Classification of acid–base titrations MCQs With Answer

Classification of acid–base titrations MCQs With Answer

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Classification of acid–base titrations MCQs With Answer provides B.Pharm students a focused review of titration types, titration curves, and indicator selection. This concise guide covers strong acid–strong base, strong acid–weak base, weak acid–strong base, and weak acid–weak base titrations, plus polyprotic systems, buffer regions, half‑equivalence concepts, and salt hydrolysis effects. Emphasis is on equivalence point pH, choice of appropriate indicators, pKa relationships, and interpreting titration curves for drug analysis and pharmaceutical quality control. Each MCQ tests conceptual understanding, calculations, and practical applications relevant to pharmacology and formulation. Use these practice questions to sharpen analytical skills and exam readiness. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which titration classification typically gives an equivalence point pH very close to 7?

  • Titration of a strong acid with a strong base
  • Titration of a weak acid with a strong base
  • Titration of a strong acid with a weak base
  • Titration of a weak acid with a weak base

Correct Answer: Titration of a strong acid with a strong base

Q2. For titration of a weak acid with a strong base, the pH at equivalence is generally:

  • Less than 7
  • Equal to 7
  • Greater than 7
  • Unpredictable without initial concentration

Correct Answer: Greater than 7

Q3. At the half‑equivalence point of a weak acid titrated with a strong base, the pH equals:

  • pKa of the acid
  • pKb of the conjugate base
  • 7.00
  • twice the pKa

Correct Answer: pKa of the acid

Q4. Which indicator is most appropriate for titrating acetic acid (pKa 4.76) with NaOH?

  • Phenolphthalein (color change ~8.2–10.0)
  • Methyl orange (color change ~3.1–4.4)
  • Bromocresol green (color change ~3.8–5.4)
  • Thymol blue (first range ~1.2–2.8)

Correct Answer: Phenolphthalein (color change ~8.2–10.0)

Q5. During titration of a weak base with a strong acid, the equivalence point pH is generally:

  • Less than 7 due to formation of a weak acid from the conjugate acid
  • Equal to 7 because strong acid neutralizes base
  • Greater than 7 because salts produce OH-
  • Always exactly 7.00 at 25°C

Correct Answer: Less than 7 due to formation of a weak acid from the conjugate acid

Q6. Which phenomenon causes the equivalence point pH of a weak acid titration to be basic?

  • Hydrolysis of the conjugate base produced by neutralization
  • Autodissociation of water being high
  • Presence of strong acid excess
  • Indicator adsorption on electrode

Correct Answer: Hydrolysis of the conjugate base produced by neutralization

Q7. In a diprotic acid titration (H2A) with a strong base, the number of equivalence points observed in the titration curve is:

  • Two equivalence points for stepwise deprotonation
  • One equivalence point only
  • Three equivalence points including a buffer plateau
  • None, because pH changes continuously

Correct Answer: Two equivalence points for stepwise deprotonation

Q8. The buffer region in a titration curve corresponds to which region?

  • Where appreciable amounts of both acid and its conjugate base are present
  • Only at the equivalence point
  • After complete neutralization only
  • When only pure solvent is present

Correct Answer: Where appreciable amounts of both acid and its conjugate base are present

Q9. Which titration type is most difficult to detect an endpoint visually due to a very gradual pH change?

  • Weak acid titrated with weak base
  • Strong acid titrated with strong base
  • Weak acid titrated with strong base
  • Strong acid titrated with weak base

Correct Answer: Weak acid titrated with weak base

Q10. The pH at equivalence for titration of benzoic acid (Ka = 6.3×10^-5) with NaOH can be estimated by calculating:

  • Hydrolysis of benzoate ion using Kb = Kw/Ka
  • Directly using Ka without further steps
  • Assuming pH = 7 because NaOH is strong
  • Using pKa + pKb = 14

Correct Answer: Hydrolysis of benzoate ion using Kb = Kw/Ka

Q11. Which statement best distinguishes equivalence point from endpoint in titration?

  • Equivalence point is theoretical stoichiometric completion; endpoint is observed signal such as color change
  • Equivalence point is color change; endpoint is stoichiometric point
  • Both terms are interchangeable and mean the same
  • Endpoint occurs before titration begins

Correct Answer: Equivalence point is theoretical stoichiometric completion; endpoint is observed signal such as color change

Q12. For a monoprotic weak acid titrated with a strong base, the steepest pH jump occurs near:

  • The equivalence point
  • The initial titration point only
  • Halfway through the buffer region
  • After adding large excess of base

Correct Answer: The equivalence point

Q13. A student titrates 25.0 mL of 0.10 M HA (weak acid) with 0.10 M NaOH. At half‑equivalence volume, the concentration of A- equals:

  • The initial concentration of HA divided by 2
  • Zero
  • Twice the initial concentration of HA
  • The concentration of OH- added

Correct Answer: The initial concentration of HA divided by 2

Q14. Which plot technique is commonly used to locate equivalence point precisely from a titration curve?

  • First derivative (dpH/dV) or second derivative method
  • Plotting pH vs time only
  • Using conductivity plots exclusively
  • Counting endpoint color changes by eye

Correct Answer: First derivative (dpH/dV) or second derivative method

Q15. When selecting an indicator, the indicator’s pKa should approximate which feature of the titration?

