CH3COOH(aq) + OH-(aq) ↔ CH3COO-(aq) + H2O(l) In the reaction above ,CH3COO-(aq) is

Analysis

This question tests your understanding of the Brønsted-Lowry Theory of Acids and Bases. According to this theory, an acid is a proton ($H^+$) donor, and a base is a proton acceptor. When an acid loses a proton, it forms a conjugate base. When a base gains a proton, it forms a conjugate acid.

Concept Explanation

In any acid-base reaction, we look at the relationship between the reactants and the products:

1. The Acid: $CH_3COOH$ (ethanoic acid) donates a proton ($H^+$) to the $OH^-$ ion.
2. The Base: $OH^-$ (hydroxide ion) accepts the proton.
3. The Conjugate Base: After $CH_3COOH$ loses its proton, it becomes $CH_3COO^-$ (ethanoate ion). Because it is the species left behind after the acid has donated its proton, it is called the conjugate base.
4. The Conjugate Acid: After $OH^-$ accepts the proton, it becomes $H_2O$. Because it is the species formed after the base has accepted a proton, it is called the conjugate acid.

Step-by-Step Solution

• Step 1: Identify the reactant that loses the proton. $CH_3COOH \rightarrow CH_3COO^- + H^+$. Since $CH_3COOH$ is the acid, the resulting $CH_3COO^-$ is its conjugate base.
• Step 2: Identify the reactant that gains the proton. $OH^- + H^+ \rightarrow H_2O$. Since $OH^-$ is the base, the resulting $H_2O$ is its conjugate acid.
• Step 3: Match the species in the question. The question asks for the identity of $CH_3COO^-$. Based on our analysis, it is the conjugate base of $CH_3COOH$.

Conclusion

Exam Tip

Remember the "minus one" rule: A conjugate base is always what remains of an acid after it has lost one $H^+$. If you are ever confused, just look at the pair: the one with one less hydrogen is the conjugate base!