Question

Difficulty: MediumProcedural Steps

To extract limonene-rich essential oil from orange peels via steam distillation, laboratory technicians follow a precise sequence of steps to ensure maximum purity and yield. First, the outer flavedo of the orange peel is carefully grated, avoiding the bitter white albedo layer, which contains non-volatile compounds that can cloud the final distillate. The grated peel is immediately submerged in deionized water within a round-bottom flask to prevent the oxidation of volatile terpenes. Prior to heating the mixture, the flask is connected to a water-cooled West condenser, ensuring that the cooling water enters from the bottom port and exits through the top port to establish an efficient thermal gradient. The mixture is then heated to a gentle boil. As the steam carries the vaporized oil through the condenser, the distillate is collected in a receiving flask. Subsequently, sodium chloride is dissolved into the collected distillate; this increases the ionic strength of the aqueous phase, forcing the organic essential oil to separate from the water. Finally, the mixture is transferred to a separatory funnel where the top organic layer is drained and treated with anhydrous magnesium sulfate to absorb any remaining trace water.

Based on the passage, failing to dissolve sodium chloride in the collected distillate would most likely result in which of the following outcomes?

  1. the essential oil remaining poorly separated from the waterAnswer
  2. B
    the rapid oxidation of volatile terpenes in the flask
  3. C
    the accumulation of non-volatile compounds from the albedo layer
  4. D
    the loss of a proper thermal gradient within the condenser

Answer

the essential oil remaining poorly separated from the water
According to the passage, dissolving sodium chloride into the distillate increases the ionic strength of the aqueous phase, which forces the organic essential oil to separate from the water. If this step is omitted, the oil will not separate efficiently, leaving it poorly separated from the water.

Step-by-Step Solution

1
Locate the step in the passage involving sodium chloride.
The text states: 'Subsequently, sodium chloride is dissolved into the collected distillate; this increases the ionic strength of the aqueous phase, forcing the organic essential oil to separate from the water.'
Identifying the description of the target step reveals its intended outcome in the overall procedure.
2
Determine the consequence if this step is omitted.
Without the addition of sodium chloride, the ionic strength of the aqueous phase will not increase, meaning the organic essential oil will not be forced to separate from the water.
Omitting a procedural step prevents the physical or chemical change associated with that specific action.
3
Identify the option that matches this consequence.
The option stating 'the essential oil remaining poorly separated from the water' directly reflects the failure of layer separation.
Selecting the option corresponding to the lack of layer separation correctly answers the prompt.

Key Concept

Determining the purpose and sequence of specific stages in a scientific procedure.
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