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Topic: Solubility of Solid in NaOH and Diethyl Ether  (Read 31053 times)

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Offline nate

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Solubility of Solid in NaOH and Diethyl Ether
« on: September 20, 2005, 01:05:27 AM »
Could anyone be able to tell me how likely would it be that a solid (benzoic acid) dissolved in diethyl ether would choose to move to 1M NaOH if the two liquids were mixed in a test tube.

I believe that when mixed, the two liquids are immiscible and the NaOH is the bottom layer due to greater density.  Although, when evaporating the Diethyl Ether in a steam bath, the benzoic acid was left behind.

Are my findings correct, or will there be some interaction between the benzoic acid and NaOH when the two liquids are mixed.

Offline mike

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Re:Solubility of Solid in NaOH and Diethyl Ether
« Reply #1 on: September 20, 2005, 01:35:40 AM »
It is highly likely.

hint 1: acid + base -> salt + water

hint 2: organic compounds are generally soluble in organic solvent and insoluble in water.

hint 3: salts are generally soluble in water yet insoluble in organic solvents.

So yes your findings are correct, almost, the substance left behind is not benzoic acid but the sodium salt of benzoic acid, and yes there is an interaction between the benzoic acid and NaOH.

There is no science without fancy, and no art without facts.

Offline lemonoman

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Re:Solubility of Solid in NaOH and Diethyl Ether
« Reply #2 on: September 20, 2005, 01:38:08 AM »
I THINK I understand what you're asking...so here goes:

When you have benzoic acid in diethyl ether...it is exactly that...benzoic acid...i.e. C6CH5COOH.  This is soluble in ether.  Yes this molecule is polar to a small extent, but not enough to make it precipitate from the liquid.

When you add NaOH solution, and shake vigorously (to ensure a fair equilibrium), then the NaOH deprotonates the benzoic acid, and leaves you with a benzoate ion...this is C6H5COO-.  This negatively charge ions is VERY polar, and is virtually insoluble in the ether.  It is however VERy miscible in the aqueous NaOH solution.

This allows the separation of benzoic acid from the ether...and adding strong acid to the queous NaOH will reprotonate the benzoate ion, reforming benzoic acid (which is not very soluble in water, and so it precipitates out)

Offline nate

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Re:Solubility of Solid in NaOH and Diethyl Ether
« Reply #3 on: September 20, 2005, 10:38:17 AM »
That was a great help.  Thank you both so much. ;D ;D ;D

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