A student attempted to separate a 5.00 g crude mixture containing benzoic acid (2.00 g), 2-naphthol (1.50 g, pKa = 9.5), and naphthalene (1.50 g) using the following procedure recorded in the laboratory notebook:
1. Dissolved the mixture in 50 mL diethyl ether.
2. Added 50 mL of 6 M HCl, shook, and removed the bottom aqueous layer (Fraction 1).
3. Added 50 mL of 1 M NaHCO₃ to the ether layer, separated the aqueous layer (Fraction 2).
4. Added 50 mL of 1 M NaOH to the remaining ether layer, separated the aqueous layer (Fraction 3).
5. Evaporated the ether to obtain 1.20 g of a solid labeled “naphthalene fraction” that melted over a broad range.
6. Acidified Fractions 2 and 3 separately with concentrated HCl, yielding precipitates of 1.10 g and 2.40 g, respectively.
Total mass recovered: 4.70 g.
(a) Based on acid–base chemistry, identify which compound(s) should have been extracted into Fraction 1. Evaluate whether using 6 M HCl was appropriate and explain your reasoning.
(b) Determine the principal procedural flaw that likely caused contamination of the "naphthalene fraction." Propose a revised sequence of extractions—including reagent strengths—that would enhance selectivity.
(c) Assuming ideal partitioning and using a partition coefficient of 25 for naphthalene between ether and water, calculate the theoretical maximum mass of naphthalene that would remain in the ether layer after the corrected extraction sequence described in part (b). Show all work.
(d) Suggest two additional laboratory techniques, other than repeating the extraction, that could further purify the recovered naphthalene. For each technique, briefly explain the property difference it exploits.