Question

Match the following carboxylic acids with their pKa values.

• A. A-I, B-I, C-III
• B. A-II, B-III, C-I
• C. A-I, B-III, C-II
• D. A-II, B-I, C-III

Hint:

To determine the relative acidity of carboxylic acids, consider the inductive and resonance effects. Strong electron-withdrawing groups like -CF$_3$ decrease the pKa, making the acid stronger.

Answer 1

The Correct Option is B

We are given three carboxylic acids and their corresponding pKa values, and we need to correctly match them. 

Step 1: Understanding pKa values
The pKa value of an acid indicates its acidity; lower pKa values correspond to stronger acids.
- Acetic acid (CH$_3$COOH) has a known pKa value of 4.76.
- Benzoic acid (C$_6$H$_5$COOH) has a pKa value of 4.19.
- Trifluoroacetic acid (CF$_3$COOH) is a highly acidic carboxylic acid due to the strong electron-withdrawing effect of fluorine atoms, and its pKa value is 0.23.
Step 2: Matching the values
From the given pKa values, we match:
- $A$ (CH$_3$COOH) $\rightarrow$ $II$ (4.76) 
- $B$ (C$_6$H$_5$COOH) $\rightarrow$ $III$ (4.19)
- $C$ (CF$_3$COOH) $\rightarrow$ $I$ (0.23)
Thus, the correct matching is A-II, B-III, C-I, which corresponds to option (2).