Question

Which of the following statement is/are correct for \(\mathrm{H}_{3} \mathrm{BO}_{3} ?\) (1) It has a layer structure in which \(\mathrm{BO}_{3}\) units are joined by hydrogen bonds. (2) It is obtained by treating borax with concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}^{-}\) (3) It is mainly monobasic acid and a Lewis acid. (4) It does not act as a proton donor but acts as an acid by accepting hydroxyl ions. (a) \(1,2,3\) (b) \(2,3,4\) (c) \(1,3,4\) (d) All of these

Short answer

The correct answer is (d) All of these.

Step-by-step solution

Analyze Statement 1

Statement 1 claims that \( \mathrm{H}_3\text{BO}_3 \) has a layer structure where \( \mathrm{BO}_3 \) units are bonded through hydrogen bonds. Boric acid, \( \mathrm{H}_3\text{BO}_3 \), forms sheets with each \( \mathrm{BO}_3 \) unit connected by hydrogen bonds, creating a layered structure. Thus, statement 1 is true.

Analyze Statement 2

Statement 2 claims that \( \mathrm{H}_3\text{BO}_3 \) is obtained when borax reacts with concentrated \( \mathrm{H}_2\text{SO}_4 \). The reaction between borax (\( \mathrm{Na_2B_4O_7} \cdot 10\mathrm{H_2O} \)) and concentrated \( \mathrm{H}_2\text{SO}_4 \) indeed produces boric acid, \( \mathrm{H}_3\text{BO}_3 \). Hence, statement 2 is true.

Analyze Statement 3

Statement 3 claims \( \mathrm{H}_3\text{BO}_3 \) is mainly a monobasic acid and a Lewis acid. In fact, \( \mathrm{H}_3\text{BO}_3 \) behaves as a monobasic acid by accepting \( \mathrm{OH}^- \) ions to form \( \mathrm{[B(OH)_4]^-} \), rather than donating protons. It acts as a Lewis acid because it accepts electrons. Thus, statement 3 is correct.

Analyze Statement 4

Statement 4 states that \( \mathrm{H}_3\text{BO}_3 \) doesn't donate protons but acts as an acid by accepting hydroxyl ions. In solution, \( \mathrm{H}_3\text{BO}_3 \) doesn't donate \( \mathrm{H}^+ \) ions; instead, it accepts \( \mathrm{OH}^- \) to form \( \mathrm{[B(OH)_4]^-} \). Therefore, statement 4 is true.

Conclusion

Since all four statements about \( \mathrm{H}_3\text{BO}_3 \) are correct, the correct option includes all statements. Thus, the answer is option (d) All of these.

Key concepts

Boric Acid

Boric acid, chemically represented as \( \mathrm{H}_3\mathrm{BO}_3 \), is a fascinating compound with unique properties. It is often in the spotlight in chemistry discussions due to its layered structure and its role in creating hydrogen bonds. In its crystalline form, boric acid forms thin sheets where each \( \mathrm{BO}_3 \) unit connects through hydrogen bonds. This structure is crucial to its functionality and adds to its distinctive properties.
When discussing its preparation, boric acid is commonly produced by treating borax (\( \mathrm{Na_2B_4O_7} \cdot 10\mathrm{H_2O} \)) with concentrated sulfuric acid (\( \mathrm{H_2SO_4} \)). This reaction is widely utilized, ensuring the ready availability of boric acid for various uses in labs and industries.
Boric acid's role doesn't stop at its structural and preparatory features; it also plays an essential part in acid-base chemistry. Its ability to accept hydroxyl ions makes it an intriguing player in chemical reactions.

Lewis Acid

A Lewis acid is a compound that can accept a pair of electrons, making it a central concept in acid-base reactions developed by Gilbert N. Lewis. Boric acid \( (\mathrm{H}_3\mathrm{BO}_3) \) is recognized as a Lewis acid due to its electron-accepting ability. Although it doesn’t release protons like traditional Brønsted acids, it accepts \( \mathrm{OH}^- \) ions in solution.
Here’s what makes boric acid a Lewis acid:

• It lacks hydrogen ions to donate as protons, unlike most traditional acids.
• Instead, boric acid accepts \( \mathrm{OH}^- \) ions to form the tetrahydroxyborate ion \( \mathrm{[B(OH)_4]^-} \).

This unique mode of action makes boric acid fundamentally different from typical acids but no less important in the realm of chemistry. Understanding its role as a Lewis acid helps chemists leverage its unique properties in various chemical processes.

Acid-Base Reactions

In the world of chemistry, acid-base reactions reveal much about the fundamental nature of acids and bases. They are reactions where an acid and base neutralize each other, often producing water and a salt. However, not all acid-base reactions fit the classical description. Boric acid's behavior demonstrates this perfectly.
Traditional acid-base theory suggests that acids donate \( \mathrm{H}^+ \) ions, while bases accept them. Boric acid, however, does not behave in this typical Brønsted acid manner. Instead, it accepts \( \mathrm{OH}^- \) ions to form \( \mathrm{[B(OH)_4]^-} \), showing its divergence from regular behaviors.
Key points of boric acid reactions:

• Instead of donating protons, it acts by accepting hydroxide ions.
• This acceptance forms a new ion: \( \mathrm{[B(OH)_4]^-} \).
• This peculiar behavior places boric acid in the realm of Lewis acids rather than Brønsted acids.

Understanding the unique nature of boric acid in acid-base reactions can widen a student's perspective on how diverse and nuanced chemical reactions can be."