Buffer equation MCQs With Answer

Mastering the Buffer equation MCQs With Answer is essential for B. Pharm students preparing for exams and practical formulation work. This concise, SEO-focused introduction covers the Henderson-Hasselbalch equation, pKa relationships, pH calculation, buffer capacity, buffer range, and practical tips for pharmaceutical buffer preparation. Emphasis is placed on real-world pharmaceutical examples—acetate, phosphate, bicarbonate and Good buffers—plus effects of dilution, ionic strength, temperature, and strong acid/base addition. These targeted MCQs help reinforce calculation skills and conceptual understanding needed in pharmaceutics, biopharmaceutics, and quality control. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What does the Henderson-Hasselbalch equation primarily relate?

• The hydrogen ion concentration directly to ionic strength
• The pH of a buffer solution to the pKa and ratio of conjugate base/acid
• The boiling point of a solution to solute concentration
• The osmotic pressure to molecular weight

Correct Answer: The pH of a buffer solution to the pKa and ratio of conjugate base/acid

Q2. Using Henderson-Hasselbalch, if pKa = 4.76 and [A-]/[HA] = 1, what is the pH?

• 3.76
• 4.76
• 5.76
• 6.76

Correct Answer: 4.76

Q3. If you need a buffer at pH 5.76 and pKa = 4.76, what should the ratio [A-]/[HA] be approximately?

• 0.1
• 1.0
• 10.0
• 100.0

Correct Answer: 10.0

Q4. Which buffer component is commonly used in pharmaceutical formulations for pH around 4.7?

• Bicarbonate buffer
• Acetate buffer
• Tris buffer
• Glycine buffer

Correct Answer: Acetate buffer

Q5. Buffer capacity is highest when:

• The pH is far from the pKa
• Concentrations of acid and base are very low
• Concentrations of acid and base are high and pH ≈ pKa
• No conjugate base is present

Correct Answer: Concentrations of acid and base are high and pH ≈ pKa

Q6. Which statement about buffer range is correct?

• Buffer range extends about ±1 pH unit around the pKa
• Buffer range extends about ±5 pH units around the pKa
• Buffer works only at pH equal to pKa
• Buffer range is independent of pKa

Correct Answer: Buffer range extends about ±1 pH unit around the pKa

Q7. In Henderson-Hasselbalch form for a weak acid HA, which expression is correct?

• pH = pKa + log [HA]/[A-]
• pH = pKa + log [A-]/[HA]
• pH = pKa – log [A-]/[HA]
• pH = pKa * log [A-]/[HA]

Correct Answer: pH = pKa + log [A-]/[HA]

Q8. If adding a small amount of strong acid to a buffer, what happens to pH?

• Large pH drop if buffer capacity is low
• Large pH increase
• No change regardless of buffer composition
• Immediate neutralization with no pH effect

Correct Answer: Large pH drop if buffer capacity is low

Q9. Which buffer is preferred for physiological pH (~7.4) in pharmaceutical formulations?

• Acetate buffer
• Phosphate buffer
• Borate buffer
• Formate buffer

Correct Answer: Phosphate buffer

Q10. Why is ionic strength important when using Henderson-Hasselbalch equation?

• Ionic strength has no influence on pH calculations
• Ionic strength changes activity coefficients, affecting apparent pH
• Ionic strength changes only the color of solutions
• Ionic strength increases pKa values by fixed 1 unit

Correct Answer: Ionic strength changes activity coefficients, affecting apparent pH

Q11. A buffer contains 0.1 M HA and 0.1 M A-. If 0.01 mol of strong base is added to 1 L, what is the primary effect?

• Buffer will be completely destroyed
• HA will convert partially to A-, pH increases slightly
• Buffer pH decreases significantly
• No chemical changes occur

Correct Answer: HA will convert partially to A-, pH increases slightly

Q12. For a diprotic acid with pKa1 and pKa2, which region corresponds to best buffer for second dissociation?

• pH around pKa1
• pH around pKa2
• pH lower than both pKa
• Neutral pH always

Correct Answer: pH around pKa2

Q13. Which of the following is a Good buffer commonly used in biochemical preparations?

• Hydrochloric acid
• Tris (tris(hydroxymethyl)aminomethane)
• Sodium chloride
• Acetic acid at extreme dilution

Correct Answer: Tris (tris(hydroxymethyl)aminomethane)

Q14. When preparing a buffer, why might one choose the conjugate salt rather than titrating the acid?

• Salt ensures no ionic interactions
• Salt addition allows precise control of the [A-]/[HA] ratio
• Titration is faster and always preferred
• Salt increases color stability only

Correct Answer: Salt addition allows precise control of the [A-]/[HA] ratio

Q15. In practice, Henderson-Hasselbalch can be inaccurate at very low concentrations due to:

• Neglecting activity coefficients and ionic strength
• Overestimation of pKa by 10 units
• Temperature independence
• Excess water autoionization being ignored

Correct Answer: Neglecting activity coefficients and ionic strength

Q16. The pKa of acetic acid is 4.76. Which pH would give about equal concentrations of acetic acid and acetate?

