Which one of the following pairs of solutions is not an acidic buffer?

Chemistry
1

Which one of the following pairs of solutions is not an acidic buffer? (a) \mathrm{CH}_{3} \mathrm{COOH} and \mathrm{CH}_{3} \mathrm{COONa} (b) \mathrm{H}_{2} \mathrm{CO}_{3} and \mathrm{Na}_{2} \mathrm{CO}_{3} (c) \mathrm{H}_{3} \mathrm{PO}_{4} and \mathrm{Na}_{3} \mathrm{PO}_{4} (d) \mathrm{HClO}_{4} and \mathrm{NaClO}_{4}

2

Which one of the following pairs of solutions is not an acidic buffer?

(a) \mathrm{CH}_{3} \mathrm{COOH} and \mathrm{CH}_{3} \mathrm{COONa}

(b) \mathrm{H}_{2} \mathrm{CO}_{3} and \mathrm{Na}_{2} \mathrm{CO}_{3}

(c) \mathrm{H}_{3} \mathrm{PO}_{4} and \mathrm{Na}_{3} \mathrm{PO}_{4}

(d) \mathrm{HClO}_{4} and \mathrm{NaClO}_{4}

Answer: To determine which pair of solutions is not an acidic buffer, we need to understand what constitutes an acidic buffer.

Acidic Buffer Definition: An acidic buffer solution is a mixture of a weak acid and its conjugate base (typically a salt). This combination helps maintain a relatively constant pH when small amounts of acid or base are added.

Analysis of Each Pair:

  1. (a) \mathrm{CH}_{3} \mathrm{COOH} and \mathrm{CH}_{3} \mathrm{COONa}

    • Explanation: This pair includes acetic acid (\mathrm{CH}_{3} \mathrm{COOH}), a weak acid, and sodium acetate (\mathrm{CH}_{3} \mathrm{COONa}), the salt of its conjugate base (\mathrm{CH}_{3} \mathrm{COO}^-).
    • Conclusion: This is an acidic buffer.

  2. (b) \mathrm{H}_{2} \mathrm{CO}_{3} and \mathrm{Na}_{2} \mathrm{CO}_{3}

    • Explanation: This pair includes carbonic acid (\mathrm{H}_{2} \mathrm{CO}_{3}), a weak acid, and sodium carbonate (\mathrm{Na}_{2} \mathrm{CO}_{3}), a salt that provides the conjugate base (\mathrm{CO}_{3}^{2-}).
    • Conclusion: This is an acidic buffer.

  3. (c) \mathrm{H}_{3} \mathrm{PO}_{4} and \mathrm{Na}_{3} \mathrm{PO}_{4}

    • Explanation: This pair includes phosphoric acid (\mathrm{H}_{3} \mathrm{PO}_{4}), a weak acid. However, sodium phosphate (\mathrm{Na}_{3} \mathrm{PO}_{4}) dissociates to provide \mathrm{PO}_{4}^{3-}, which is a conjugate base of the second dissociation step of phosphoric acid. Generally, \mathrm{NaH}_{2} \mathrm{PO}_{4} or \mathrm{Na}_{2} \mathrm{HPO}_{4} would form an acidic buffer with \mathrm{H}_{3} \mathrm{PO}_{4}.
    • Conclusion: This is not a typical acidic buffer but rather moves towards a basic buffer.

  4. (d) \mathrm{HClO}_{4} and \mathrm{NaClO}_{4}

    • Explanation: This pair includes perchloric acid (\mathrm{HClO}_{4}), which is a strong acid, and sodium perchlorate (\mathrm{NaClO}_{4}), the salt of its conjugate base (\mathrm{ClO}_{4}^-).
    • Conclusion: Since \mathrm{HClO}_{4} is a strong acid, it does not form a buffer because strong acids completely dissociate in water, not maintaining a buffer system.

Verdict:

The correct answer is option (d) \mathrm{HClO}_{4} and \mathrm{NaClO}_{4} because this pair does not form an acidic buffer due to the presence of a strong acid.