Problem 15 - A Complete Resource Book in Chemistry for JEE Main

Question

When strongly heated, orthoboric acid gives (a) \(\mathrm{H}_{2} \mathrm{~B}_{4} \mathrm{O}_{7}\) (b) \(\mathrm{B}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{HBO}_{2}\) (d) \(\mathrm{NaBO}_{2}+\mathrm{B}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

(b) B_2O_3 ight) is formed when orthoboric acid is strongly heated.

Step 1: Understanding the Chemical Reaction

When orthoboric acid (H_3BO_3 ight)) is strongly heated, it undergoes a decomposition reaction. The heat causes it to lose water molecules, resulting in the formation of a new chemical compound.

Step 2: Breaking Down the Decomposition

Initially, orthoboric acid dehydrates to form metaboric acid (HBO_2 ight)). However, upon further heating, additional dehydration occurs, leading to the formation of boron trioxide (B_2O_3 ight)).

Step 3: Chemical Equation of Decomposition

The step-by-step chemical reaction can be summarized as follows: \[ \text{1. } H_3BO_3 \rightarrow HBO_2 + H_2O \quad (\text{formation of metaboric acid}) \\text{2. } HBO_2 \rightarrow B_2O_3 + H_2O \quad (\text{formation of boron trioxide}) \] Hence, the final product of heating orthoboric acid is boron trioxide (B_2O_3 ight)).

Step 4: Identifying the Correct Option

From the possible answers, B_2O_3 ight) is listed as option (b). This means that when orthoboric acid is heated strongly, the correct product formed is boron trioxide, corresponding to option (b).

Key Concepts

Orthoboric Acid

Orthoboric acid, with the chemical formula \( ext{H}_3 ext{BO}_3 \), is a weak acid of boron. It is often found in nature and commonly used in pest control and as an antiseptic.
When orthoboric acid is heated, an interesting chemical transformation occurs. It loses water and begins a decomposition process, transforming into different compounds as the temperature increases.
This process begins with orthoboric acid first forming metaboric acid. Let's explore this fantastic transformation next! Understanding these reactions helps us appreciate how compounds change with conditions, a crucial concept in chemistry.

Boron Trioxide

Boron trioxide is the end product formed when orthoboric acid is heated to high temperatures. It has the chemical formula \( ext{B}_2 ext{O}_3 \) and appears as a white and amorphous solid. It is an important compound in boron chemistry.
Here’s how it forms:

• The initial step in this heating process is the formation of metaboric acid when the orthoboric acid loses water.
• Continuing to heat the metaboric acid causes it to dehydrate further, culminating in the formation of boron trioxide.

This progression highlights the importance of heating and its impact on chemical stability and transformation. Boron trioxide is used industrially in the manufacture of glass and ceramics, indicating its versatility and relevance.

Metaboric Acid

Metaboric acid is an intermediary product in the decomposition of orthoboric acid. It is represented by the chemical formula \( ext{HBO}_2 \).
During heating, orthoboric acid first dehydrates to form metaboric acid. This stage plays a crucial role in the transformation to boron trioxide.

• Metaboric acid is solid and more stable than orthoboric acid at higher temperatures.
• However, it doesn’t remain stable indefinitely. With further heating, it continues to lose water, ultimately ending up as boron trioxide.

Understanding the formation and decomposition of metaboric acid provides insight into chemical reactivity and thermal behavior, essential concepts for students exploring chemical transformations.