• 3.76
• 4.76
• 5.76
• 6.76

Correct Answer: 4.76

Q17. Which is the correct interpretation of buffer capacity (β)?

• β = amount of strong acid or base added to change pH by one unit per liter
• β = pKa multiplied by concentration
• β = inverse of ionic strength
• β = total volume of buffer solution

Correct Answer: β = amount of strong acid or base added to change pH by one unit per liter

Q18. If a buffer system has a high total concentration of acid and base, what happens to its buffer capacity?

• Buffer capacity decreases
• Buffer capacity increases
• Buffer capacity becomes zero
• Buffer capacity depends only on pKa, not concentration

Correct Answer: Buffer capacity increases

Q19. For a solution with pKa 6.0, which pH gives the greatest buffering effect?

• pH 5.0
• pH 6.0
• pH 8.0
• pH 3.0

Correct Answer: pH 6.0

Q20. Which factor can shift the effective pKa of a buffer in a formulation?

• Temperature changes
• Presence of nonionic surfactants only
• Container color
• Time of day

Correct Answer: Temperature changes

Q21. When preparing a phosphate buffer, which species pair is commonly used near pH 7.2?

• H2PO4- / PO4^3-
• H2PO4- / HPO4^2-
• H3PO4 / H2PO4-
• PO4^3- / OH-

Correct Answer: H2PO4- / HPO4^2-

Q22. Which buffer is unsuitable for use with strong oxidizing agents due to reactivity?

• Phosphate buffer
• Tris buffer
• Borate buffer
• Citrate buffer

Correct Answer: Tris buffer

Q23. What is the effect of dilution on buffer pH, assuming ideal behavior?

• pH changes significantly with any dilution
• pH remains approximately constant though capacity decreases
• pH always increases by 1 unit per tenfold dilution
• pH becomes exactly neutral

Correct Answer: pH remains approximately constant though capacity decreases

Q24. Which equation should you use for approximate pH when both acid and base concentrations are comparable?

• Henderson-Hasselbalch equation
• Raoult’s law
• Van’t Hoff equation
• Arrhenius equation

Correct Answer: Henderson-Hasselbalch equation

Q25. Which buffer is commonly used for formulations that require pH around 8–9?

• Acetate buffer
• Tris buffer
• Phosphate buffer
• Formate buffer

Correct Answer: Tris buffer

Q26. When calculating pH using Henderson-Hasselbalch, what approximation is often made for weak acids?

• Concentration equals activity at high ionic strength
• Activities are approximated by concentrations (neglecting activity coefficients)
• Water autoionization is the dominating term
• Temperature effects are always included

Correct Answer: Activities are approximated by concentrations (neglecting activity coefficients)

Q27. Which buffer system is often used for ophthalmic preparations due to compatibility with eye pH?

• Boric acid/borate buffer
• Hydrochloric acid buffer
• Strong base buffer
• Formaldehyde buffer

Correct Answer: Boric acid/borate buffer

Q28. Which practical consideration is critical when choosing a buffer for a drug solution?

• Buffer color only
• Buffer pKa relative to desired pH and drug stability
• Buffer’s ability to fluoresce under UV
• Buffer must always be acidic

Correct Answer: Buffer pKa relative to desired pH and drug stability

Q29. What happens to the ratio [A-]/[HA] if you add a strong base to a buffer?

• Ratio decreases
• Ratio increases
• Ratio remains zero
• Ratio becomes negative

Correct Answer: Ratio increases

Q30. For weak base buffer B and BH+, what Henderson-Hasselbalch-like form applies?

• pH = pKb + log [BH+]/[B]
• pOH = pKb + log [B]/[BH+]
• pH = pKa + log [BH+]/[B]
• pOH = pKa + log [B]/[BH+]

Correct Answer: pOH = pKb + log [B]/[BH+]

Q31. Why might a formulator prefer phosphate buffer over acetate at neutral pH?

• Phosphate has multiple pKa values that cover physiological pH
• Acetate is solid at room temperature
• Phosphate is always less reactive with APIs
• Acetate cannot be sterilized

Correct Answer: Phosphate has multiple pKa values that cover physiological pH

Q32. If pH = pKa + 1, what is [A-]/[HA] approximate ratio?

• 0.1
• 1
• 10
• 100

Correct Answer: 10

Q33. Which of these reduces buffer capacity most significantly?

