Acidic Buffers

An acidic buffer is a solution that resists changes in pH when a small amount of acid is added to it. It consists of a weak acid and its conjugate base, which can react with the added acid to maintain a relatively constant pH. In order for a pair of solutions to act as an acidic buffer, both the weak acid and its conjugate base must be present.

Pairs of Solutions

Let's examine each pair of solutions to determine if they can act as acidic buffers:

A. H2CO3 and Na2CO3
- H2CO3 is a weak acid (carbonic acid) and Na2CO3 is its conjugate base (sodium carbonate).
- This pair can act as an acidic buffer as it contains both a weak acid and its conjugate base.

B. H3PO4 and Na3PO4
- H3PO4 is a weak acid (phosphoric acid) and Na3PO4 is its conjugate base (sodium phosphate).
- This pair can act as an acidic buffer as it contains both a weak acid and its conjugate base.

C. HClO4 and NaClO4
- HClO4 is a strong acid (perchloric acid) and NaClO4 is its conjugate base (sodium perchlorate).
- This pair cannot act as an acidic buffer because the acid, HClO4, is a strong acid and does not readily dissociate to form its conjugate base.

D. CH3COOH and CH3COONa
- CH3COOH is a weak acid (acetic acid) and CH3COONa is its conjugate base (sodium acetate).
- This pair can act as an acidic buffer as it contains both a weak acid and its conjugate base.

Conclusion

The pair of solutions that is not an acidic buffer is C. HClO4 and NaClO4. It does not contain a weak acid and its conjugate base.