Question

Acid/Base Extraction

Liquid-liquid extraction is a technique that can be used to physically separate two substancesthat have varying solubility properties. Typically an aqueous solution can be extracted with anorganic solvent to isolate a compound or vice-versa. The specialized piece of glassware that isemployed for these types of separations is called a separatory funnel.In this experiment a mixture of benzoic acid and naphthalene will be purified using liquid-liquidextraction, more specifically an acid-base extraction. Since both compounds are soluble inethyl acetate (an organic solvent), and benzoic acid is reactive toward aqueous bases, we canextract the benzoic acid out of the organic solvent into the aqueous solvent and physicallyseparate them. Neutralization of the aqueous solution will yield the purified benzoic acidproduct that can be characterized using melting point determination.

Benzoic acid and Naphthalene

Experimental Obtain a separatory funnel with stopper from the stockroom. Add 20 mL of ethyl acetate to theseparatory funnel followed by 2 g of the organic compound mixture. Swirl the contents of theseparatory funnel to dissolve the solids. If any residual compound mixture is stuck to the neck(the ground glass joint) of the separatory funnel wash it down into the funnel using a fewmilliliters of ethyl acetate.To the separatory funnel add 20 mL of 5% NaOH solution. Insert the stopper into theseparatory funnel and invert. Be sure to place the stopper into the funnel correctly. The groundglass joints form a water tight seal so that the solutions cannot escape during extraction. Pointthe drain away from others and immediately vent the separatory funnel by opening thestopcock. After relieving the pressure, close the stopcock and shake the contents to ensureefficient mixing. Vent periodically to relieve built up pressure. Place the separatory funnel onthe ring stand, remove the stopper and allow the solvents to separate. Drain the aqueous layerinto a 125 mL Erlenmeyer flask, label as flask A and set aside. Be sure to drain only the lowerlayer. Leave a small amount of the lower layer behind if necessary. Repeat the process ofadding sodium hydroxide solution and extracting two additional times. Combine all of theaqueous extracts into the same flask.

Prepare an ice bath in a 400 mL beaker. Place flask A into the ice bath and allow it to cool for3 minutes. Add 6M HCl solution portionwise (a pipette at a time) until the solution is stronglyacidic (pH<1). Test the pH by removing a drop of the solution using a glass stirring rod andplacing it on the pH paper. A white precipitate should form during the acidification. Isolate thesolid using vacuum filtration with a Buchner funnel and a filter paper. Wash the solid withplenty of water to remove residual acid. Place the solid in an open, labeled Petri dish and allowto dry over the course of a week. After allowing the sample to dry completely, identify the solidusing melting point analysis and obtain the mass and record the data in the laboratorynotebook.

Provide reactions that describe the acid-base extraction and neutralization processes used in this experiment. Provide a statement of solubility of each starting material and product

Answer 1

The acid-base extraction process of naphthalene and benzoic acid can be summed up in the following equation sequences: 1. On addition of NaOH, the mixture having naphthalene and benzoic acid undergoes the following chemical reaction and the two layers are separated out i e. Ethereal layer and the aqueous layer. COOH COO NaOH NaH,o Aqueous Layer contained in Flask A NaoH No Reaction The ethereal layer has naphthalene itself which is unreacted. 2. On addition of HCl to the flask A, the following reaction takes place and benzoic acid is isolated. Coo COOH HCI CI The benzoic acid is hence separated on the addition of HC1 to the aqueous layer and the ethereal layer gives us the naphthalene.

Solubility explaination:

On addition of sodium hydroxide, the benzoic acid is soluble in it and the reaction 1 occurs.

Napthalene gets separated in this way.

Answer 2

a statement of solubility of each starting material and product

first benzoic acid is soluble in ethyl acetate but naphthalene is insoluble so benzoic acid gets separated by filtration .

Then again NaOH is added to get sodium benzoate which is insoluble and can be collected in ppt form