What is the precipitant resulting from the following lab procedure?
Lab: Extraction of a Three Component Mixture
Introduction:
Understanding how a molecule will react based on its properties is the core of organic chemistry.
One of the easiest to understand “structure-activity” relations is acid/base chemistry. In addition, the
chemistry and thinking process in acid/base chemistry can be extended to be the basis for many of the
reactions that you will learn about in this class. This lab will take advantage of acid/base properties
in order to separate compounds using liquid/liquid extraction techniques. The following compounds
are present in the sample that you will be given and need to be separated into their pure components.
Benzoic Acid Ethyl-4-aminobenzoate 9-Fluorenone
Procedure:
In the main hood you will find the powdered mixture of the three compounds, Benzoic
Acid, Ethyl-4-Amino Benzoate, and 9-Fluorenone. Add this mixture to a clean separatory
(sep) funnel (be sure the stopcock and closed before you add anything to your funnel!)
and then add ~20ml of diethyl ether (often called simply „
ether‟.) Seal the funnel and
shake briefly to fully dissolve the compound mixture. Once dissolved, add ~20ml of 3M
HCl (pH <0), seal the sep funnel, invert it (keeping your fingers on the cap), briefly shake
the mixture, and then open the stopcock to vent pressure build up in the funnel. Note: Ether is
extremely volatile and will easily build up gaseous pressure from the heat of reaction. If
you do not vent your stopcock every few shakes, it may cause the lid to shoot off.
Continue to shake vigorously and vent periodically for ~30 seconds. After shaking, allow
the two immiscible layers to fully separate and then drain the bottom layer (water layer)
into a 50ml Erlenmeyer flask and label it “acid extract”. Note: If the lid is on your sep
funnel when you try to drain it, it may drain slowly or suck air bubbles up through the
stopcock. With the top layer (ether layer) still in the sep funnel, repeat the same process
using 3M NaOH (pH >14), again draining the bottom layer into a flask and label it base
extract. Once both acid and base extractions are finished, drain the remaining ether layer
into a third flask (pre-weigh this flask and write down the weight) labeled neutral extract.
Take your acid extract flask and slowly add to it
~8ml of 6M NaOH, then continue to add dropwise
additions of 6M NaOH until litmus paper shows a
shift from red to yellow/blue. Repeat the same with
your base extract using 6M HCl to neutralize it
until your litmus turns from blue to yellow/red.
Line a Hirsch funnel with a small filter paper (pre-
weigh your filter paper!) that just covers the holes
on the bottom of the funnel. Dampen your filter
paper with a few drops of water and, hooked to a
vacuum as shown in the picture, slowly poor your
acid extract into the funnel and filter the precipitant
from your neutralized acid (what does your flow
chart say this precipitant should be?) Remove the
filter paper (precipitant and all) and set it aside.
Repeat the process for your base extract on a new
piece of pre-weighed filter paper.
Vacuum filtration setup using a 25mL Erlenmeyer Flask
and Hirsch Funnel. Remember to clamp your funnel.
Once you have isolated your two compounds, carefully transfer them (little filter paper
and all) to two larger pieces of pre-weighed filter paper and place them in your drawer to
dry. You can place your neutral extract with the ether in it directly in your drawer.
Note: Due to ether's volatility, no boiling is necessary and it will have evaporated
overnight. Do not put samples in a closed vial. They must be exposed to the air to
dry . You must allow at least 24 hours before weighing your compounds in order to let them dry. If your compound appears wet, do not weigh it . Allow more drying time.
Once weighed, determine percent recovery. Put all solid wastes into the solids waste
container.
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