18.1 Lewis Acids and Bases

Which of the following is a characteristic property of Lewis acids?

A. They donate electron pairs.

B. They accept electron pairs.

C. They have a full valence shell.

D. They are always gaseous in nature.

Which element is commonly used as a catalyst due to its ability to act as a Lewis acid?

A. Oxygen

B. Hydrogen

C. Boron

D. Nitrogen

What distinguishes transition metals from main group elements?

A. They have a complete d subshell.

B. They are found in the f-block of the periodic table.

C. They form coloured compounds.

D. They have a high electronegativity.

Which block of the periodic table contains elements that are filling their f orbitals?

A. s-block

B. p-block

C. d-block

D. f-block

Which of the following elements is NOT a Lewis base?

A. NH₃

B. H₂O

C. BF₃

D. OH⁻

a) Define a Lewis acid and a Lewis base, providing an example for each. [2]

b) How do Lewis acids and bases differ from the Brønsted-Lowry theory of acids and bases? [3]

a) Why are Lewis acids often referred to as electron-pair acceptors? [2]

b) Given the reaction: BF3 + NH3 -> BF3NH3, identify the Lewis acid and the Lewis base. [2]

Answer:

a) What is the significance of Lewis acids in catalysis? [3]

b) Provide an example of a reaction where a Lewis acid acts as a catalyst. [2]

a) Describe the role of Lewis acids in the formation of coloured compounds. [3]

b) Why are transition metals often associated with Lewis acid behaviour? [2]

c) Provide an example of a coloured compound formed due to the action of a Lewis acid. [2]

a) How does the concept of Lewis acids and bases help in understanding reactions beyond aqueous solutions? [3]

b) Explain the term "hard and soft acids and bases" in the context of Lewis theory. [3]

c) Why is BF3 a Lewis acid even though it doesn't have a hydrogen ion to donate? [2]