AP-style-questions-unit-8 Page 1

📘 Unit 8 – AP Style MCQs with Feedback (1–5)

1. Which of the following can be made by partially neutralizing an acid?

A) BaClOH
B) KOH
C) NaHCO₃
D) MgCO₃

✅ Correct! In this response, carbonic acid, H₂CO₃, is half-neutralized to produce the bicarbonate ion, HCO₃⁻.

❌ A is incorrect: This response is meaningless and not formed by neutralizing an acid.

❌ B is incorrect: KOH is a base that has not reacted with any acid.

❌ D is incorrect: Possibly Mg(OH)₂ reacted completely with H₂CO₃ – this isn't partial neutralization.

2. A solution containing HF is titrated with KOH. At the end point, the solution contains:

A) Equal amounts of HF and KOH
B) KF and H₂O
C) K⁺ and F⁻
D) All ions: H₂O, H⁺, OH⁻, etc.

✅ Correct! The question asks what the solution contains. Therefore, the best answer is to list everything no matter how small the concentrations. Aqueous solutions always contain water along with H+ and OH−. The major solutes are the ions K+ and F−. A small amount of F− hydrolyzes water to generate HF too.

❌ A is incorrect:

❌ B is incorrect:

❌ C is incorrect: .

3. A buffer at pH 5.32 is prepared from a weak acid with a pKa = 5.15. If 100 mL is diluted to 200 mL, what is the pH?

A) 5.02
B) 5.32
C) 5.62
D) Need acid identity

✅ Correct! pH doesn’t change upon dilution – the ratio of acid/base stays the same.

❌ A is incorrect: pH does not drop when diluted – ratio is unchanged.

❌ C is incorrect: pH doesn’t rise on dilution unless ratio changes.

❌ D is incorrect: You don’t need acid identity – only the ratio matters.

4. Which pair creates a buffer?

A) Cu(OH)₂ and CuCl₂
B) KOH and NaHCO₃
C) LiHCO₃ and K₂CO₃
D) Na₂CO₃ and H₂SO₃

✅ Correct! These give HCO₃⁻ and CO₃²⁻, a conjugate acid–base pair = buffer!

❌ A is incorrect: Not a true conjugate acid–base pair.

❌ B is incorrect: Strong base + weak base salt = not buffer-forming.

❌ D is incorrect: Doesn’t yield conjugate pairs in needed proportions.

5. Which of the following has the highest pH?

A) 0.100 M HCl
B) 0.200 M HC₂H₃O₂
C) 0.100 M Na₂CO₃
D) 0.200 M NaCl

✅ Correct! Carbonic acid is weaker than acetic → stronger base = higher pH.

❌ A is incorrect: HCl is a strong acid, gives very low pH.

❌ B is incorrect: Acetic acid has pH < 7 – not high.

❌ D is incorrect: NaCl doesn’t affect pH – it’s neutral.

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