To extract and purify caffeine from black tea leaves for analysis, lab technicians perform a series of sequential extraction steps. First, tea leaves are steeped in boiling water to release caffeine, tannins, and other water-soluble compounds. Sodium carbonate is then added to the hot water mixture. This alkaline substance converts the acidic tannins into water-soluble sodium salts, which will remain in the aqueous phase, while leaving the caffeine as a free base. Once the mixture cools to room temperature, it is transferred to a separating funnel, and dichloromethane () is introduced. The funnel is gently shaken, periodically venting the pressure, to allow caffeine to partition into the organic dichloromethane layer due to its higher solubility in organic solvents. Because dichloromethane is denser than water, the organic layer settles at the bottom of the funnel and is drained into a clean flask. Crucially, the remaining aqueous layer is extracted two more times with fresh dichloromethane to maximize recovery. The combined organic fractions are then dried by adding anhydrous sodium sulfate, which binds any residual water. After filtering out the drying agent, the dichloromethane is evaporated under a gentle stream of nitrogen, leaving behind crude caffeine crystals.
Based on the passage, what is the most likely consequence of omitting the addition of sodium carbonate to the tea mixture prior to the dichloromethane extraction?
- The acidic tannins would remain in a form that dissolves in dichloromethane, leading to contamination of the extracted caffeine.Answer
- BThe caffeine would react chemically with dichloromethane to form water-soluble compounds, preventing it from partitioning into the organic layer.
- CThe dichloromethane would fail to settle at the bottom of the separating funnel, remaining trapped in the upper aqueous layer.
- DThe water-soluble compounds would immediately precipitate out of the solution before the mixture has a chance to cool.