg \)), aluminum (\( Al \)), and lithium (\( Li \)). In the Boron extraction process, magnesium acts as the reducing agent in the following simplified reaction:

• \( B_2O_3 + 3Mg \rightarrow 2B + 3MgO \)

This reaction illustrates how magnesium donates electrons to Boron trioxide, freeing boron atoms and forming magnesium oxide as a byproduct. Reduction reactions are widespread in chemistry due to their ability to produce pure elements and fine-tune materials' properties.

Boric Acid Conversion

Boric Acid conversion is an essential process in boron chemistry. It begins with Borax (\( Na_2B_4O_7 \)), which is converted to Boric Acid (\( H_3BO_3 \)) using an acid like hydrochloric or sulfuric acid. This step is significant because Boric Acid is a key precursor for producing other boron-based compounds.

Once Boric Acid (\( H_3BO_3 \)) is formed, it can be further converted into Boron trioxide (\( B_2O_3 \)) by heating. This step is indicated by the symbol \( \Delta \), representing heat in chemical equations. The conversion is straightforward and can be expressed as follows:

• \( 2H_3BO_3 \rightarrow B_2O_3 + 3H_2O \)

This reaction removes water and leaves behind Boron trioxide. Following this step, Boron trioxide can be reduced to elemental boron through the reduction reactions previously discussed, completing the pathway from Borax to pure Boron.