To analyze the reaction \( \text{HCl} + \text{H}_2\text{O} \rightarrow \text{Cl}^- + \text{H}_3\text{O}^+ \), we need to determine which species acts as the acid and which acts as the base.
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Identify the acid and base:
- HCl donates a proton (\( \text{H}^+ \)) and forms \( \text{Cl}^- \). Thus, \( \text{HCl} \) acts as an acid.
- H2O accepts a proton to form \( \text{H}_3\text{O}^+ \). Thus, \( \text{H2O} \) acts as a base.
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Identify conjugate pairs:
- The conjugate base of an acid is what remains after the acid donates a proton.
- Here, after \( \text{HCl} \) donates a proton, it becomes \( \text{Cl}^- \). Hence, \( \text{Cl}^- \) is the conjugate base of \( \text{HCl} \).
- After \( \text{H}_2\text{O} \) accepts a proton, it becomes \( \text{H}_3\text{O}^+ \), which is the conjugate acid of \( \text{H}_2\text{O} \).
Now, we can evaluate each statement:
A. HCl is an acid, and H3O\(^+\) is its conjugate base. (Incorrect, because \( \text{H}_3\text{O}^+ \) is the conjugate acid of \( \text{H}_2\text{O} \), not the conjugate base of \( \text{HCl} \).)
B. HCl is an acid, and Cl\(^-\) is its conjugate base. (Correct, \( \text{HCl} \) is the acid and \( \text{Cl}^- \) is indeed its conjugate base.)
C. H2O is an acid, and H3O\(^+\) is its conjugate base. (Incorrect, because while \( \text{H}_2\text{O} \) acts as a base in this reaction, \( \text{H}_3\text{O}^+ \) is its conjugate acid, not base.)
D. H2O is an acid, and Cl\(^-\) is its conjugate base. (Incorrect, \( \text{H}_2\text{O} \) acts as a base, and \( \text{Cl}^- \) is not its conjugate base.)
The correct answer is B. HCl is an acid, and Cl\(^-\) is its conjugate base.