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Liquid-liquid Extraction of Benzoic Acid

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Mian Malubay

on 13 August 2013

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Transcript of Liquid-liquid Extraction of Benzoic Acid

Liquid-liquid Extraction of Benzoic Acid
Introduction
Extraction is the separation of a component from a mixture by means of a solvent. It is usually used in separation of organic compounds from aqueous solutions or suspensions.
Methodology
Results and Discussion
Conclusion
Liquid-liquid extraction
Liquid–liquid extraction also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent.
Equation in Liquid-liquid extraction
Setup
Objectives
To understand the theory and to develop the skills needed in liquid-liquid extraction.
To identify the characteristics of an ideal solvent in such a process.
To study the different types of solvents.
To determine the best possible solvent based on the outcomes of both solubility and miscibility tests.
To learn how to compute for the percent recovery [%rec] for each extraction.

Calculate % recovery of benzoic acid in the extracting solvent (ether)
Weigh 0.5 g of benzoic acid and transfer it to a 250mL beaker containing 100mL water. Stir for 15mins.
Filter the solution using pre-weighed filter paper and set aside filtrate for the following procedure.
Dry the filter paper containing benzoic acid residue in oven at 80 degrees C for 20 minutes. Determine weight of undissolved benzoic acid
Weigh benzoic acid that is retained in the beaker
Take an aliquot of 20mL from the filtrate and transfer it to a separatory funnel then add 10mL ether
Insert stopper, invert funnel and open stopcock. Close stopcock, shake funnel gently for a moment, and open again. Repeat
Close stopcock and
shake
vigorously for 1 min. Place the funnel upright in the ring support. Remove stopper and allow to separate in defined layers
Drain off organic layer using 50mL beaker as receiver. Evaporate organic solvent
Calculation and Analysis of Results
Results
Percent Recovery
Compounds used
What is the best extracting solvent among the three?
Solubility of Benzoic Acid in different solvents
0.5g
0.35g
0.06g per 20mL a total of 0.3 per 100mL
Benzoic acid
100mL Water
10mL ether
85.7%
Solvent
Water
Acetone
Hexane
Ether
Molarity
0.027
2.355
0.075
1.816
g/ml
0.003294
0.28731
0.00915
0.221552
Solubility of Organic Solvents in Water
Solvent
Ether
Hexane
Acetone
%w/w
6.89
0.001
100
Problems and Questions
Suppose 20mL of the saturated benzoic acid solution was treated with 10% NaOH, which solvent (hexane, acetone ether could extract the most of the benzoic acid from the aqueous solution? Explain
What effect does partial miscibility of the two solvents on the efficiency of extraction?
A substance X can be isolated from its plant source by solvent extraction. However a minor component Y has an appreciable solubility in the solvents that may be used. Given are the solubilities of X and Y in different solvents
Which is the best extracting solvent? Explain
Given a saturated solution of X and Y and using 100mL of solvent (best), determine the percent recovery of X in a single extraction
Repeat (b) using 50mL of solvent in each of the two successive extractions. Determine the percent recovery and compare this with (b).
What is the percent recovery of the minor component in a single extraction using 100mL of the solvent in (a)?
Solvent
Ethyl methyl ketone
Cyclohexane
Benzene
CCl4
Water
T, (degrees C)
80
81
80
78
100
X
6
8
5
8.75
2
Y
5
2
1.8
1.25
1
X
3
4
2.5
4.375
Y
2.5
2
1.8
1.25
Solvent
Ethyl methyl ketone
Cyclohexane
Benzene
CCl4
Kd of solvent to X and Y
High Kd in X and low Kd in Y
Therefore CCl4 is the best extracting solvent
X=1.63g
Multiple extraction method as in this problem increases the benzoic acid's percent recovery.
Criteria for Choosing Extracting Solvent
High Kd when extracting one solute; High Kd for important solute and Low Kd for other solute when extracting from a mixture
Immiscible with original solvent
Density difference
More volatile than solute

Recommendations
Laboratory equipments must be in proper conditioning
Avoid deviation from procedure if possible
Proper weighing of materials
Thorough drying of filter paper and etc.
Avoid contamination of solvents by water
Achieving higher Percent Recovery
Choose a solvent that fits the criteria
Do as much extractions possible
References
Laboratory Manual in Organic Chemistry (2010e)
http://lxsrv7.oru.edu/
http://courses.chem.psu.edu/
Full transcript