In the classic Doctor's sweetening test used for detecting/removing mercaptans in light petroleum products, the Doctor\'s solution is a solution of sodium plumbite prepared in which medium?

Introduction:
The Doctor's test (and related sweetening process) targets mercaptans in gasoline and kerosene-range streams. Correct identification of the Doctor's solution composition is important for lab testing and historical sweetening methods.

Given Data / Assumptions:

• Doctor's solution contains sodium plumbite (Na2PbO2).
• Used with elemental sulfur in the classic sweetening step.
• We seek the solvent/medium in which sodium plumbite is prepared.

Concept / Approach:
Sodium plumbite is prepared in a strongly alkaline medium. The conventional Doctor's solution is sodium plumbite dissolved in aqueous caustic soda (NaOH). Under alkaline conditions, mercaptans can be converted and the mixture facilitates the qualitative “Doctor test.”

Step-by-Step Solution:
1) Recall that plumbites are stabilized in caustic (alkaline) solution.2) Associate the Doctor's solution with NaOH-based preparation.3) Choose the aqueous caustic soda option.

Verification / Alternative check:
Textbook descriptions and ASTM-style lab write-ups specify sodium plumbite in caustic soda solution for the Doctor test; alcohol or neutral water are not standard for this preparation.

Why Other Options Are Wrong:
Alcohol/glycerol: Not the conventional medium for Doctor's solution.Neutral water: Insufficient alkalinity for stable plumbite formation.Soda ash: Weaker base; not the standard practice.

Common Pitfalls:
Confusing the Doctor test with other sweetening or extraction steps that may use different reagents or solvents; the defining feature is sodium plumbite in caustic.

Final Answer:
Aqueous caustic soda (NaOH solution)