A Separation and Purification Scheme

Topics: Solvent, Solubility, Ethanol Pages: 6 (1426 words) Published: September 30, 2008
Experiment 55 consists of devising a separation and purification scheme for a three component mixture. The overall objective is to isolate in pure form two of the three compounds. This was done using extraction, solubility, crystallization and vacuum filtration. The experiment was carried out two times, both of which were successful.

Background Information:
This experiment combined all the knowledge of the previous labs performed throughout the semester. An unknown mixture containing an organic acid or base and an organic neutral compound in nearly equal amounts needs to be separated to its separate components. An understanding of solubility, extraction, crystallization and vacuum filtration is necessary in order to successfully carry out the separation.

Solubility consists of a solute and a solvent. Elements that dissolve are “soluble” and elements that don’t dissolve are “insoluble”. If the components are two liquids, the terms “soluble” and “insoluble” are replaced with “miscible” and “immiscible”. The main guidelines in determining solubility are: 1. All hydrocarbons are nonpolar, 2. compounds containing the electronegative elements oxygen and nitrogen are polar, 3. halogens do not alter polarity, 4. adding carbons to a chain decreased polarity, 5. dipole-dipole interactions is the force of attraction between polar molecules (H-H bonds being the strongest), and 6. branching of compounds results in a greater solubility in water than the corresponding straight chain compound.

Extraction is the method of mixing a solution with a second solvent that is immiscible with the first solvent. The two liquids then form two distinct layers (phases) that can easily be separated from one another. After each extraction, tests can be done on each layer to identify the products.

Crystallization is the process of forming solid crystals from a uniform solution. A dissolved substance with a decreased solubility at a lower temperature will separate (crystallize) from the solution as it is slowly cooled. The crystals are separated from the solution using vacuum filtration. This involves use of a Hirsch funnel and a water vacuum system.

Materials needed to do this experiment:
Most of the glassware and laboratory equipment necessary to perform this lab was located in my lab drawer. Other equipment included: •Hot plate
Analytical balance
Disposable Pasteur pipets
Centrifuge machine
Melting point apparatus
The reagents and compounds needed were:
Unknown 2
Methylene chloride
1.0M NaOH
6.0M HCl
Anhydrous sodium sulfate
95% ethanol

Dissolve 0.5g of unknown mixture in the minimum amount of diethyl ether or methylene chloride oIf more than 4mL of solvent is required, the other solvent should be used •Once solvent is selected, the same solvent should be used throughout the procedure when an organic solvent is required Isolating Neutral Compound from mixture containing Acid/Base impurity •Add 0.150g of unknown to a centrifuge tube

Add 4mL ether to tube and cap it
Shake until all solid dissolves
Add 2mL 1.0M NaOH to tube and shake 30 seconds
Let layers separate
Remove bottom aqueous layer and place it in a test tube labeled “1st NaOH extract” •Add another 2mL 1M NaOH to centrifuge tube, shake 30s, let layers separate and remove bottom aqueous layer and put in a second test tube labeled “2nd NaOH extract” •While stirring, add 6M HCl dropwise to each of the two test tubes until acidic (test with pH paper) •To the ether layer in the centrifuge tube, add 2mL saturated aqueous sodium chloride •Shake 30s and let layers separate

Remove and discard aqueous layer
Transfer ether layer to clean, dry test tube
Dry ether layer over granular anhydrous sodium sulfate
Transfer dried ether solution to a preweighted test tube, leaving drying agent behind •Evaporate ether by heating tube in a hot water bath
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