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Which of the following pairs would form a buffer solution? (A) HCl(aq) / Cl⁻(aq) (B) H₂PO₄⁻(aq) / PO₄³⁻(aq) (C) H₂SO₄(aq) / HSO₄⁻(aq) (D) CH₃COOH(aq) / CH₃COO⁻(aq) - HSC - SSCE Chemistry - Question 9 - 2005 - Paper 1
Question 9
Which of the following pairs would form a buffer solution? (A) HCl(aq) / Cl⁻(aq) (B) H₂PO₄⁻(aq) / PO₄³⁻(aq) (C) H₂SO₄(aq) / HSO₄⁻(aq) (D) CH₃COOH(aq) / CH₃COO⁻(aq)
Worked Solution & Example Answer:Which of the following pairs would form a buffer solution? (A) HCl(aq) / Cl⁻(aq) (B) H₂PO₄⁻(aq) / PO₄³⁻(aq) (C) H₂SO₄(aq) / HSO₄⁻(aq) (D) CH₃COOH(aq) / CH₃COO⁻(aq) - HSC - SSCE Chemistry - Question 9 - 2005 - Paper 1
Step 1
Which of the following pairs would form a buffer solution?
Answer
To determine which pair can form a buffer solution, we need to remember that a buffer consists of a weak acid and its conjugate base or a weak base and its conjugate acid.
- Option A: HCl(aq) / Cl⁻(aq) - HCl is a strong acid and does not form a buffer.
- Option B: H₂PO₄⁻(aq) / PO₄³⁻(aq) - This pair consists of a weak acid (H₂PO₄⁻) and its conjugate base (PO₄³⁻), thus it forms a buffer solution.
- Option C: H₂SO₄(aq) / HSO₄⁻(aq) - H₂SO₄ is a strong acid and does not provide a stable buffer.
- Option D: CH₃COOH(aq) / CH₃COO⁻(aq) - This pair consists of acetic acid (weak acid) and its conjugate base (acetate ion), which forms a buffer solution.
Thus, the pairs that would form a buffer solution are option B and option D. However, based on the marking scheme, the correct answer for selection is D: CH₃COOH(aq) / CH₃COO⁻(aq).