Buffer capacity MCQs With Answer

Buffer capacity MCQs With Answer

by

Buffer capacity MCQs With Answer for B. Pharm students provides a focused review of buffer theory, calculations, and pharmaceutical applications. This introduction covers key concepts such as Henderson-Hasselbalch equation, pKa, buffer range, buffer index, and effects of dilution, ionic strength, and temperature on buffering ability. These MCQs emphasize real-world formulation issues—choosing suitable buffers for drug stability, biological compatibility, and titration interpretation—helping pharmacy students sharpen quantitative skills and conceptual understanding. The set is ideal for exam prep, practical labs, and formulation design revision. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the definition of buffer capacity?

  • The concentration of buffer components only
  • The amount of strong acid or base required to change the pH by one unit per liter
  • The pKa of the buffer system
  • The pH at half-neutralization

Correct Answer: The amount of strong acid or base required to change the pH by one unit per liter

Q2. Which equation is most commonly used to calculate the pH of a buffer solution?

  • van’t Hoff equation
  • Henderson-Hasselbalch equation
  • Arrhenius equation
  • Debye-Hückel equation

Correct Answer: Henderson-Hasselbalch equation

Q3. For a buffer composed of acetic acid (pKa 4.76) and acetate, at what pH is the buffer capacity maximum?

  • pH 3.76
  • pH 4.76
  • pH 5.76
  • Depends on total concentration

Correct Answer: pH 4.76

Q4. The useful buffering range of a weak acid is typically:

  • pKa ± 0.1
  • pKa ± 1
  • pKa ± 3
  • pKa ± 5

Correct Answer: pKa ± 1

Q5. Which of the following increases buffer capacity most effectively?

  • Decreasing both acid and conjugate base concentrations
  • Increasing ionic strength only
  • Increasing total concentration of buffering species
  • Raising the temperature substantially

Correct Answer: Increasing total concentration of buffering species

Q6. In Henderson-Hasselbalch form, pH = pKa + log([A-]/[HA]). If [A-] = [HA], the pH equals:

  • pKa – 1
  • pKa
  • pKa + 1
  • 0

Correct Answer: pKa

Q7. Which buffer system is commonly used in pharmaceutical formulations for pH around 7.4?

  • Acetate buffer
  • Phosphate buffer
  • Formate buffer
  • Citrate buffer at pH 2

Correct Answer: Phosphate buffer

Q8. For a buffer with pKa 6.0, which pH is least suitable for strong buffering?

  • pH 5.0
  • pH 6.0
  • pH 7.0
  • pH 9.0

Correct Answer: pH 9.0

Q9. What is the effect of adding a small amount of strong acid to a buffer?

  • It converts conjugate base to acid, resisting pH change
  • It converts acid to conjugate base, increasing pH
  • No reaction occurs, pH changes drastically
  • Buffer capacity is instantly lost

Correct Answer: It converts conjugate base to acid, resisting pH change

Q10. Which term describes the buffer’s resistance to pH change upon addition of acid or base?

  • Buffer index
  • Buffer range
  • Buffer concentration
  • Buffer molarity

Correct Answer: Buffer index

Q11. The half-equivalence point in a titration of a weak acid with strong base corresponds to:

  • pH = 7
  • pH = pKa
  • pH = pKb
  • pH = pKa + 1

Correct Answer: pH = pKa

Q12. Which buffer is most appropriate for stabilizing proteins near physiological pH with minimal metal chelation?

  • Citrate buffer
  • Phosphate buffer
  • Acetate buffer
  • Tris buffer

Correct Answer: Phosphate buffer

Q13. The buffer capacity is highest when the ratio [A-]/[HA] is approximately:

  • 0.01
  • 0.1
  • 1
  • 100

Correct Answer: 1

Q14. How does dilution of a buffer affect its buffer capacity?

  • Capacity increases upon dilution
  • Capacity remains unchanged
  • Capacity decreases upon dilution
  • Capacity becomes infinite

Correct Answer: Capacity decreases upon dilution

Q15. For a buffer containing 0.1 M HA and 0.1 M A-, adding 0.01 mol of strong acid per liter will:

  • Decrease pH slightly due to neutralization of A- to HA
  • Increase pH slightly due to conversion of HA to A-
  • Not change pH at all
  • Completely neutralize the buffer

Correct Answer: Decrease pH slightly due to neutralization of A- to HA

Q16. Which factor does NOT significantly affect buffer capacity?

  • Total concentration of buffer components
  • Ratio of acid to base
  • Temperature
  • Color of the solution

Correct Answer: Color of the solution

Q17. In pharmaceutical formulations, why is buffer selection critical?

  • Buffers determine drug solubility and stability
  • Buffers always make drugs opaque
  • Buffers are irrelevant for drug absorption
  • Buffers only affect manufacturing speed

Correct Answer: Buffers determine drug solubility and stability

Q18. The Henderson-Hasselbalch equation assumes which of the following approximations?

