Consider the reaction below.

[tex]\[ HF + H_2O \rightarrow H_3O^+ + F^- \][/tex]

Which is an acid-conjugate base pair?

A. HF and [tex]\( H_3O^+ \)[/tex]

B. HF and [tex]\( F^- \)[/tex]

C. [tex]\( H_2O \)[/tex] and HF

D. [tex]\( H_2O \)[/tex] and [tex]\( F^- \)[/tex]



Answer :

To determine the acid-conjugate base pair in the given reaction:

[tex]\[ HF + H_2O \rightarrow H_3O^+ + F^- \][/tex]

we first need to understand the concept of an acid-conjugate base pair. According to the Brønsted-Lowry theory of acids and bases, an acid is a species that donates a proton (H^+) and a base is a species that accepts a proton. A conjugate base is what remains after the acid has donated its proton, and a conjugate acid is what forms when the base accepts a proton.

Let's breakdown the given reaction:
1. HF (hydrofluoric acid) donates a proton to the water molecule.
[tex]\[ HF \rightarrow F^- + H^+ \][/tex]
Hence, HF is acting as an acid, and F^- is its conjugate base since it is what remains after HF donates a proton.

2. H_2O (water) accepts a proton from HF.
[tex]\[ H_2O + H^+ \rightarrow H_3O^+ \][/tex]
Here, H_2O is acting as a base, and H_3O^+ (hydronium ion) is its conjugate acid since it is the result of H_2O accepting a proton.

Given these interactions:
- HF and F^- form an acid-conjugate base pair, as HF donates a proton becoming F^-.
- H_2O and H_3O^+ form a base-conjugate acid pair, as H_2O accepts a proton becoming H_3O^+.

Therefore, the correct acid-conjugate base pair in the reaction is:

[tex]\[ \boxed{\text{HF and } F^-} \][/tex]

So, the correct choice is:
- HF and [tex]\( F^- \)[/tex].