• Increasing total buffer concentration
• Operating far from the buffer pKa
• Keeping pH near pKa
• Using equimolar acid and base

Correct Answer: Operating far from the buffer pKa

Q34. When titrating a weak acid with strong base, the buffering region is around:

• Initial pH only
• Equivalence point only
• pKa value of the weak acid (before equivalence)
• pH 14 only

Correct Answer: pKa value of the weak acid (before equivalence)

Q35. Which is a limitation of Henderson-Hasselbalch in concentrated solutions?

• It predicts ionic strength accurately
• It neglects non-ideal behavior and activity corrections
• It includes temperature dependence inherently
• It can account for complex formation

Correct Answer: It neglects non-ideal behavior and activity corrections

Q36. A buffer with pKa 3.75 is best used for stabilizing drugs at which approximate pH?

• pH 8.0
• pH 3.8
• pH 6.5
• pH 1.0

Correct Answer: pH 3.8

Q37. Which practical step improves buffer stability against microbial growth?

• Avoiding preservatives entirely
• Using appropriate preservatives and sterile technique
• Keeping pH random
• Adding sugar only

Correct Answer: Using appropriate preservatives and sterile technique

Q38. In pharmaceutical QC, why is pH measurement of buffers done at controlled temperature?

• pH meters only work at one temperature
• Buffer pH depends on temperature, affecting pKa and ionization
• Temperature changes color of buffer
• Temperature does not affect pH

Correct Answer: Buffer pH depends on temperature, affecting pKa and ionization

Q39. For bicarbonate buffer in blood, which gas influences pH via equilibrium?

• Nitrogen gas
• Carbon dioxide (CO2)
• Helium
• Argon

Correct Answer: Carbon dioxide (CO2)

Q40. When choosing a buffer salt, why consider counter-ion compatibility?

• Counter-ions have no effect
• Some counter-ions form insoluble salts or interact with API
• Counter-ions always improve solubility
• Counter-ions determine color only

Correct Answer: Some counter-ions form insoluble salts or interact with API

Q41. Which method is commonly used to prepare a buffer at a desired pH?

• Mixing acid and base forms in proper ratio using Henderson-Hasselbalch
• Adding only strong acid until pH is reached
• Allowing the solution to equilibrate with air
• Heating to change pH

Correct Answer: Mixing acid and base forms in proper ratio using Henderson-Hasselbalch

Q42. What happens to buffer capacity if pH is exactly equal to pKa?

• Buffer capacity is minimal
• Buffer capacity is maximal for given concentrations
• Buffer spontaneously decomposes
• Buffer becomes neutralized

Correct Answer: Buffer capacity is maximal for given concentrations

Q43. Which of the following is true for polyprotic buffers used in formulations?

• They can provide buffering across multiple pH ranges corresponding to each pKa
• They have only one effective pH
• They are always unstable
• They cannot be used with ionic drugs

Correct Answer: They can provide buffering across multiple pH ranges corresponding to each pKa

Q44. In clinical formulations, why avoid buffers that strongly interact with metal ions?

• Metal chelation can alter drug bioavailability and stability
• Interaction only changes smell
• Metal ions always stabilize APIs
• Chelation increases buffer capacity beneficially

Correct Answer: Metal chelation can alter drug bioavailability and stability

Q45. Which buffer system is often used in gel formulations for skin due to mild pH?

• Hydrochloric acid buffer
• Phosphate or citrate buffer adjusted to skin pH
• Strong alkaline buffer
• Concentrated acetic acid

Correct Answer: Phosphate or citrate buffer adjusted to skin pH

Q46. Which measurement confirms correct buffer preparation in the lab?

• Visual inspection only
• Accurate pH measurement and ionic strength control
• Smell test
• Measuring refractive index only

Correct Answer: Accurate pH measurement and ionic strength control

Q47. For Henderson-Hasselbalch use, which concentration forms are plugged into the equation?

• Molar concentrations (or activities) of conjugate base [A-] and acid [HA]
• Only mass percentages
• Partial pressures
• Dielectric constants

Correct Answer: Molar concentrations (or activities) of conjugate base [A-] and acid [HA]

Q48. A buffer designed for chromatography must consider which additional factor?

• Buffer volatility and compatibility with detectors
• Only taste
• Buffer must be colored
• pH is irrelevant in chromatography

Correct Answer: Buffer volatility and compatibility with detectors

Q49. Which of the following best describes the “common ion effect” in buffers?

• Adding a common ion shifts the equilibrium, reducing solubility or altering dissociation
• Common ion increases the ionization of water dramatically
• Common ion effect heats the solution
• Common ion eliminates the need for pKa

Correct Answer: Adding a common ion shifts the equilibrium, reducing solubility or altering dissociation

Q50. When adjusting buffer pH during formulation scale-up, what must be re-evaluated?

• Only the pKa of the buffer
• Concentrations, ionic strength, temperature effects, and pH meter calibration
• Only the container material
• Color of the batch

Correct Answer: Concentrations, ionic strength, temperature effects, and pH meter calibration

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com