Separating Acids and Neutral Compounds by Solvent Extraction

Topics: Chemistry, Solubility, Solvent Pages: 5 (1456 words) Published: May 1, 2012
Separating Acids and Neutral Compounds by Solvent Extraction Introduction
The purpose of this experiment was to use solvent extraction techniques in order to separate a mixture consisting of a carboxylic acid (p-toulic acid), a phenol (p-tert-butylphenol), and a neutral compound (acetanilide). Extraction is the process of selectively dissolving one or more of the compounds of a mixture into an appropriate solvent, the solution that contains these dissolved compounds is called an extract (Manion, 2004).

Impurities that are present in the solution can be removed by extracting them from the original solvent into another solvent. This is done by mixing two immiscible (insoluble to one another) solvents (Manion, 2004). By mixing the solvents together rapidly the exchange of the desired product from one solvent will be transferred to the other and the impurities remain in the original solvent. The two solvent layers then completely separate from each other as they are immiscible. The process washing is the reverse process, it leaves the desired compound in the original solvent and the impurities are transferred to the second solvent (Manion, 2004).

The solvent selection generally is determined by polarity, on will be polar typically wathe while the other a non-polar solution (hydrocarbon). The solvent choices that are used will always separate as they are unlike molecules and will not be able to be dissolved into each other. The result is a layering effect of the solvents within the container they are held, the denser layer of the mixture will always appear at the bottom of the container. This phenomenon allows for quick identification of the layers within the experiment with a water drop test indicating which of the solvent take on the water is the aqueous layer.

If one of the compounds in the mixture can be converted into its ionic form it can be more easily extracted into an aqueous layer as it becomes soluble within the solvent (Manion, 2004). By use of acid-base reactions the ionic components that have been broken down due to the reaction become soluble with in the aqueous solutions.

The techniques also need to facilitate this experiment were the use of pH paper to
determine acidity; determine melting points of experimentally derived substances, separate solids from solution with vacuum filtration, and to speed evaporation by use of air. Materials and Methods

The extraction mixture was prepared by weighing out 0.25-.35 g of acetanilide, 0.4-0.6 g of p-toluic acid, and 0.4-0.6 g of p-tert-butylphenol. The exact masses weighed for the experiment were recorded in a lab notbook. Then in a 100-mL beaker 25 mL of tert-butyl methyl ether was added and the three solid compounds listed above were added and mix until dissolved. The solution was then poured into a 125-mL separatory funnel and place in a support ring attached to a stand.

The extraction of the p-toulic acid was carried out by the addition of 10 mL of 0.5M aqueous NaHCO3 being added to the separatory funnel. Then a glass stopper was placed into the funnel the funnel was inverted while keeping pressure on the stopper not allowing any of the mixture to spill out while the funnel was rocked back and forth in order to gently mix the two layers. The gas was released from the funnel periodically as the mixture was shaken until there was no longer any gas escaping from the open stopper in the funnel. The separatory funnel was then placed back on the supporting ring stand and the layers were allowed to again separate.

The identity of the two layers was then determined by introducing several drops water of just below the surface of the top layer of solution with a pasture pipette in the funnel. Observation of the aqueous layer’s change was noted. The glass stopper was removed from the funnel and the stopcock on the funnel was opened to drain the aqueous layer from the funnel into a clean and labeled 100-ml beaker. The...

Cited: Manion, J. 2004. University of Central Arkansas. Separating Acids and Neutral Compounds by Solvent Extraction. In: Signature Lab Series Chemistry Labs. (M. Stranz, editor) Cengage Learning. Mason, Ohio. 2008. Pp.45-63.
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