Problem 13 - 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.

Step 1: Analyze Statement (a)

Statement (a) claims that \( \mathrm{BF}_{3} \) forms an addition compound with \( \mathrm{NH}_{3} \). This is a true statement because \( \mathrm{BF}_{3} \), a Lewis acid, can accept a pair of electrons from the nitrogen atom in \( \mathrm{NH}_{3} \), a Lewis base, forming the compound \( \mathrm{F}_{3}\mathrm{B} - \mathrm{NH}_{3} \).

Step 2: Analyze Statement (b)

Statement (b) suggests that \( \mathrm{BF}_{3} \) is a volatile liquid at room temperature. This statement is incorrect because \( \mathrm{BF}_{3} \) is actually a gas at room temperature, not a liquid.

Step 3: Analyze Statement (c)

Statement (c) states that \( \mathrm{BF}_{3} \) combines with ether to form boron trifluoride etherate. This is accurate because \( \mathrm{BF}_{3} \) can react with ether through a Lewis acid-base interaction to form a stable complex \( \mathrm{BF}_{3} \mathrm{-} \text{ether} \).

Step 4: Analyze Statement (d)

Statement (d) asserts that \( \mathrm{BF}_{3} \) acts as a Lewis acid. This is indeed correct as \( \mathrm{BF}_{3} \) has an incomplete octet and can accept an electron pair, characterizing its behavior as a Lewis acid.

Step 5: Conclusion: Identify Incorrect Statement

Since statement (b) is the only incorrect assertion regarding \( \mathrm{BF}_{3} \), it is the wrong statement among the provided options.

Key Concepts

Lewis Acid

Boron Trifluoride (\( \mathrm{BF}_{3} \)) is an excellent example of a Lewis acid. A Lewis acid is defined by its ability to accept an electron pair. \( \mathrm{BF}_{3} \) fits this description perfectly because it has an empty p-orbital that can accept electron pairs.
When \( \mathrm{BF}_{3} \) interacts with a Lewis base, such as ammonia (\( \mathrm{NH}_{3} \)), it readily forms a coordinate covalent bond. This bond occurs when the nitrogen atom from \( \mathrm{NH}_{3} \), which has a lone pair of electrons, donates this pair to the boron atom in \( \mathrm{BF}_{3} \).

• \( \mathrm{BF}_{3} \) has three covalent bonds with fluorine atoms, but the boron atom lacks a full octet of electrons.
• This deficiency makes boron very reactive with substances that can provide electron pairs.
• The resultant complex from \( \mathrm{BF}_{3} \) and \( \mathrm{NH}_{3} \) is called \( \mathrm{F}_{3}\mathrm{B} - \mathrm{NH}_{3} \).

The reactivity of \( \mathrm{BF}_{3} \) as a Lewis acid is crucial in its interactions with other substances and forms the foundation of many complex chemical reactions.

Addition Compound

An addition compound involves the formation of a new compound resulting from the combination of two distinct molecules. In the case of \( \mathrm{BF}_{3} \) and \( \mathrm{NH}_{3} \), the formation of the addition compound \( \mathrm{F}_{3}\mathrm{B} - \mathrm{NH}_{3} \) is an exemplary process.
\( \mathrm{F}_{3}\mathrm{B} - \mathrm{NH}_{3} \) showcases the Lewis acid-base interaction vividly as the electron-deficient boron atom accepts electrons from the lone pair of \( \mathrm{NH}_{3} \). This process stabilizes both molecules into a new complex.

• The new bond between boron and nitrogen involves the sharing of the donated electron pair.
• It's through these interactions that many new and useful compounds are synthesized in the chemical industry.
• The resulting compound has different properties compared to its individual components.

Such addition compounds are widespread in various chemical domains and are essential in understanding molecular interactions.

Volatile Liquid

A volatile liquid is a substance that easily evaporates at room temperature due to its high vapor pressure. However, Boron Trifluoride (\( \mathrm{BF}_{3} \)) is not a volatile liquid. Instead, it exists as a gas at room temperature.
The term 'volatile' can often lead to misconceptions about the state of certain compounds. While \( \mathrm{BF}_{3} \) is indeed volatile, it's crucial to note:

• \( \mathrm{BF}_{3} \) is found as a gas under standard room conditions, not a liquid.
• When discussing chemicals, differentiating between a gas and a volatile liquid is important for understanding their physical behavior.
• Mistaken classification of \( \mathrm{BF}_{3} \) as a liquid can lead to errors in laboratory or industrial applications.

Grasping the correct state of \( \mathrm{BF}_{3} \) is important when handling or studying this chemical in scientific endeavors.