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Liquid-Liquid Extraction Chem 31.1 Experiment 3TRANSCRIPT
Liquid-Liquid Extraction of Benzoic Acid
Liquid-Liquid Extraction of Benzoic Acid
Experiment 3 Chem 31.1
Presented by Gene Gansit and Marlon Valdez
Extraction
The act of extraction involves the withdrawing or pulling out of something from something else.
Important industrially and in everyday use
Oil Extraction, Brewing Tea and Coffee
Introduction
In chemistry, extraction is defined as the separation process by which a substance is taken from a matrix.
Liquid-Liquid Extraction
Relies on relative solubility of solute in two different solvents.
Immiscibility of the two solvents
Introduction
0.5g of benzoic acid was transferred to a 250mL beaker containing 100mL distilled water and was then stirred.
The resulting solution was then filtered using a pre-weighed filter paper. The filter paper was put in an oven at 80C until the paper was completely dry.
The weight of the undissolved benzoic acid left in the filter paper was determined.
The dissolved benzoic acid in the mixture was also determined.
An aliquot of 20mL from the filtrate was transferred to a separatory funnel.
Experimentation
10mL organic solvent of ether, hexane or acetone was added. The stopper was inserted securely and the funnel was inverted with the stop cock on top.
Excess pressure was relieved by shaking the funnel gently and opening the stop cock. This process was repeated until no excess pressure builds up within the funnel.
Separatory funnel was shaken vigorously for 1 minute and was let to sit upright in a rack. The stopper was removed on top of the funnel and the mixture was allowed to separate into two sharply defined layers.
The organic layer was drained and received with a pre-weighed 50mL beaker and was evaporated with a hot plate. Finally, the retained benzoic acid in the beaker was weighed.
Experimentation
Results
SolventAmount recovered% recoveryEther--Hexane0.02g50%Acetone--Liquid-Liquid extraction using hexane yielded 0.02g of recovered benzoic acid from the 0.0396g of dissolved benzoic acid per 20mL water, showing a 50% recovery.
Unfortunately, the lack of Ether and Acetone in the laboratory prevented the comparison of the relative efficiency of the three solvents in terms of extracting benzoic acid from water.
Cyclohexane was used in place of the missing solvents but the result did not yield benzoic acid, rather it showed a dark-brown colored substance during evaporation.
Results
Extraction takes advantage of the chemical properties of the solute and the two immiscible solvents
contact of the original solvent containing the solute and the extracting solvent that has the capability to dissolve the solute.
which solvents is the solute more soluble in (efficient extraction)
Key property = Polarity of Molecules
Discussion
Theoretical Basis
like dissolves like
Solute -SoluteSolvent - Solvent
Solute - Solvent
Discussion
SoluteSolvent interaction should be stronger than solutesolute and solvent-solvent
Strength is based on IMF
Ion-dipole > H-bond > Dipole-dipole > Induced-dipoles > LDF
Dissolution will not occur with substances with great differences of polarity
the supposed solute-solvent attraction would not be enough to break the solute-solute and solvent-solvent bonds.
Similar polarities of substances results to a more possible breaking of the initial bonds to form the product bonds (Therefore soluble)
Discussion
The extracting solvent should have an affinity with the solute (similar polarities)
Solute = Benzoic Acid
Slightly Polar
Sparingly soluble in water
The extracting solvents should be immiscible (different polarities)
Partial miscibility makes the solvents harder to separate and may add impurities with the recovered benzoic acid
Discussion
Discussion
Distribution of the solute between the two immiscible solvents can be expressed by the following equation:
The higher the KD, the more efficient the extracting solvent
Hexane and Cyclohexane
solubility of benzoic acid in cyclohexane and hexane is 0.100M and 0.075M, respectively.
low values are due to the non-polar characteristic of both cyclohexane and hexane; both hydrocarbons having no net difference of electronegativity in their component
LDF
Discussion
Acetone and Ether
theoretical solubility of benzoic acid in acetone and ether is 2.355M and 1.816M respectively.
