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CHM 412
EXPERIMENT 1
EXTRACTION AND DRYING OF AN AQUEOUS SOLUTION
Objective
To learn the techniques of separating toluene from water (and other inorganic compounds) by
extraction and to learn the techniques of drying a dehydrated solution.
Pre lab assignment:
1) Write a paragraph what do you understand about polar solvents and give at least
three examples of polar solvents.
2) What is the meaning for the term immiscible solution?
3) Draw a diagram of separating funnel and a simple distillation apparatus set up.
Introduction
Removal of molecular solute from a liquid commonly practice from aqueous/water medium via
immiscible medium is known as solvent or liquid-liquid extraction. This technique commonly in
organic laboratory, where mixture of two immiscible liquids in a separating funnel, will be
shaken thoroughly after both the tap and stopper are closed. Any pressure built up from the
solvent vapor will be released from time to time by opening the tap.( refer to the diagram
provided in figure 1)
In this experiment the solvent is diethyl ether, ether family is well known having such as low
boiling point, which made the solvent easily distilled off and recycled. As one of the volatile
organic solvent the ether family is highly flammable.
Through observation both water/aqueous layer are immiscible, but water in some extend
dissolved/migrate in ether medium, (as air having water vapour /moist) can be seen by naked
eyes. Due to this fact the after the extraction the first stage of drying process involving the usage
of anhydrous substance such as magnesium sulfate or calcium chloride or any suitable drying
agent, then followed by distillation for further purification.
In solvent extraction procedure; to obtained higher percentage of recovery of product or
extraction it can be obtained through successive/multiple extractions, where equal of amount of
the solvent required will be used in multiple extractions.
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Opening the stopper to let out the gas
Figure:1
Chemicals
30ml of a mixture 50:50 ratio of water and toluene solution
40 ml of ether
Adequate amount of anhydrous magnesium sulfate
Apparatus
1 separating funnel, 150ml
1 retort stand
1 100 ml round bottom flask
1 condenser
1 still head
1 thermometer
1 filter paper
1 heating mantle
1 150 ml measuring cylinder
2 rubber hoses
1 adapter
1 pocket thermometer
1 filter funnel
1 150ml/250ml conical flask
Separating the bottom layer
Figure:2
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Procedure
1.
Add 30 ml mixture 50:50 ratio of water and toluene solution into a separating funnel.
2.
Add 20 ml of ether and shake vigorously. While shaking, open the stopcock occasionally
to reduce the pressure built within, stop this process when no more or very small amount
of pressure left. Leave the funnel to stand until the separation of the two layers stable or
clearly seen.
3.
Test a few drops of the bottom layer by mixing with distilled water in a beaker, after
identify which is organic and aqueous layers. Drain the ether layer containing toluene
(i.e. organic layer) into a clean and dry conical flask. Use the remaining solution
(aqueous layer) layer for a second extraction. Note: the aqueous layer will be returned
back to the separating funnel with a fresh batch of 20ml ether.
4.
Repeat steps 2 and 3 using another/fresh batch 20 ml ether.
5.
Dry the combined ether layers with adequate amount of anhydrous magnesium sulfate (or
anhydrous calcium chloride), this can be indicated by no more of the anhydrous solid
stuck at the bottom of the flask and a clear solution will be obtained. Filter out the drying
agent with gravitational filter funnel.
6.
Separate toluene from ether by distillation.
7.
Record the volume of toluene and ether obtained. Calculate the percentage of recovery
for both solvents.
8.
Draw the apparatus needed for extraction and distillation.
Questions
a) Anhydrous magnesium sulfate or anhydrous calcium chloride are examples of drying
agents which remove water reversibly. Why is it necessary to filter off these drying
agents before distillation?
b) Although most organic solvents are less dense than water, chloroform and
dichloromethane are not. Explain briefly how you would separate chloroform or
dichloromethane extract from an aqueous solution using a separating funnel.