Question

8. Draw a flow diagram for this experiment. Indicate which phase contains each of the compounds in the mixture.

10. Why is it essential to carefully separate the layers during an extraction? What would happen if the layers were not separated completely?

11. You are given an impure solid that contains 70% of the desired product. After extracting 15 g of the material, you recover 6 g of the pure compound. What is the correct recovery?

12. how extraction works

13. The chemical process tha occurs during the extraction process

14. What was the reagent that you extracted in each phase

Answer 1

10. It is essential to carefully separate the layers during an extraction because tert-butyl methyl ether & the unknowns are organic compounds are flammable & may be toxic and irritants.  Avoid contact with skin or eyes & inhalation. Flush with water in case of contact & notify instructor. Keep these compounds away from open flames. Wear goggles & gloves at all times.

12.

Extraction

The general formula for a carboxylic acid is

                                                                        

where R stands for any group of atoms attached to the functional group COOH. As with any Bronsted acid, a carboxylic acid reacts with hydroxide ion, OH^-, to produce the conjugate base of the acid and water

            

            Carboxylic acid                                 Carboxylate anion

            insoluble in water                                soluble in water but

            but soluble in                                       insoluble in organic

            organic liquids                                     liquids

As is indicated, this reaction also changes the solubility properties of the acid molecule. We will take advantage of these property changes in separating the acid from the mixture.

            The neutral component of the mixture may be any one of the hydrocarbons, alcohols, ketones, or nitriles listed in Table 3-1. Neutral compounds will not react with either an acid or a base. They are also water insoluble but very soluble in organic liquids.

The Separation of the Aqueous and Organic Layers

            We have now identified the solubility properties of the two components of the mixture which will allow us to separate them. We will use liquid-liquid extraction to take advantage of the differences in solubility of the components. The organic liquid or solvent will be tert-butyl methyl ether (TBME) and the polar aqueous layer will be 5% NaOH or water.

            Initially the mixture of the neutral organic and carboxylic acid unknowns will be dissolved in TBME forming an organic solution. Suppose that this organic solution is shaken with a dilute aqueous sodium hydroxide solution and then allowed to stand until the two layers separate. During the shaking process, the hydroxide ion

will react with only the carboxylic acid      component of the mixture to form the water soluble carboxylate anion (see Equation 1 again). This changes the solubility properties of the acid as already stated and results in most of it moving from the organic liquid layer to hydroxide ion-water layer. The carboxylate ion thus is the solute and is extracted into the aqueous (water) phase. The two phases are then separated into two fractions: The aqueous sodium hydroxide solution containing the carboxylate anion as its salt and the organic layer containing the neutral organic compound.

            The two phases will separate and form two separate layers based on differences in polarity and density. The organic layer is much less polar and has a much lower density compared to the diluted NaOH solution. Sometimes the difference in polarity and/or density of the two phases may not be great enough to effect a separation causing the formation of an emulsion. The separation can sometimes be improved by adding more NaOH solution or TBME solvent.

            It is important to note that single extractions do not necessarily yield complete separations, and that multiple extractions may be needed. In your work, you will extract the original organic solution two times with aqueous sodium hydroxide solution to remove the acid and water soluble impurities from the organic layer. The two aqueous extracts are then combined and set aside as the aqueous sodium hydroxide fraction. The organic solution is further extracted once with distilled water to remove any water soluble impurities. Once these extractions are complete, the organic solution should contain only the "neutral" compound and the organic acid unknown should be extracted into the NaOH solution.

13.

During the extraction process, the hydroxide ion will react with only the carboxylic acid      component of the mixture to form the water soluble carboxylate anion.