#Chemistry
#onAcid-Base Equilibrium
1. Which of the following statements best describes a Bronsted-Lowry acid?
- A) A substance that donates a pair of electrons.
- B) A substance that donates a proton (H+).
- C) A substance that accepts a proton (H+).
- D) A substance that dissociates completely in water.
Answer: B) A substance that donates a proton (H+)
Explanation: In the Bronsted-Lowry theory, an acid is defined as a proton donor, while a base is a proton acceptor.
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2. If a solution has a pH of 3, it is considered:
- A) Neutral
- B) Slightly acidic
- C) Highly acidic
- D) Basic
Answer: C) Highly acidic
Explanation: The pH scale ranges from 0 to 14, with values below 7 considered acidic. A pH of 3 indicates a strongly acidic solution.
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3. What is the pH of a solution if the concentration of H+ ions is 1 x 10^-5 M?
- A) 5
- B) 7
- C) 9
- D) 12
Answer: A) 5
Explanation: pH is calculated using the formula pH = -log[H+]. With an H+ concentration of 1 x 10^-5 M, the pH is 5.
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4. In the reaction NH₃ + H₂O ⇌ NH₄⁺ + OH⁻, which species acts as the Bronsted-Lowry base?
- A) NH₃
- B) H₂O
- C) NH₄⁺
- D) OH⁻
Answer: A) NH₃
Explanation: In this reaction, NH₃ accepts a proton (H+) from H₂O, acting as a Bronsted-Lowry base.
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5. Which of the following solutions would be considered a buffer?
- A) HCl and NaCl
- B) CH₃COOH and CH₃COONa
- C) NaOH and NaCl
- D) H₂SO₄ and HCl
Answer: B) CH₃COOH and CH₃COONa
Explanation: A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). Acetic acid (CH₃COOH) and sodium acetate (CH₃COONa) form a buffer.
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6. If the pKa of acetic acid is 4.76, at what pH is the concentration of acetic acid equal to the concentration of acetate ion?
- A) 3.76
- B) 4.76
- C) 5.76
- D) 7.00
Answer: B) 4.76
Explanation: According to the Henderson-Hasselbalch equation, pH = pKa when the concentrations of the acid and its conjugate base are equal.
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7. Which of the following is the conjugate base of H₂CO₃?
- A) HCO₃⁻
- B) CO₃²⁻
- C) OH⁻
- D) H₂O
Answer: A) HCO₃⁻
Explanation: When H₂CO₃ (carbonic acid) loses one proton (H+), it forms HCO₃⁻ (bicarbonate), which is its conjugate base.
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8. What happens to the pH of a buffer solution if a small amount of a strong acid is added?
- A) pH increases
- B) pH decreases significantly
- C) pH remains nearly constant
- D) pH becomes neutral (7)
Answer: C) pH remains nearly constant
Explanation: Buffers resist changes in pH, so the pH of the solution remains relatively stable even if a small amount of strong acid is added.
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9. Which of the following pairs could act as a buffer in aqueous solution?
- A) HCl and Cl⁻
- B) NaOH and NaCl
- C) H₂CO₃ and NaHCO₃
- D) HNO₃ and NO₃⁻
Answer: C) H₂CO₃ and NaHCO₃
Explanation: Carbonic acid (H₂CO₃) and bicarbonate (NaHCO₃) form a buffer system, often found in natural systems like blood.
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10. Which of the following best explains why the pH of pure water is 7 at 25°C?
- A) Water is a neutral substance with equal concentrations of H+ and OH- ions.
- B) Water does not ionize at all.
- C) Water is only slightly acidic at room temperature.
- D) The pH scale is based on water’s natural acidity.
Answer: A) Water is a neutral substance with equal concentrations of H+ and OH- ions.
Explanation: At 25°C, pure water has equal concentrations of H+ and OH- ions (1 x 10^-7 M), resulting in a neutral pH of 7.
