Questions on Lewis Acids and Bases
20 Multiple-Choice Questions on Lewis Acids and Bases
1. A Lewis acid is defined as a substance that:
A) Donates a proton
B) Accepts a proton
C) Accepts an electron pair
D) Donates a hydroxide ion
E) Produces H⁺ in water
2. A Lewis base is defined as a substance that:
A) Donates a proton
B) Accepts a hydroxide ion
C) Accepts an electron pair
D) Donates an electron pair
E) Produces OH⁻ in water
3. Which of the following is a Lewis base?
A) BF₃
B) AlCl₃
C) NH₃
D) H⁺
E) Fe³⁺
4. Which species can act as a Lewis acid?
A) OH⁻
B) NH₃
C) Cl⁻
D) BF₃
E) CH₄
5. Which of the following best describes a Lewis acid-base reaction?
A) Transfer of H⁺ ions
B) Transfer of OH⁻ ions
C) Exchange of water molecules
D) Formation of a covalent bond through electron pair donation
E) Neutralization involving salt formation
6. In the reaction:
BF₃ + :NH₃ → F₃B←NH₃,
which is the Lewis acid?
A) BF₃
B) NH₃
C) F⁻
D) B
E) H⁺
7. What is the Lewis base in the reaction above?
A) NH₃
B) BF₃
C) F⁻
D) B
E) H₂O
8. Which of the following is not a Lewis acid?
A) Fe³⁺
B) H⁺
C) CO₂
D) OH⁻
E) Al³⁺
9. Which of the following can act as a Lewis base?
A) H⁺
B) BCl₃
C) NH₃
D) AlBr₃
E) Zn²⁺
10. What type of bond is formed in a Lewis acid-base reaction?
A) Ionic bond
B) Covalent bond
C) Metallic bond
D) Hydrogen bond
E) Van der Waals interaction
11. In the reaction:
Ag⁺ + 2NH₃ → [Ag(NH₃)₂]⁺,
what role does NH₃ play?
A) Lewis acid
B) Bronsted acid
C) Lewis base
D) Oxidizing agent
E) Catalyst
12. In the same reaction above, Ag⁺ acts as:
A) Lewis base
B) Lewis acid
C) Reducing agent
D) Spectator ion
E) Catalyst
13. Which of the following molecules has a lone pair and can donate it in a Lewis acid-base reaction?
A) Na⁺
B) H₂
C) NH₃
D) CH₄
E) HCl
14. The Lewis acid in the complex [Fe(CN)₆]³⁻ is:
A) CN⁻
B) Fe³⁺
C) H₂O
D) Fe(CN)₆³⁻
E) OH⁻
15. The central idea of Lewis acid-base theory is:
A) Transfer of protons
B) Sharing of electrons
C) Formation of ionic compounds
D) Exchange of H⁺ and OH⁻
E) Water dissociation
16. Which of the following is a characteristic of Lewis bases?
A) Electron pair acceptors
B) Electron-deficient
C) Typically cations
D) Possess lone electron pairs
E) Always acids in water
17. In the reaction CO₂ + OH⁻ → HCO₃⁻, the Lewis base is:
A) CO₂
B) HCO₃⁻
C) OH⁻
D) H⁺
E) CO
18. In the same reaction, the Lewis acid is:
A) OH⁻
B) CO₂
C) HCO₃⁻
D) H⁺
E) O²⁻
19. Which of the following is most likely to act as a Lewis acid?
A) NH₃
B) CH₄
C) Mg²⁺
D) OH⁻
E) H₂O
20. A Lewis acid must have:
A) A proton to donate
B) A positive charge
C) A pair of electrons to share
D) An empty orbital to accept electrons
E) A hydroxide group
Answer Key with Full Explanations
1. C – Lewis acids accept electron pairs.
2. D – Lewis bases donate electron pairs.
3. C – NH₃ has a lone pair to donate = Lewis base.
4. D – BF₃ has an empty orbital = Lewis acid.
5. D – Lewis acid-base reactions form coordinate covalent bonds via electron pair sharing.
6. A – BF₃ accepts a lone pair from NH₃ = Lewis acid.
7. A – NH₃ donates the lone pair = Lewis base.
8. D – OH⁻ has a lone pair and donates it = base, not acid.
9. C – NH₃ donates electrons = Lewis base.
10. B – The bond formed is covalent (specifically, a coordinate covalent bond).
11. C – NH₃ donates lone pairs to Ag⁺ = Lewis base.
12. B – Ag⁺ accepts electrons from NH₃ = Lewis acid.
13. C – NH₃ has a lone pair and can donate it.
14. B – Fe³⁺ accepts electron pairs from CN⁻ = Lewis acid.
15. B – Central concept: donation and acceptance of electron pairs.
16. D – Lewis bases have lone electron pairs.
17. C – OH⁻ donates an electron pair to CO₂.
18. B – CO₂ accepts the pair = Lewis acid.
19. C – Mg²⁺ is electron-deficient = strong Lewis acid.
20. D – An empty orbital is required to accept electrons = key Lewis acid trait.
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