  • The pH at the equivalence point
  • The initial solution pH only
  • The pH of pure water (7.00)
  • Twice the pKa of the analyte

Correct Answer: The pH at the equivalence point

Q16. In titration of a polyprotic acid, buffer regions appear:

  • Between successive equivalence points where pH ≈ pKa
  • Only after the last equivalence point
  • Only at the initial concentration
  • Never, because polyprotic acids do not form buffers

Correct Answer: Between successive equivalence points where pH ≈ pKa

Q17. Which effect will increasing the initial concentration of a weak acid have on its titration curve (same titrant concentration)?

  • The pH jump at equivalence becomes steeper (sharper endpoint)
  • The equivalence pH shifts to acidic values automatically
  • The half‑equivalence point disappears
  • No change at all in the titration curve shape

Correct Answer: The pH jump at equivalence becomes steeper (sharper endpoint)

Q18. During titration of a weak acid with strong base, the buffer capacity is maximum when:

  • pH = 7.00 always
  • Concentrations of acid and base are both zero
  • Only at the equivalence point

Correct Answer: =pH = pKa of the acid

Q19. Which salt formed at equivalence is most likely to hydrolyze to produce an acidic solution?

  • NH4Cl (from NH3 and HCl)
  • NaCl (from NaOH and HCl)
  • NaCH3COO (from CH3COOH and NaOH)
  • K2SO4 (from strong acid and strong base)

Correct Answer: NH4Cl (from NH3 and HCl)

Q20. In a titration where the titrant and analyte are both weak (weak acid vs weak base), visual indicators are unreliable because:

  • The pH change at equivalence is very small and gradual
  • Indicators react chemically with titrant
  • There is no equivalence point in such titrations
  • The titration mixture becomes colorless only

Correct Answer: The pH change at equivalence is very small and gradual

Q21. For titration of a 0.10 M monoprotic weak acid (Ka small) with 0.10 M NaOH, the pH at the equivalence depends primarily on:

  • The Ka of the weak acid through hydrolysis of the conjugate base
  • The initial color of the solution
  • The standard hydrogen electrode potential only
  • The molar mass of the acid exclusively

Correct Answer: The Ka of the weak acid through hydrolysis of the conjugate base

Q22. Why is phenolphthalein often chosen for titrating weak acids with strong bases?

  • Because its transition range lies within the steep basic region around equivalence
  • Because it is red in acidic medium
  • Because it reacts with acetic acid to form a precipitate
  • Because it has a transition range below pH 4

Correct Answer: Because its transition range lies within the steep basic region around equivalence

Q23. In titration of a 25.0 mL sample of 0.10 M HCl with 0.10 M NaOH, the volume of NaOH required at equivalence is:

  • 25.0 mL
  • 12.5 mL
  • 50.0 mL
  • 10.0 mL

Correct Answer: 25.0 mL

Q24. Which statement about titration of a weak diprotic acid H2A is correct?

  • If pKa1 and pKa2 differ by >3 units, two distinct equivalence points are easily observed
  • Two equivalence points are always merged regardless of pKa separation
  • Diprotic acids never form buffer regions
  • Equivalence pH is always equal to 7 for diprotic acids

Correct Answer: If pKa1 and pKa2 differ by >3 units, two distinct equivalence points are easily observed

Q25. In an acid–base titration, the titrant is defined as:

  • The solution of known concentration added to the analyte
  • The unknown analyte being titrated
  • The indicator used to show the endpoint
  • The burette itself irrespective of solution

Correct Answer: The solution of known concentration added to the analyte

Q26. Which calculation is used to find pH at the half‑neutralization point for a weak monoprotic acid?

  • pH = pKa (Henderson–Hasselbalch where [HA] = [A-])
  • pH = 14 − pKa
  • pH = 7 regardless of pKa
  • pH = log(Ka) only

Correct Answer: pH = pKa (Henderson–Hasselbalch where [HA] = [A-])

Q27. During titration, a wide flat plateau in the pH curve indicates:

  • A buffer region where pH changes slowly with addition of titrant
  • Immediate precipitation of the analyte
  • Complete absence of acid or base
  • Instrumental error only

Correct Answer: A buffer region where pH changes slowly with addition of titrant

Q28. Which method improves precision when endpoints are difficult to judge visually in acid–base titrations?

  • Use of a potentiometric (pH meter) titration to detect equivalence
  • Adding indicator at the very start and never observing color change
  • Performing titration in total darkness
  • Mixing titrant and analyte without stirring

Correct Answer: Use of a potentiometric (pH meter) titration to detect equivalence

Q29. For titration involving amphoteric substances (e.g., amino acids), the titration curve may show:

  • Multiple buffer regions and one or more isoelectric points
  • Only a single abrupt jump at pH 7
  • No buffering behavior at any pH
  • Only endpoints dictated by redox chemistry

Correct Answer: Multiple buffer regions and one or more isoelectric points

Q30. Which factor most influences the choice of indicator for an acid–base titration in pharmaceutical analysis?

  • The pH range of the indicator relative to the titration equivalence pH
  • The solubility of the indicator in organic solvents only
  • The boiling point of the solvent
  • The melting point of the analyte

Correct Answer: The pH range of the indicator relative to the titration equivalence pH

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