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#onAcid-Base Equilibrium
1. Which of the following statements best describes a Bronsted-Lowry acid?
- A) A substance that donates a pair of electrons.
- B) A substance that donates a proton (H+).
- C) A substance that accepts a proton (H+).
- D) A substance that dissociates completely in water.
Answer: B) A substance that donates a proton (H+)
Explanation: In the Bronsted-Lowry theory, an acid is defined as a proton donor, while a base is a proton acceptor.
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2. If a solution has a pH of 3, it is considered:
- A) Neutral
- B) Slightly acidic
- C) Highly acidic
- D) Basic
Answer: C) Highly acidic
Explanation: The pH scale ranges from 0 to 14, with values below 7 considered acidic. A pH of 3 indicates a strongly acidic solution.
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3. What is the pH of a solution if the concentration of H+ ions is 1 x 10^-5 M?
- A) 5
- B) 7
- C) 9
- D) 12
Answer: A) 5
Explanation: pH is calculated using the formula pH = -log[H+]. With an H+ concentration of 1 x 10^-5 M, the pH is 5.
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4. In the reaction NH₃ + H₂O ⇌ NH₄⁺ + OH⁻, which species acts as the Bronsted-Lowry base?
- A) NH₃
- B) H₂O
- C) NH₄⁺
- D) OH⁻
Answer: A) NH₃
Explanation: In this reaction, NH₃ accepts a proton (H+) from H₂O, acting as a Bronsted-Lowry base.
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5. Which of the following solutions would be considered a buffer?
- A) HCl and NaCl
- B) CH₃COOH and CH₃COONa
- C) NaOH and NaCl
- D) H₂SO₄ and HCl
Answer: B) CH₃COOH and CH₃COONa
Explanation: A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). Acetic acid (CH₃COOH) and sodium acetate (CH₃COONa) form a buffer.
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6. If the pKa of acetic acid is 4.76, at what pH is the concentration of acetic acid equal to the concentration of acetate ion?
- A) 3.76
- B) 4.76
- C) 5.76
- D) 7.00
Answer: B) 4.76
Explanation: According to the Henderson-Hasselbalch equation, pH = pKa when the concentrations of the acid and its conjugate base are equal.
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7. Which of the following is the conjugate base of H₂CO₃?
- A) HCO₃⁻
- B) CO₃²⁻
- C) OH⁻
- D) H₂O
Answer: A) HCO₃⁻
Explanation: When H₂CO₃ (carbonic acid) loses one proton (H+), it forms HCO₃⁻ (bicarbonate), which is its conjugate base.
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8. What happens to the pH of a buffer solution if a small amount of a strong acid is added?
- A) pH increases
- B) pH decreases significantly
- C) pH remains nearly constant
- D) pH becomes neutral (7)
Answer: C) pH remains nearly constant
Explanation: Buffers resist changes in pH, so the pH of the solution remains relatively stable even if a small amount of strong acid is added.
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9. Which of the following pairs could act as a buffer in aqueous solution?
- A) HCl and Cl⁻
- B) NaOH and NaCl
- C) H₂CO₃ and NaHCO₃
- D) HNO₃ and NO₃⁻
Answer: C) H₂CO₃ and NaHCO₃
Explanation: Carbonic acid (H₂CO₃) and bicarbonate (NaHCO₃) form a buffer system, often found in natural systems like blood.
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10. Which of the following best explains why the pH of pure water is 7 at 25°C?
- A) Water is a neutral substance with equal concentrations of H+ and OH- ions.
- B) Water does not ionize at all.
- C) Water is only slightly acidic at room temperature.
- D) The pH scale is based on water’s natural acidity.
Answer: A) Water is a neutral substance with equal concentrations of H+ and OH- ions.
Explanation: At 25°C, pure water has equal concentrations of H+ and OH- ions (1 x 10^-7 M), resulting in a neutral pH of 7.
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