Abstract: During the experiment “Preparation and Calibration of Sodium Thiosulfate Standard Solution”, a significant amount of yellowish precipitation was unintentionally formed during the titration process by a freshman, due to the use of undiluted sodium thiosulfate solution. After conducting independent investigations, the students successfully reproduced the observed phenomenon and controlled the system’s pH to approximately 5, thereby preparing a relatively stable sulfur colloid system. Through additional literature research, estimation, and analysis, the students inferred the composition of the precipitate and hypothesized a homogeneous nucleation process for the precipitation of sulfur. Finally, based on their comparison, they recommended using sulfur colloid as a substitute for the traditional Fe(OH)₃ colloid in experimental teaching and classroom demonstrations.

Key words: Sodium Thiosulfate, Sulfur precipitation, Sulfur colloid