liquid-liquid extraction

Topics: Chemistry, Benzoic acid, Water Pages: 5 (588 words) Published: February 18, 2015


Caroline Crites
Mr. Seacrist
Spring 2015
Experiment 4
Liquid – liquid Extraction
Partners: Ashley Byrd, John Puchelt

Abstract: The purpose of the experiment is to separate an acid and a neutral compound using their solubilities in liquid- liquid systems at different pH values. We recovered 0.75 grams of benzoic acid and 0.03 grams of triphenylmethane and found their melting points to be 114.6˚-116.8˚C and 80.3˚C-82.3˚C, respectively. We also found the retention factors for both the benzoic acid and the triphenylmethane to be 0.8 and 0.1, respectively. Experimental:

Physical Data
Sample mixture
MW
mp˚C
bp˚C
pH
Benzoic acid
122
121˚C-123˚C
249˚C
Benzoic Acid Reactions:

Reference: from lab manual page 35.
Procedure: Department of Physical Sciences.”Liquid-Liquid Extraction”. Laboratory Manual for CHM 211-002 (Organic Chemistry I). Lab Manual. Trident Technical College. Charleston.20102Print2pg 35-37. Observations: Both samples were clear and aromatic. There were also visible gas fumes. When HCl was added to the sodium benzoate, the solution got cloudy. Calculations:

Rf Value =
Triphenylmethane: = 0.76
Percent Recovery= X 100
Triphenylmethane: X100 = 56% Data:
Table 1. Distance recorded for each sample
Sample
Distance traveled by spot
Distance traveled by solvent
Retention Factor
Pure triphenylmethane
3.1cm
4cm
0.78
Recovered triphenylmethane
3.2cm
4cm
0.8
Pure benzoic acid
0.4cm
4cm
0.1
Recovered benzoic acid
0.4cm
4cm
0.1

Table 2. Melting points recorded for each sample
Sample
Melting Point (˚C)
Reference triphenylmethane(from lab manual)
94˚C
Original sample of triphenylmethane
71˚C-72˚C
Recovered sample of triphenylmethane
80.3˚C-82.3˚C
Reference benzoic acid (from lab manual)
121˚C-123˚C
Original sample of benzoic acid
121˚C-123˚C
Recovered sample of benzoic acid
114.6˚C-116.8˚C

Sample Plate
Table 3. Weight and percent recovery of the compounds
Sample Compound
Weight in grams
Percent Recovery
Triphenylmethane
0.75g
75%
Benzoic Acid
0.03g
3%

Conclusion:
Extraction is a process where compounds are transferred usually from one liquid phase to another. We used the chemically active liquid – liquid extraction method to convert a neutral species to a water soluble salt to allow the phase transfer and the separation. The compounds we separated were benzoic acid and triphenylmethane. Extraction is usually performed after a chemical reaction as part of the work up, where the product of the reaction is manipulated to isolate and purify it. Liquid-liquid extraction was used to separate the non polar triphenylmethane compound and the slightly polar benzoic acid compound. We started with 1 gram of each compound and dissolved it into 50mls of ether to separate it into an aqueous and an organic layer. We were only able to recover 75% of the triphenylmethane compound and 3% of the benzoic acid compound. The low percent recovery could be due to the sample compounds not being 100% pure, or that the reaction of the benzoic acid to the sodium benzoate did not go to completion. When we tested these in the Meltemp apparatus to determine a melting point, they were very similar to the reference melting points. The reference melting point of the original sample triphenylmethane was 71˚C-72˚C. Our recovered sample was 57˚C-59˚C. The original sample of the benzoic acid melting point was 121˚C-123˚C. Our recovered sample was 114.6˚C-116.8˚C. There was a small melting point depression which could have due to the fact that there was still some liquid left after it was dried,...
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