High solubility is due to similar polarity with benzoic acid (dipole)
More soluble in Acetone because it is more polar due to the ketone group
Also means that Acetone is partially miscible with water because it is polar like water
NOTE: Ether is the most effective solvent because it exhibits high dissolution of Benzoic acid and immiscibility with water
Discussion
This experiment illustrated the idea of how organic compounds are extracted from a liquid matrix, and how a compound distributes itself in a mixture of two solvents. Given the limitations of the experiment, it is seen that hexane can be used as an extracting solvent, but without any other samples that yielded results, comparing the relative effectiveness of hexane as an extracting solvent is not possible. Although theoretically, ether is the most efficient of the three supposed solvents as it has the greater affinity to benzoic acid compared to hexane, and completely immiscible in water unlike acetone.
Conclusion
Since the experiment took a lot of time to finish, further experiments may also opt to attain more separatory funnels to be able to do two or all three extractions simultaneously, reducing the time required for each extraction. The experiment may also be modified by increasing or changing extracting solvents to show more relative and comparative data, although the solvent should not be reactive with benzoic acid or water. As ether and acetone were unavailable, cyclohexane was used as another solvent, and this proved to be fruitless as it was not able to recover any amount of benzoic acid, rather, a dark-brown colored substance. Also, the trials may be increased to produce more accurate results.
Recommendation
1.
Suppose 20mL of the saturated solution was treated with 10% NaOH, which solvent (hexane, acetone, ether) could extract most of the benzoic acid solution? Explain
C6H5OO- + Na+ C6H5COO-Na+
The presence of sodium in sodium hydroxide reacts with benzoic acid forming sodium benzoate, an organic salt that is polar and therefore becomes more soluble in water. This will decrease the overall percent recovery of all solvents since the KD value will decrease as the solubility of benzoic acid in water increases. The new KD value may be written as:
The most efficient extracting solvent would still be ether as benzoic acid is still more soluble in ether than in hexane, and is still immiscible to water and NAOH solution unlike acetone.
Problems and Questions
2.
What effect does partial miscibility of the two solvents have on the efficiency of the extraction?
Partial miscibility decreases the efficiency of liquid-liquid extraction since the two layers would be harder to separate. This in turn also means that the recovered substance may have impurities contained in the aqueous solution.
Problems and Questions
3.
Problems and Questions
SolventT, Solubility in 100g solvent at Ethyl methyl ketone8065Cyclohexane8182Benzene8051.8CCl4788.751.25Water10021.0A substance C 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 below are the solubility of X and Y in different solvents:
A.
Which is the best extracting solvent?
KD values of X and Y given the solvents are shown below.
Problems and Questions
SolventKDxKDyEthyl methyl ketone3.05.0Cyclohexane4.02.0Benzene2.51.8CCl44.41.25The best extracting solvent would be the solvent corresponding to a high KDx value and a low KDy value.
The best extracting solvent would be CCl4 having a KDx - KDy ratio of 4.4:1.25.
B.
Given a saturated aqueous solution of X and Y and using 100mL of solvent in (a), determine the percent recovery of X in a single extraction.
Problems and Questions
C.
Repeat (b) using 50mL of solvent in each two successive extractions. Determine the percent recovery and compare this with (b).
Problems and Questions
D.
What is the percent recovery of the minor component in a single extraction using 100mL solvent in (a)?
Problems and Questions
Alexandria, (n.d.) Extraction. Northern Virginia Community College
Fijal, Z., Loukeris, C.,Naghibzadeh, Z. & Walsdorf, J., (n.d.). Liquid-Liquid extraction. University of Illinois in Chicago
Liquid/Liquid extraction (n.d.). Penn State Department of Chemistry
Solubility of benzoic acid in organic solvents (October, 2014) Retrieved from http://lxsrv7.oru.edu/~alang/onsc/solubility/allsolvents.php?solute=benzoic%20acid
Solution and solubility (n.d.) Elmhurst College Retrieved from http://www.elmhurst.edu/~chm/vchembook/170Asolubility.html
References
The solubility of X in water = 2.0g
KDx=4.4=
100#
2
100#
x = 1.6g %=
1.6
2.0
100=80%
1
st
Extraction 2
nd
Extraction
KDx=4.4
=
50#
2
100#
x=1.4g
solute left = 2.01.4 = 0.6g
KDx=4.4
=
50#
0.6
100#
y=0.4g
Total Recovery = 1.4g + 0.4g = 1.8g
%=
1.8
2.0
100=90%
=
= 1.25=
100#
1.0
100# '(
z = 0.56g, %=
0.56
1.0
100=56%