Question

What is the pKa value of the given compound?

• A. \(\text{CH}_3\text{CH}_2\text{COOH}\)
• B. \(\text{ClCH}_2\text{COOH}\)
• C. \(\text{C}_6\text{H}_5\text{CH}_2\text{COOH}\)
• D. \(\text{HCOOH}\)

Hint:

When analyzing acids, remember that electron-withdrawing groups (like Cl) decrease the pKa, making the acid stronger.

Answer 1

The Correct Option is A

Step 1: Understanding pKa.
The pKa value of a compound gives insight into its acidity. The lower the pKa, the stronger the acid. In this case, we are asked to identify the compound with the correct pKa value.
Step 2: Analyzing the Options.
- (A) \(\text{CH}_3\text{CH}_2\text{COOH}\) is the correct compound as it is a simple carboxylic acid, and its pKa is approximately 4.8.
- (B) \(\text{ClCH}_2\text{COOH}\) is a carboxylic acid, but the electron-withdrawing chlorine group will lower the pKa slightly, making it more acidic than acetic acid.
- (C) \(\text{C}_6\text{H}_5\text{CH}_2\text{COOH}\) is a benzoic acid derivative, which has a slightly lower pKa than acetic acid.
- (D) \(\text{HCOOH}\) is formic acid, which has a lower pKa (~3.75), indicating a stronger acid than acetic acid.
Step 3: Conclusion.
The correct answer is (A) \(\text{CH}_3\text{CH}_2\text{COOH}\) as it has the pKa value closest to 4.8, typical for acetic acid.