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How many of the following compounds dissolve in aqueous NaOH solution? (1) Phenol (2) Cyclohexanol (3) Cyclohexanecarboxylic acid (4) 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid) (5) Benzene (6) Benzyl alcohol (7) Benzenesulfonic acid
- 3
- 4
- 5
- 6
Correct answer: 4
Solution
NaOH dissolves compounds that are sufficiently acidic: (1) Phenol - YES (pKa ~10, forms sodium phenoxide); (2) Cyclohexanol - NO (pKa ~16, too weakly acidic for aqueous NaOH); (3) Cyclohexanecarboxylic acid - YES (carboxylic acid, pKa ~4.8); (4) Squaric acid - YES (pKa1 ~1.5, highly acidic due to aromatic resonance in the dianion); (5) Benzene - NO (inert to NaOH); (6) Benzyl alcohol - NO (pKa ~15, simple benzylic alcohol, not acidic enough); (7) Benzenesulfonic acid - YES (strong acid, instantly neutralised by NaOH). Total = 4.
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