Aimof the experiment.
Thecore principle underlying the test is to try and apply the knowledgeon chemical processes used in separation of mixtures. The two methodsto be used in this analysis are Solvent extraction operation and theThin Layer Chromatography. Solvent extraction separates mixturesusing a solvent while Chromatography monitors separation andestimates the extent of purity of the resulting compounds.
Theoryof the Experiment.
Thechemistry behind this experiment is to use these two processes toseparate mixtures and to calculate the level of purity of theobtained compounds. Solvent extraction is used mostly in organicchemistry to separate compounds that are in a mixture. The methodbases its separation on the solubility of the components found in themixture. It mainly applies two types of extraction techniques thatare solid-liquid extraction and the liquid-liquid extraction. Theformer involves the separation of a mixture and obtaining a solidwhile the latter involves two liquids. The liquids have to beimmiscible and possess different densities the difference indensities makes one liquid to float and hence they can be separated.A good example is ether and water the two are immiscible.
Thereagents to be used in the solvent extraction analysis are Benzoicacid, Ethyl 4- Amino Benzoate and 9-Flourenone. They act as an acid,the base and the neutral compound respectively. All the reactants areinsoluble in water. That is to mean that they are to be dissolved ina non-polar solvent such as Ether (Et2O)
Dissolve the three reagents in Ether. That is the acid (Ar-COOH), the base (Ar-NH2) and the neutral compound (Ar-H).
The resulting solution is then reacted with HCL. This results in there being two layers. The upper layer is composed of the acid and the neutral compounds. They are still in the ether layer since ether is less dense compared to water. The lower layer is composed of the base and water.
The next test is to look for a thin layer chromatography for Ether.
The two are separated to obtain two solutions.
The solution containing an acid and the neutral compound is then reacted with NaOH. The neutral compound remains in the Ether and floats while the acidic compound and sodium ions are in the layer below in the solution.
The two are then separated again.
The three compounds have been isolated from each other. They are labeled clearly.
Each component has to be isolated. That is to try and recover the original forms of the compounds by eliminating other unnecessary elements.
Recoveryof the basic compound
Itwill involve the use of Sodium Hydroxide on the basic solution whichis composed of the basic ions and the chloride ions. It results in appt. The precipitate is filtered dried and weighed this willbe used in calculating the percentages of recovery.
Recoveryof the acidic compound
Theresulting precipitate is to be filtered, dried and measured. Theweight of this precipitate is to be used in the calculation ofpercentage recovery.
Recoveryof the neutral compound
Asopposed to the recovery procedure of the acid and the base, theneutral compound requires extended separation techniques. It willneed to be first dried by the use of Sodium Sulphate. After drying,it is then slowly evaporated to remove the ether this is afterchecking the thin line chromatography of the Ether layer. The mixtureis then cooled and weighed. The weight is used to calculate thepercentage recovery of this component.
Thethin layer chromatography is used to determine the level ofseparation of compounds. Ether is always used in this study since itis less dense compared to water. In the experiment, chloroform isused since it is denser than water.
Theprinciples behind Thin Line Chromatography.
Thereare mainly two principles on which the thin line chromatographyoperates. First is the stationary phase, and the second is the mobilephase. The mobile phase comes into play when chloroform is used inthe analysis. The stationary phase used is a solid in this experimentit is Silica gel.
Severalapparatus are required to be used in the chromatography experiment.
Plates that are 6cm by 2cm
Plates should be coated with silica gel. This indicates the beginning of the stationary phase. This is because the gel is polar, and it is a Lewis acid.
Solvent to be used which in this case is the chloroform is used for elution. It is the mobile phase.
Measure about 0.5 cm and mark that as the origin.
Sample is placed on the origin and then it is dipped into a beaker that contains the solvent (chloroform)
Solvent must be at a level that is below the origin
Observe as the sample separates and different compounds move at different levels to various points on the sheet.
Compoundthat have strong interaction with the silica gel move up the plate ata slow pace as compared to those with a weak interaction. That mainlyapplies to the acids. Those with aweak interaction with the gel moveup at a faster pace, and this are mostly the basic compounds. Themovement along the plate needs to be put under observation by use ofthe UV light. That enables for the marking of the different spotsclearly using a pencil. It is an observation that more polar solventsmove further up the plate.
Calculationof the Rf Values
Rf values are obtained by dividing the distance travelled by thesample from the distance by the distance travelled by solvent frontfrom the origin.
Rf= distance travelled by sample (from origin)
distance travelled by solvent front.
Issuesthat may arise with Thin Line Chromatography
The compound show as a streak rather than a spot.
The sample runs as a smear
The sample runs as a downward crescent.
The plate solvent front moves crookedly.
Numerous random spots areseen on the plate.
You observe a blur of blue spots on the plate.
No spots are seen on the plate.
Dataand computations from the experiment.
Ethyl 4- Amino Benzoate
Thehydrochloric acid is used to recover the acidic mixture while thesodium hydroxide is used to recover the basic compound. The sodiumsulphate is used to dry the neutral compound so that it can berecovered from the solution. Each and every reagent is reacted withthe mixture so as to obtain the respective compounds.
Massof the mixture: 160 mg
Themixture contains 35% of each compound
Recoveryof each compound
Originalmass: 30801 mg
Newmass: 30776 mg
Changein mass: 30801-30776= 25 mg
Recovery=recovered sample * 100
Weight of impure sample
Ethyl4- Amino Benzoate
Originalweight: 30817 mg
Newweight: 30726 mg
Changein mass: 91 mg
Originalmass: 16765 mg
Newweight: 16727 mg
Changein mass: 38 mg
(91+25+38)/160 = 96. 3%
Thisexperiment shows clearly that nearly all compounds were recovered.
Inthe process of performing this test, a lot was learnt in thelaboratory. Knowledge and expertise were gained on how to performexperiments that require attention to detail. The experiment alsocreated more understanding on how components can be separated and thedifferent types of separation methods available. The experiments ledto the understanding that two or more compounds that were formerlytogether can be separated to obtain the original compounds. It alsobrought out an aspect that the new compounds recovered would not bepure. The analysis also helped to identify errors that may haveoccurred in the lab leading to the less than 100% recovery ofcompounds.
The compounds recovered seem to be slightly impure. There are nothuge variations in the numbers, so this leads to one assuming thatthe compounds extracted are the compounds that were expected althoughthey are not entirely pure, this is the usual expectation. The errorin the experiment could have resulted from a few different sources.One step that could have led to the errors was during separation. Ithad proved hard to extract only one layer of any of the compounds.That means that the resulting solution, whether it be acidic orhydroxide, would yield slightly less acidic than expected. It waschallenging to be precise with the separation that translates to theassumption thatthere was going to be an error in the final weighteither way.
"Extractionin Theory and Practice (Part I)." Extraction in the Theoryand Practice (Part I). 30 Dec. 2013. Web. 27 Oct. 2014.<http://www.chem.ucla.edu/~bacher/Specialtopics/extraction.html>.
"ThinLayer Chromatography (TLC)." Thin Layer Chromatography (TLC).Web. 27 Oct. 2014.<http://orgchem.colorado.edu/Technique/Procedures/TLC/TLC.html>.
"Liquid-LiquidExtraction." – Chemwiki. Web. 27 Oct. 2014.