Problem 14 - A Complete Resource Book in Chemistry for JEE Main

Question

Mark the wrong statement which of the following statements about/regarding \(\mathrm{BF}_{3}\) is incorrect? (a) it forms an addition compound with \(\mathrm{NH}_{3}\) (b) it is a volatile liquid at room temperature (c) it combines with either to form boron trifluoride etherate (d) it acts as a Lewis acid

Step-by-Step Solution

Answer

Statement (b) is incorrect; \( \mathrm{BF}_3 \) is a gas at room temperature.

Step 1: Understanding the Question

We need to identify the incorrect statement regarding the chemical compound \( \mathrm{BF}_3 \). We will examine each statement (a, b, c, and d) to see if it's true or false.

Step 2: Evaluating Statement (a)

Statement (a) says \( \mathrm{BF}_3 \) forms an addition compound with \( \mathrm{NH}_3 \). Since \( \mathrm{BF}_3 \) acts as a Lewis acid and \( \mathrm{NH}_3 \) acts as a Lewis base, they can form an addition compound known as \( \mathrm{BF}_3\cdot\mathrm{NH}_3 \). This statement is true.

Step 3: Evaluating Statement (b)

Statement (b) claims \( \mathrm{BF}_3 \) is a volatile liquid at room temperature. In fact, \( \mathrm{BF}_3 \) is not a liquid but a gas at room temperature. Therefore, this statement is incorrect.

Step 4: Evaluating Statement (c)

Statement (c) indicates that \( \mathrm{BF}_3 \) combines with ether to form boron trifluoride etherate. This is true, as \( \mathrm{BF}_3 \) can coordinate with ethers to create addition compounds like \( \mathrm{BF}_3\cdot\text{ether} \).

Step 5: Evaluating Statement (d)

Statement (d) asserts that \( \mathrm{BF}_3 \) acts as a Lewis acid. Given that \( \mathrm{BF}_3 \) accepts electron pairs from Lewis bases, it indeed acts as a Lewis acid. This statement is true.

Key Concepts

Boron Trifluoride

Boron trifluoride, expressed with the chemical formula \( \mathrm{BF}_3 \), is an interesting compound known for its unique properties. BF₃ is a chemical compound composed of one boron atom and three fluorine atoms. At room temperature, boron trifluoride is a colorless gas rather than a liquid, which is an important distinction.
This gas plays a significant role in various chemical applications due to its reactivity and its ability to form stable compounds with other substances. Its significance is enhanced by its role as a Lewis acid, which we will explore further in the following sections. Additionally, boron trifluoride easily forms complex compounds due to its electron-deficient boron atom, allowing it to interact particularly with Lewis bases like ammonia and ethers.

Lewis Acid

A Lewis acid is a chemical species that can accept an electron pair. Boron trifluoride (\( \mathrm{BF}_3 \)) is a classic example of a Lewis acid. This quality is due to the electron deficiency of the boron atom in BF₃. By having an incomplete octet, the boron atom eagerly seeks electron pairs to achieve a more stable electron configuration.
The functionality of Lewis acids is not just theoretical, but practical. They are often used as catalysts in organic reactions. In the presence of Lewis bases, which donate electron pairs, Lewis acids form adducts like \( \mathrm{BF}_3 \cdot \mathrm{NH}_3 \).
This aspect of \( \mathrm{BF}_3 \) as a Lewis acid is important because it determines how it interacts with other molecules, making it indispensable in chemical synthesis and coordination chemistry.

Volatility

Volatility refers to how easily a substance turns from a liquid or solid into a vapor. In the context of boron trifluoride, it is crucial to recognize that it is a gas at room temperature, not a liquid. This fundamental property affects how BF₃ is stored and handled in chemical processes.
The high volatility of \( \mathrm{BF}_3 \) requires careful containment, as it can disperse easily in the air due to its gaseous state at room temperatures. Moreover, as a reactive gas, \( \mathrm{BF}_3 \) must be managed to prevent accidental exposure or reactions with other substances. This highlights the importance of understanding the physical states and properties of chemicals used in the laboratory and industrial settings.

Ammonia Reaction

The reaction between boron trifluoride (\( \mathrm{BF}_3 \)) and ammonia (\( \mathrm{NH}_3 \)) is a prime example of a Lewis acid-base interaction. In this reaction, \( \mathrm{BF}_3 \) acts as the Lewis acid, while \( \mathrm{NH}_3 \) serves as the Lewis base.
Ammonia, a compound with a lone pair of electrons on the nitrogen atom, readily donates this pair to \( \mathrm{BF}_3 \). This results in the formation of a stable adduct, noted as \( \mathrm{BF}_3 \cdot \mathrm{NH}_3 \). This reaction showcases the electron pair transfer characteristic of Lewis acid-base theory, and is an essential concept in understanding chemical bonding.
The resultant compound changes the properties of the individual reactants, illustrating the significance of chemical reactions in modifying compound characteristics and in various industrial applications.