  • Activities equal concentrations without correction
  • All species are fully ionized
  • Temperature is below 0°C
  • pH equals pKa always

Correct Answer: Activities equal concentrations without correction

Q19. Which buffer system is suitable for controlling pH around 3.5 in formulations?

  • Phosphate buffer
  • Citrate buffer
  • Tris buffer
  • Bicarbonate buffer

Correct Answer: Citrate buffer

Q20. What is the main reason ionic strength affects buffer pH calculations?

  • Ionic strength changes activity coefficients of ions
  • Ionic strength alters pKa numerically but not activities
  • Ionic strength evaporates ions
  • Ionic strength only affects solids, not solutions

Correct Answer: Ionic strength changes activity coefficients of ions

Q21. For a weak base buffer system, which Henderson–Hasselbalch form is used to calculate pH?

  • pH = pKa + log([B]/[BH+])
  • pOH = pKb + log([BH+]/[B]) and pH = 14 – pOH
  • pH = pKb + log([BH+]/[B])
  • pH = pKa – log([B]/[BH+])

Correct Answer: pOH = pKb + log([BH+]/[B]) and pH = 14 – pOH

Q22. Which value best describes buffer range for an acid with pKa = 5.2?

  • pH 3.2–4.2
  • pH 4.2–6.2
  • pH 5.0–5.4
  • pH 6.2–8.2

Correct Answer: pH 4.2–6.2

Q23. When preparing a buffer for parenteral formulation, which criterion is most important?

  • Buffer pH must match vehicle color
  • Buffer must be non-toxic and isotonic
  • Buffer concentration must be maximal for color stability
  • Use the buffer with the highest molecular weight

Correct Answer: Buffer must be non-toxic and isotonic

Q24. The buffer capacity (β) is mathematically defined as:

  • d[H+]/dpH
  • dC/dpH where C is total concentration
  • The amount of acid/base added per unit pH change per unit volume
  • pKa × pH

Correct Answer: The amount of acid/base added per unit pH change per unit volume

Q25. Which of the following is TRUE about buffer capacity near equivalence point in titration?

  • Buffer capacity is highest at equivalence point
  • Buffer capacity is minimal at equivalence point for weak acid-strong base titration
  • Equivalence point equals half-neutralization point
  • Buffer capacity is independent of concentration at equivalence

Correct Answer: Buffer capacity is minimal at equivalence point for weak acid-strong base titration

Q26. In a mixture of a weak acid (HA) and its salt (A-), which species primarily consumes added strong base?

  • HA
  • A-
  • Water
  • Buffer does not react with base

Correct Answer: HA

Q27. For a buffer made from acetic acid (pKa 4.76) with [HA]=0.05 M and [A-]=0.15 M, the pH is:

  • 3.76
  • 4.17
  • 4.76
  • 5.36

Correct Answer: 5.36

Q28. The common ion effect in buffers causes:

  • Increased degree of ionization of the weak acid
  • Suppression of ionization of the weak acid
  • No change in ionization
  • Complete precipitation of buffer components

Correct Answer: Suppression of ionization of the weak acid

Q29. What happens to buffer pH when temperature changes significantly for systems with temperature-dependent pKa?

  • pH remains constant regardless of temperature
  • pH may shift due to change in pKa with temperature
  • Buffer components precipitate always
  • Buffer capacity increases linearly with temperature

Correct Answer: pH may shift due to change in pKa with temperature

Q30. Which buffer is typically avoided in formulations containing divalent metal ions due to chelation?

  • Phosphate buffer
  • Citrate buffer
  • Acetate buffer
  • Borate buffer

Correct Answer: Citrate buffer

Q31. When pH = pKa, the ratio [A-]/[HA] equals:

  • 0
  • 0.1
  • 1
  • 10

Correct Answer: 1

Q32. Which statement about buffer capacity and pH distance from pKa is correct?

  • Buffer capacity increases as pH moves far from pKa
  • Buffer capacity is maximal at pH = pKa and falls as pH deviates
  • Buffer capacity is unaffected by pH relative to pKa
  • Buffer capacity is zero at pH = pKa

Correct Answer: Buffer capacity is maximal at pH = pKa and falls as pH deviates

Q33. For a buffer of 0.2 M total concentration, doubling both HA and A- concentrations will:

  • Maintain same pH but increase buffer capacity
  • Change pH to the pKa
  • Reduce buffer capacity
  • Eliminate buffering action

Correct Answer: Maintain same pH but increase buffer capacity

Q34. In practice, which buffer is commonly used for biochemical assays at pH ~8.0?

