Question

Which of the following pairs could form a buffer?

1) C6H5COOH and C6H5COONa
2) HCl and NaCl
3) HCl and NaOH
4) NH₃ and H3BO₃

Answer 1

The combination C6H5COOH (benzoic acid) and C6H5COONa (sodium benzoate) can form a buffer because they consist of a weak acid and its conjugate salt. Other combinations listed involve either strong acids or bases that do not form buffers or do not share a common ion necessary for buffer formation.

Step-by-step explanation:

The student has asked which pairs could form a buffer. A buffer is formed by a mixture of a weak acid or a weak base and its salt with a strong acid or base. This mixture is able to resist changes in pH when small amounts of acid or alkali are added.

To identify potential buffers from the list:

1. C6H5COOH (benzoic acid, a weak acid) and C6H5COONa (sodium benzoate, the salt of benzoic acid) would make a buffer.
2. HCl and NaCl would not form a buffer as HCl is a strong acid, and NaCl is a neutral salt that doesn't affect the pH.
3. HCl and NaOH would not form a buffer since both are strong electrolytes and completely dissociate in water, leaving no weak component to establish a buffer system.
4. NH₃ (ammonia, a weak base) and H3BO3 (boric acid, a weak acid) would not typically form a buffer because they don't share a common ion. A buffer system usually consists of a weak acid and its conjugate base or a weak base and its conjugate acid.