pKa ladder — NCERT valuespKa सीढ़ी — NCERT मानpKa ladder — NCERT values
Class 12 Chemistry · Chapter 8 · interactive diagram
Parts and what they mean
- Hydrochloric acid, pKa = –7.0 (हाइड्रोक्लोरिक अम्ल, pKa = –7.0) — A strong mineral acid — far stronger than any carboxylic acid.
- Trifluoroacetic acid, pKa = 0.23 (ट्राइफ़्लुओरोऐसीटिक अम्ल, pKa = 0.23) — The strongest carboxylic acid: three F atoms withdraw electrons (–I).
- 4-Nitrobenzoic acid, pKa = 3.41 (4-नाइट्रोबेंज़ोइक अम्ल, pKa = 3.41) — –NO₂ (electron-withdrawing) stabilises the carboxylate → stronger than benzoic acid.
- Benzoic acid, pKa = 4.19 (बेंज़ोइक अम्ल, pKa = 4.19) — Stronger than acetic acid: –COOH is attached to a more electronegative sp² carbon.
- 4-Methoxybenzoic acid, pKa = 4.46 (4-मेथॉक्सीबेंज़ोइक अम्ल, pKa = 4.46) — –OCH₃ (electron-donating) destabilises the carboxylate → weaker than benzoic acid.
- Acetic acid, pKa = 4.76 (ऐसीटिक अम्ल, pKa = 4.76) — The +I methyl group makes it weaker than formic and benzoic acids.
- Phenol, pKa = 10 (फ़ीनॉल, pKa = 10) — Phenoxide is less stabilised than carboxylate.
- Ethanol, pKa ≈ 16 (एथेनॉल, pKa ≈ 16) — Ethoxide has no resonance stabilisation at all.
- Strong acids: pKa < 1 (प्रबल अम्ल: pKa < 1) — NCERT classification by pKa.
- Moderately strong acids: pKa 1 to 5 (मध्यम प्रबल अम्ल: pKa 1 से 5) — Most carboxylic acids fall here.
- Weak acids: pKa 5 to 15 (दुर्बल अम्ल: pKa 5 से 15) — Phenol (10) lies here.
- Extremely weak acids: pKa > 15 (अत्यंत दुर्बल अम्ल: pKa > 15) — Ethanol (≈16) lies here.
- pKa = –log Ka (pKa = –log Ka) — Each unit of pKa is a factor of 10 in Ka.
Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake