Question

Which of the following carboxylic acid has the least pKa value among all? 

Hint:

A lower pKa value means a stronger acid. Formic acid (HCOOH) has the lowest pKa among carboxylic acids because it lacks an electron-donating alkyl group.

Answer 1

Step 1: Understanding pKa and Acidity 
- The pKa value is the negative logarithm of the acid dissociation constant (\( K_a \)), which measures the strength of an acid.
- A lower pKa value indicates a stronger acid, meaning the acid ionizes more easily in solution. 
Step 2: Comparing Carboxylic Acids 
- Carboxylic acids (\( R-COOH \)) have different pKa values depending on the electron-withdrawing or electron-donating nature of the substituent group (\( R \)).
- Formic acid (HCOOH) has the lowest pKa value among carboxylic acids because:
- It lacks an alkyl group, so there is no electron-donating effect to stabilize the carboxylate ion.
- It is the simplest carboxylic acid, making it the strongest among its homologs. 
Step 3: Conclusion 
- Since HCOOH (Formic Acid) has the least pKa value, it is the strongest carboxylic acid among common carboxylic acids.