Questions about Buffers
BUFFERS – MULTIPLE-CHOICE QUESTIONS
1. What is a buffer solution?
A) A solution that conducts electricity
B) A solution that changes pH easily
C) A solution that resists changes in pH upon addition of small amounts of acid or base
D) A saturated salt solution
E) A neutral solution
2. Which of the following is a common acidic buffer system?
A) NH₃/NH₄Cl
B) HCl/NaCl
C) CH₃COOH/CH₃COONa
D) NaOH/NaCl
E) Na₂CO₃/NaOH
3. A basic buffer solution is made by combining:
A) A weak base and its conjugate acid
B) A strong base and strong acid
C) A weak acid and strong base
D) A strong base and salt
E) A neutral salt and acid
4. Which of the following is not a buffer solution?
A) CH₃COOH/CH₃COONa
B) NH₄OH/NH₄Cl
C) HCl/NaCl
D) H₂CO₃/NaHCO₃
E) HPO₄²⁻/H₂PO₄⁻
5. What happens when a small amount of strong acid is added to a buffer?
A) The pH increases sharply
B) The pH becomes exactly 7
C) The buffer neutralizes the acid and pH changes slightly
D) The solution becomes saturated
E) The buffer decomposes
6. Which of the following pairs could make a buffer solution?
A) HNO₃/NaNO₃
B) HCl/KCl
C) CH₃COOH/NaCH₃COO
D) NaOH/NaCl
E) H₂SO₄/Na₂SO₄
7. Buffers are most effective when the ratio of acid to conjugate base is:
A) 10:1
B) 1:10
C) 1:1
D) 100:1
E) 1:100
8. Which component in a buffer neutralizes added acid?
A) Weak acid
B) Strong acid
C) Conjugate base
D) Strong base
E) Water
9. What is the main function of a buffer in biological systems?
A) Promote protein synthesis
B) Maintain constant temperature
C) Stabilize pH
D) Catalyze enzyme reactions
E) Facilitate respiration
10. The Henderson–Hasselbalch equation is used to calculate:
A) Molarity
B) Reaction rate
C) pH of a buffer
D) Buffer volume
E) Salt concentration
11. What is the formula for the Henderson–Hasselbalch equation for acidic buffers?
A) pH = pKa + log([base]/[acid])
B) pH = -log[H⁺]
C) pH = pKa - log([acid]/[base])
D) pH = pKb + log([acid]/[base])
E) pH = pKa + [base] × [acid]
12. A buffer with pKa = 4.75 is most effective at pH:
A) 1.5
B) 3.0
C) 4.75
D) 6.5
E) 8.0
13. Which of the following would act as a basic buffer?
A) CH₃COOH/CH₃COONa
B) HCl/NaCl
C) NH₃/NH₄Cl
D) HNO₃/KNO₃
E) NaOH/Na₂SO₄
14. Buffer capacity is defined as the amount of:
A) Salt present in buffer
B) Base needed to completely neutralize the acid
C) Acid or base the buffer can absorb without significant pH change
D) Water in buffer
E) Heat released upon mixing
15. If a buffer has [acid] = [conjugate base], then:
A) pH = 0
B) pH = 14
C) pH = pKa
D) pH = pKb
E) Buffer is destroyed
16. What is the best choice of buffer if the desired pH is 9.25?
A) Acetic acid/acetate (pKa = 4.75)
B) Ammonia/ammonium (pKa ≈ 9.25)
C) H₂CO₃/HCO₃⁻ (pKa ≈ 6.1)
D) HCl/Cl⁻
E) H₃PO₄/H₂PO₄⁻
17. Buffers are least effective when:
A) pH = pKa
B) pH differs greatly from pKa
C) Acid/base ratio is 1
D) Used in small volume
E) Diluted
18. The blood buffer system involves primarily:
A) CH₃COOH/CH₃COONa
B) NH₃/NH₄⁺
C) H₂CO₃/HCO₃⁻
D) HCl/KCl
E) NaOH/Na₂SO₄
19. A buffer maintains pH by reacting with:
A) Only acids
B) Only bases
C) Both acids and bases
D) Water
E) Gases only
20. Why are buffers important in analytical chemistry?
A) To dissolve metals
B) To calibrate thermometers
C) To prevent drastic pH changes in reactions
D) To remove impurities
E) To initiate combustion
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ANSWER KEY
1. C – A buffer resists changes in pH upon the addition of small amounts of acid or base.
2. C – CH₃COOH/CH₃COONa is an acidic buffer made of a weak acid and its salt.
3. A – A basic buffer is a mixture of a weak base and its conjugate acid.
4. C – HCl is a strong acid, and NaCl is a neutral salt; this mixture does not form a buffer.
5. C – The buffer reacts with added acid to minimize the change in pH.
6. C – CH₃COOH (weak acid) and NaCH₃COO (its salt) form a buffer.
7. C – Buffers are most effective when the acid/base ratio is close to 1:1.
8. C – The conjugate base neutralizes added H⁺ ions.
9. C – Buffers help biological systems maintain constant pH, critical for enzyme function and homeostasis.
10. C – The Henderson–Hasselbalch equation helps calculate the pH of buffer solutions.
11. A – The equation is: pH = pKa + log([conjugate base]/[acid]).
12. C – A buffer is most effective at a pH equal to its pKa.
13. C – NH₃/NH₄Cl is a basic buffer system.
14. C – Buffer capacity is the amount of acid/base a buffer can neutralize before a significant pH shift occurs.
15. C – When [acid] = [base], pH = pKa by definition of the Henderson–Hasselbalch equation.
16. B – A buffer works best when pKa is close to the desired pH; ammonia’s conjugate acid has a pKa around 9.25.
17. B – When the pH is far from the pKa, the buffer is less effective.
18. C – The primary buffer system in human blood is H₂CO₃/HCO₃⁻ (carbonic acid/bicarbonate).
19. C – Buffers work by neutralizing
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