The acid unknown is benzoic acid. Would the mass of acid unknown recovered be to

Question

The acid unknown is benzoic acid.

Would the mass of acid unknown recovered be too low, too high, or, unchanged if the following errors were made during the experiment? Make sure you explain the reasons for your answers. a. You added too much concentrated hydrochloric acid to the "basic extract" beaker, i.e. litmus paper was dark red. b. You forgot to dry the ether solution containing the neutral component with anhydrous sodium sulfate before you evaporated the ether. c. You did not rinse the filter paper with ether, when you performed the gravity filtration to remove the sodium sulfate added to the ether layer.

Explanation / Answer

3. a) The basic extract is neutralized with concentrated HCl to yield the acid, which because of its water insolubility, precipitates out. It is critical to add an amount of HCl necessary to completely neutralize the base. A slight excess of acid is added to make sure that the solution is acidic. To obtain the maximum yield, the solution must be acidic.

If too much of concentrated HCl is added, there will not be enough water present to fully dissolve the resultant salt. The acid added should be strong enough to protonate but not so strong that it is likely to decompose the compound.

b) Ether is evaporated to yield the solid neutral compound. The ether solution containing the neutral compound contains some dissolved water. If the ether solution is evaporated without drying, the resulting solid neutral compound would be wet with water.

c) The filter paper should be rinsed with ether to ensure a complete transfer of neutral compound from the drying agent and filter paper.

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