Question

Identify $\text{base}_2$ for the following equation according to Br\o{}nsted--Lowry theory: \[HCl_{(aq)} + H_2O_{(l)} \rightleftharpoons H_3O^+_{(aq)} + Cl^-_{(aq)}\]}

• A. $H_3O^+_{(aq)}$
• B. $H_2O_{(l)}$
• C. $Cl^-_{(aq)}$
• D. $HCl_{(aq)}$

Hint:

Conjugate acid--base pairs always differ by exactly one $H^+$ ion. Acid $\rightarrow$ Base$_2$ (loses $H^+$); Base $\rightarrow$ Acid$_2$ (gains $H^+$).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
According to Brønsted–Lowry theory, an acid is a proton (\( H^+ \)) donor and a base is a proton acceptor.
A reaction involves two conjugate acid-base pairs.
Step 2: Detailed Explanation:
In the given reaction: \( HCl + H_2O \rightarrow H_3O^+ + Cl^- \).
1. \( HCl \) gives away a proton to become \( Cl^- \). Thus, \( HCl \) is Acid\(_1\) and \( Cl^- \) is Base\(_1\).
2. \( H_2O \) accepts a proton to become \( H_3O^+ \). Thus, \( H_2O \) is Base\(_2\) and \( H_3O^+ \) is Acid\(_2\).
The question asks for Base\(_2\).
Step 3: Final Answer:
Base\(_2\) is \( H_2O_{(l)} \).
This matches Option (B).