Purpose: To separate and purify a solid carboxylic acid and a liquid neutral com
ID: 1031927 • Letter: P
Question
Purpose: To separate and purify a solid carboxylic acid and a liquid neutral compound dissolved in ether. Procedure: 1. Separation and purification of the carboxylic acid Transfer the ether solution to a separatory funnel. Wash the ether solution twice with 10 mL portions of 10% NaOH. (what is the purpose of this step?) Combine aqueous solutions and cool in ice bath. Add 6 M HCI while swirling to the cooled aqueous solution until it is acidic. (What is the purpose of this step, and what should you expect to see?) Make sure the solution remains acidic as sometimes the pH changes as the reaction progresses. Cool the acidified solution in the ice bath for another 5 -10 minutes. Collect the crude acid by vacuum filtration. Recrystallize the carboxylic acid using water as the solvent. Measure the melting point of this solid after is has been dried for a while.Explanation / Answer
From the aliquots of NaOH added in Part-1. it is taken that a fairly small quantity of acid-liquid mixture is present in the sample given, So considering a rough estimate of 25mL of ether layer, a reasonable amount of water to be used can vary from 25mL to 50mL as this is done purely to skive off any water-soluble impurities still stuck in the ether layer out of it thus increasing the organic layer's purity.
The reason for addition of saturated aqueous NaCl is to drive out of the organic layer any and all polar substances, especially salts which may linger by hydrophobic interactions with the ether or neutral compound thus contaminating the neutral liquid compound. Again, a reasonable quantity to use here would be anywhere between 10mL to 30mL.
The addition of sodium sulfate is done to dessicate the organic layer thus rendering it completely devoid of any residual water that may be in the organic layer and thus have with it all the other compounds so painstakingly driven into the aqueous layer. Sodium sulfate is used when anhydrous and upon combining with the water in the solvent will cease to be its free-flowing self and accumulate in clumps. Thus the reasonable amount of sodium sulfate to be added can only be judged then and there by continous addition followed by swirling till there is no clumping of the added sodium sulfate at which point the solvent considered totally water-free.
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