AP Chemistry: Acids & Bases 3 — Questions and Answers
Question 1: The acid dissociation constant Ka of a weak acid is 1.0 × 10^-5. What is its pKa?
- 5 (Correct answer)
- 9
- -5
- 14
Correct answer: 5
pKa = -log(Ka) = -log(1.0 × 10^-5) = 5.
Question 2: Which of these is the strongest acid based on Ka values?
- Ka = 1.8 × 10^-5
- Ka = 6.3 × 10^-3 (Correct answer)
- Ka = 4.0 × 10^-10
- Ka = 1.0 × 10^-7
Correct answer: Ka = 6.3 × 10^-3
A larger Ka means greater dissociation, so 6.3 × 10^-3 is the strongest acid.
Question 3: What salt is produced when HCl reacts with NaOH?
- NaCl (Correct answer)
- NaClO
- Na2O
- NaH
Correct answer: NaCl
Neutralization of HCl with NaOH produces NaCl and water.
Question 4: An aqueous solution of NH4Cl is expected to be:
- Acidic (Correct answer)
- Basic
- Neutral
- Amphoteric
Correct answer: Acidic
The ammonium ion (NH4+) hydrolyzes to release H+, making the solution acidic.
Question 5: In the Lewis theory, an acid is a substance that:
- Accepts an electron pair (Correct answer)
- Donates an electron pair
- Donates a proton
- Accepts a proton
Correct answer: Accepts an electron pair
A Lewis acid is an electron-pair acceptor.
Question 6: If [H+] in a solution is 2.0 × 10^-3 M, the approximate pH is:
- 2.7 (Correct answer)
- 3.0
- 1.3
- 11.3
Correct answer: 2.7
pH = -log(2.0 × 10^-3) ≈ 2.7.
Question 7: Which indicator would best signal the equivalence point of a strong acid–strong base titration?
- Phenolphthalein
- Methyl orange
- Either works well (Correct answer)
- Litmus only
Correct answer: Either works well
Strong acid–strong base titrations have a sharp pH jump around 7, so either indicator works.
AP Chemistry: Acids & Bases 3
The acid dissociation constant Ka of a weak acid is 1.0 × 10^-5.
What is its pKa?