Quick Gold

Concept: Chemical Reactions can occur slowly.

Materials: 2 stirring rods

Beaker A:
2g Sodium Arsenite

11 mL Glacial Acetic Acid

100 mL water

Beaker B: 20 g Sodium Thiosulfate

100 mL water

Demonstration:

Mix the contents in each beaker with a stirring rod, until everything dissolves.

When ready to demonstrate, pour beaker A into Beaker B.

Introduction: "Today we're going to make some gold with these two solutions. It's going be quick to watch and see. (Pour solutions together and stir - nothing happens instantly but keep stirring while pretending something is wrong. pick up bottle, read the label making sure you have the right chemical the solution should turn bright yellow.) Oh look! I did do it right!"

Explanation: The Chemical reaction was delayed for a reason. This is a slow reaction. The acetic acid and the sodium thiosulfate react to produce hydrogen sulfide. This reaction is a slow process. Then hydrogen sulfide reacts with the sodium arsenite to create a yellow mixture, which is arsenic sulfide.

H₂S + 2As⁺³ ions ---> As₂S₃ + 2 H⁺ ions
hydrogen sulfide + arsenic ions ---> arsenic sulfide(yellow precipitate) + hydrogen ions

Safety:

Handle the Sodium Arsenite with care, it can be a poisonous chemical if ingested.
Pour the Glacial Acetic Acid using a ventilated hood. Fumes of acetic acid are corrosive.

Waste: Dispose of the final solution in its proper waste container - consult the instructor. DO NOT POUR IN SINK. Arsenic sulfide must be saved for proper hazardous waste disposal.

Reference: Unknown