Consider the reaction below.

[tex]\[
HI + H_2O \rightarrow H_3O^+ + I^-
\][/tex]

Which is an acid-conjugate base pair?

A. [tex]\( HI \)[/tex] and [tex]\( H_2O \)[/tex]

B. [tex]\( H_2O \)[/tex] and [tex]\( H_3O^+ \)[/tex]

C. [tex]\( H_3O^+ \)[/tex] and [tex]\( I^- \)[/tex]

D. [tex]\( HI \)[/tex] and [tex]\( I^- \)[/tex]



Answer :

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

[tex]\[ HI + H_2O \rightarrow H_3O^+ + I^- \][/tex]

we will analyze the species involved:

1. Identify the roles:
- [tex]\( HI \)[/tex] donates a proton ([tex]\( H^+ \)[/tex]) and becomes [tex]\( I^- \)[/tex].
- [tex]\( H_2O \)[/tex] accepts a proton ([tex]\( H^+ \)[/tex]) and becomes [tex]\( H_3O^+ \)[/tex].

2. Definition check:
- An acid is a species that donates a proton ([tex]\( H^+ \)[/tex]).
- A conjugate base is the species that remains after the acid has donated a proton.
- Therefore, an acid and its conjugate base are related to each other by the loss of a single proton.

3. Identify pairs:
- [tex]\( HI \)[/tex] is an acid since it donates a proton to form [tex]\( I^- \)[/tex]. Therefore, [tex]\( HI \)[/tex] and [tex]\( I^- \)[/tex] form an acid-conjugate base pair.
- [tex]\( H_2O \)[/tex] accepts a proton to become [tex]\( H_3O^+ \)[/tex]. So, [tex]\( H_2O \)[/tex] and [tex]\( H_3O^+ \)[/tex] also form an acid-conjugate base pair.

Now, we carefully match these identified pairs with the given options:

1. [tex]\( HI \)[/tex] and [tex]\( H_2O \)[/tex]
- This is not an acid-conjugate base pair.
2. [tex]\( H_2O \)[/tex] and [tex]\( H_3O^+ \)[/tex]
- This is a correct acid-conjugate base pair.
3. [tex]\( H_3O^+ \)[/tex] and [tex]\( I^- \)[/tex]
- These do not form an acid-conjugate base pair.
4. [tex]\( HI \)[/tex] and [tex]\( I^- \)[/tex]
- This is a correct acid-conjugate base pair.

Among the options, we are looking for the pair involving [tex]\( HI \)[/tex] and [tex]\( I^- \)[/tex].

Thus, the correct answer is:

[tex]\[ \boxed{HI \text{ and } I^{-}} \][/tex]

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