Chemistry - GOC Question with Solution | TestHub
Which of the following is the correct order of acidic strength.
Options:
Answer:
Solution:
Question Explanation:
The question is asking about the correct decreasing order (strongest to weakest) of acidic strength for the four given compounds.
Concept:
Acidity of Organic Compounds, Substituent Effects (Electron-Withdrawing Groups (EWG), Inductive Effect, Resonance/Mesomeric Effect , Stability of Conjugate Base (Anion), Comparison of Acidity (Carboxylic Acids vs. Phenols vs. Inorganic Acids)
Solution:
Acidic strength is determined by the stability of the conjugate base formed after losing a proton H+ . Greater stability means a stronger acid.
1. 2,4-Dinitrobenzoic Acid: This is Benzoic Acid substituted with two strong Electron-Withdrawing Groups (EWG), the nitro (-NO2 ) groups, at the ortho (2) and para (4) positions. Strongest Acid.
2. Benzoic Acid: The carboxylate anion is highly stabilized by resonance, making it generally much stronger than phenols and slightly stronger than Carbonic Acid.
3. Carbonic Acid (H2CO3 ): This inorganic acid has a pKa value around 6.35. It is typically stronger than simple phenols.
This decreasing order is: 2,4-Dinitrobenzoic Acid > Benzoic Acid > Carbonic Acid (H2CO3 ) > Phenol
This order matches Option A.