2-methylbenzoic acid, naphthalene and magnesium chloride are present in a solid

Question

2-methylbenzoic acid, naphthalene and magnesium chloride are present in a solid mixture. Propose a detail separation scheme to isolate these three compounds as solids. Below is a list of reagents available in lab. You may use any of these given reagents (e.g., acids, bases) as needed in your separation scheme and you also have access to a solvent evaporator if a solvent must be evaporated, and a filtration apparatus to filter. Be specific in each reagent name and technique used in your separation scheme. The most efficient separation scheme will receive the most credit.

5. 2-methylbenzoic acid, naphthalene and magnesium chloride are present in a solid mixture. Propose a detail separation scheme to isolate these three compounds as solids. Below is a list of reagents available in lab. You may use any of these given reagents (e.g., acids, bases) as needed in your separation scheme and you also have access to a solvent evaporator if a solvent must be evaporated, and a filtration apparatus to filter. Be specific in each reagent name and technique used in your n scheme will receive the most credit. 10% aqueous NaOH 5% aqueous NaHCO3 6 M HC 5% HCI Saturated sodium chloride Diethyl ether anhydrous Na2SO4 Anhydrous MgSO4 OH Mg(CI2 2-methylbenzoic acid naphthalene ium chloride magnes

Explanation / Answer

Dissolve the mixture of 2-methylbenzoic acid, naphthalene and MgCl2 in diethyl ether. MgCl2 is an ionic compound and will not dissolve in the non-polar diethyl ether; MgCl2 will separate out from the ether layer as a solid residue. Filter the mixture. The residue is MgCl2. The filtrate contains 2-methylbenzoic acid and naphthalene. Call this filtrate F1.

Wash the precipitate with 5% HCl. MgCl2 dissolves in HCl. Heat the solution to evaporate water as water vapor. More or less dried MgCl2 is obtained.

Add 10% aqueous NaOH to the filtrate F1. 2-methylbenzoic acid dissolves in NaOH forming the sodium salt. Separate by solvent extraction technique using diethyl ether. The aqueous layer contains 2-methylbenzoic acid (as the sodium salt) and the diethyl ether layer contains naphthalene.

Add 6M HCl to the NaOH layer. HCl will neutralize NaOH. Solid 2-methylbenzoic acid is obtained. Separate by filtration. Dry the residue by adding anhydrous MgSO4. Re-crystallize from water.

Evaporate diethyl ether to obtain solid naphthalene.

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