many cola soft drinks contain caffeine and benzoic acid (pKa 4.2), explain how you would isolate separately pure caffeine and benzoic acid from an aqueous solution containing both compounds

To isolate pure caffeine and benzoic acid from an aqueous solution containing both compounds, you can follow the process of extraction and separation. Here's a step-by-step explanation:

1. Acidify the Solution: To start the process, add a strong acid, such as hydrochloric acid (HCl), to the aqueous solution containing caffeine and benzoic acid. This will convert the benzoic acid into its water-soluble salt form (benzoate ion), while the caffeine will remain unchanged.

2. Extraction with Organic Solvent: Now, add an organic solvent, such as dichloromethane or ethyl acetate, to the acidified solution. Both caffeine and benzoate are more soluble in the organic solvent than in water, so they will partition into the organic phase.

3. Separate the Organic Phase: After shaking the mixture, allow the mixture to settle. The organic phase containing the extracted compounds will separate from the aqueous phase (containing impurities and remaining water-soluble compounds) due to different densities.

4. Transfer Organic Phase: Carefully separate the organic phase from the aqueous phase by either using a separating funnel or by decantation. Transfer the organic solvent containing the extracted compounds to a clean container.

5. Recover Benzoic Acid: To recover benzoic acid, the benzoate ion needs to be converted back to its original form. This can be done by adding a strong acid, such as hydrochloric acid (HCl), to the organic phase. The benzoic acid will precipitate out of the organic solvent as a solid.

6. Collect the Benzoic Acid: Filter the solution to separate the solid benzoic acid from the remaining solvent. Rinse the solid with a small portion of cold water to remove any residual impurities. Finally, dry the benzoic acid to obtain the pure compound.

7. Recover Caffeine: To recover caffeine, the remaining organic solvent needs to be evaporated. This can be done by either using a rotary evaporator or by simply allowing the solvent to evaporate slowly, leaving behind the caffeine crystals.

8. Collect the Caffeine: Once the solvent has completely evaporated, collect the caffeine crystals and ensure they are completely dry. This will yield the pure caffeine.

Following this process of extraction and separation, you should be able to isolate pure caffeine and benzoic acid from the initial solution containing both compounds.