The Aloha Chemical Sunset
Publication No. 13057
A simple chemical reaction produces a colloidal solution, resulting in a chemical “sunset.”
Hydrochloric acid solution, 1 M, HCl, 60 mL*
Sodium thiosulfate solution, 0.2 M, Na2S2O3, 100 mL*
Chemical sunset cutouts (printed palm tree and circular cutout to fit Petri dish)*
Petri dish or glass culture dish, 100 mm x 15 mm*
Tape of Hawaiian music (optional)
*Materials included in kit.
Hydrochloric acid solutions are highly toxic by ingestion or inhalation; severely corrosive to skin and eyes. The sulfur produced in this reaction has low toxicity and may be a skin irritant. Sulfur dioxide is an irritant to eyes and other tissues. Wear chemical-resistant gloves, splash goggles and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The resulting solution/mixture may be fil¬tered and thrown in the trash according to Flinn Suggested Disposal Method #26a. The filtrate solution should be diluted with water, then neutralized with sodium carbonate, and then flushed down the drain with excess water, according to Flinn Suggested Disposal Method #24b.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Obtaining, evaluation, and communicating information
Disciplinary Core IdeasMS-PS1.B: Chemical Reactions
MS-PS1.A: Structure and Properties of Matter
MS-PS4.A: Wave Properties
HS-PS1.A: Structure and Properties of Matter
HS-PS4.A: Wave Properties
Crosscutting ConceptsCause and effect
Structure and function
MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Answers to Questions
The thiosulfate ion decomposes in acid solution, producing colloidal sulfur according to the reaction
S2O32-(aq) + 2H+(aq) → S(s) + SO2(aq) + H2O(l)As the colloidal sulfur particles grow, the light from the overhead projector is scattered. As the concentration of colloidal sulfur and its particle size increases, the shorter wavelengths of light are scattered while the longer wavelengths pass through, producing a red color in the projected beam. Eventually, the concentration and particle size of the colloid becomes so great that no light can be transmitted through the solution.
Special thanks to David A. Katz, retired, Wilmington, DE, for bringing this demonstration to our attention.