  • Acetate
  • Tris
  • Citrate
  • Formate

Correct Answer: Tris

Q35. The Henderson-Hasselbalch equation can fail in accuracy primarily because:

  • It ignores activity coefficients at higher ionic strength
  • It assumes perfect solubility of salts
  • It requires temperatures below freezing
  • It treats water as an acid

Correct Answer: It ignores activity coefficients at higher ionic strength

Q36. Which is the best buffer choice for maintaining pH in an ophthalmic solution where eye irritation must be minimized?

  • Strong acid buffer
  • Physiologically compatible buffer at near-neutral pH
  • Very concentrated acetate buffer at pH 2
  • Highly alkaline buffer

Correct Answer: Physiologically compatible buffer at near-neutral pH

Q37. Which describes buffer index (β) in relation to buffer concentration and pKa?

  • β is independent of concentration and pKa
  • β increases with total concentration and is highest near pKa
  • β only depends on pH meters used
  • β is maximal when pH is 14

Correct Answer: β increases with total concentration and is highest near pKa

Q38. For a diprotic acid with two pKa values, an effective buffer region exists around:

  • Only the first pKa
  • Only the second pKa
  • Each pKa ±1, giving two buffer regions
  • No buffer region exists for diprotic acids

Correct Answer: Each pKa ±1, giving two buffer regions

Q39. If a buffer solution shows decreasing pH after storage, which is a likely cause?

  • CO2 absorption from air forming carbonic acid
  • Loss of water by evaporation only
  • Buffer components spontaneously generate base
  • Temperature decreased to absolute zero

Correct Answer: CO2 absorption from air forming carbonic acid

Q40. Which analytical practice improves accuracy of buffer pH calculations in concentrated ionic solutions?

  • Ignoring activity coefficients
  • Using activity coefficients or ionic strength corrections
  • Assuming pH meter is calibrated for pure water only
  • Adding strong acid to all buffers

Correct Answer: Using activity coefficients or ionic strength corrections

Q41. Which buffer component pairing is commonly used for pH 4–6 in pharmaceutical formulations?

  • Ammonia/ammonium
  • Acetic acid/acetate
  • Tris/HCl
  • Borate/boric acid

Correct Answer: Acetic acid/acetate

Q42. A buffer prepared with 0.05 M HA and 0.15 M A- will have a pH that is:

  • Lower than pKa
  • Equal to pKa
  • Higher than pKa
  • Undefined

Correct Answer: Higher than pKa

Q43. Which statement about bicarbonate buffer in physiological systems is correct?

  • Bicarbonate buffer is not important in blood pH regulation
  • Bicarbonate buffer works with respiratory CO2 control to regulate pH
  • Bicarbonate buffer is the only buffer with fixed pKa independent of CO2
  • Bicarbonate buffer is ideal for long-term pharmaceutical storage

Correct Answer: Bicarbonate buffer works with respiratory CO2 control to regulate pH

Q44. For making a buffer at specific pH using Henderson-Hasselbalch, you must know:

  • Only the pH meter brand
  • pKa of the buffering acid and desired ratio of conjugate base to acid
  • The boiling point of water
  • The solubility constant of sodium chloride

Correct Answer: pKa of the buffering acid and desired ratio of conjugate base to acid

Q45. The buffer capacity toward addition of acid is greatest when:

  • [A-] >> [HA]
  • [HA] >> [A-]
  • [HA] ≈ [A-]
  • Only water is present

Correct Answer: [HA] ≈ [A-]

Q46. During titration of a weak base with strong acid, the pH at half-neutralization equals:

  • pKa of its conjugate acid
  • pKb of base directly
  • 14 – pKb
  • pH = 7 always

Correct Answer: pKa of its conjugate acid

Q47. Which buffer is commonly used for gel formulations requiring pH ~5.5 and minimal irritation?

  • Strong alkaline buffer
  • Citrate-acetate mixed buffer
  • Concentrated hydrochloric acid
  • Pure water

Correct Answer: Citrate-acetate mixed buffer

Q48. What is the effect of adding a salt of the conjugate base to a weak acid solution?

  • It lowers the pH by increasing HA concentration
  • It increases pH by adding A- and reduces ionization of HA
  • It causes precipitation of HA always
  • It has no chemical effect

Correct Answer: It increases pH by adding A- and reduces ionization of HA

Q49. Which practical step helps maintain buffer pH during storage of sensitive pharmaceuticals?

  • Use open containers exposed to air
  • Package under inert atmosphere and control CO2 exposure
  • Store at very high temperatures to accelerate reactions
  • Add excess strong acid unsafely

Correct Answer: Package under inert atmosphere and control CO2 exposure

Q50. The buffering action near pKa is primarily due to:

  • High solubility of the buffer salt only
  • Rapid interconversion between acid and conjugate base minimizing pH change
  • Formation of precipitates that absorb H+ or OH-
  • Reaction with atmospheric nitrogen

Correct Answer: Rapid interconversion between acid and conjugate base minimizing pH change

Leave a Comment