Organic: Sodium Hydroxide and Erlenmeyer Flask

ABSTRACT

OBJECTIVE
To learn the concept of separating organic compounds by utilizing the concept of acid/base chemistry in so that separation can be done.
INTRODUCTION
Using acid base chemistry in the separation of substances can be a quite useful technique in organic chemistry. A basic extraction can be carried out by applying a hot solvent such as water to a dry substance like coffee. This will allow for the extraction of caffeine and flavor from the coffee beans. Acid base chemistry can be useful in separating neutral, basic, and acidic organic substances by controlling the pH of the aqueous layer. In acid base extraction a solvent such as ether is mixed with an aqueous solution of a different pH. This will aid in ionizing the intended compound and separate it from the mixture. Once the molecule is ionized it will precipitate out of the ether solvent and dissolve into the aqueous layer. The aqueous layer can then be removed and the pure substance can be obtained through crystallization.

In this week's lab a mixture of carboxylic acid, phenol, and a neutral substance were separated from an ether solution. First, the carboxylic acid was ionized with a weak base and removed. A strong base was then applied to the mixture to allow the phenol to ionize and precipitate into the aqueous layer. This layer of aqueous solution was then extracted which left the neutral compound in the ether solvent. The three separated substances were then crystallized for melting point and identification.
PROCEDURE
Isolation a neutral compound from a mixture containing an acid impurity 1. 0.24grams of unknown sample and 0.12 grams benzoic acid was weighted and placed in a test tube. 2. 10ml of ether was added to the mixture and was shakes to dissolve completely the mixture. 3. The solution then transferred to 125 ml separatory funnel and 5ml of 1M NaOH was added, with the cap tight, the layers was mix by swirling and shaking for 30 seconds. Pressure was vent by titling the funnel and opening the stop cork. 4. It was shakes again after closed the stop cork. The mixture was leaved to stand to allow the layers to separate. The aqueous layer was drain into Erlenmeyer flask and was labeled as first extraction NaOH. 5. 5ml of the 1M NaOH solution was added to the ether layer in the funnel and the step 1-5 was repeated and labeled as second extraction NaOH. 6. The flask was taken to the hood and by using glass rod slowly stirring when 6M HCl was added into each Erlenmeyer flask until the solution was acidic by using blue litmus paper. 7. The drying procedure for an ether layer requires the additional step, which not include in the procedure for drying of methylene chloride layer. 8. 5 ml of saturated aqueous sodium chloride was added. Then the mixture was shake for 30 seconds and let the layer separate. The aqueous layer was removed and discarded. 9. The ether layer was poured from the top of the seperatory funnel into the Erlenmeyer flask. 10. The ether layer over granular anhydrous sodium sulfate was dried 11. The dried ether solution was transferred, dry Pasteur pipet to a dry, reweighted Erlenmeyer flask, leaving the drying agent behind. 12. The ether was evaporate by heating the flask in a warm water bath. When the solvent was evaporated, the flask was removed from the bath and dry the outside of the flasks. When the flask was cooled to room temperature, the amount of solid solute was weighted. 13. The melting point of the solid was obtained.

Result 1. The actual weight of benzoic acid 2. Weight of benzoic acid recovered 3. Observed melting point of benzoic acid 4. Percent recovery o benzoic acid 5. Actual weight of unknown sample 6. Weight of unknown sample recovered 7. Observed melting point of unknown sample

Questions

1. List four water-immiscible liquids other than ether that could be used to extract organic compounds from aqueous solution. 2. Why is it wrong to leave a bottle of anhydrous sodium sulphate or calcium chloride open? 3. Draw the structure of the product when benzoic acid reacts with sodium hydroxide. Why is the product of this reaction easily extracted into H2O, while the original benzoic acid is not so easily exacted into H2O? 4. Why does benzoic acid precipitate out when the aqueous layer acidified with HCl? 5. Develop a procedure for isolating a neutral compound from a mixture containing a basic impurity by drawing a flow chart.

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