======Chemical Sunset======


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**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
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**Alternative titles:** Colloidal Sulfur Sunset, Tyndall Effect
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====Summary====                   
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====Procedure====  
  -Prepare a cardboard or heavy paper cutout to cover the projector surface, with a circular hole the size of a crystallization dish. Optionally attach an acetate sheet with a scene drawn in permanent marker.
  -Place 375 mL of deionized water in the crystallization dish.
  -Dissolve 2.8 g of sodium thiosulfate in the water.
  -Place the dish on the projector cutout. Darken the room and turn on the projector. The solution should appear colorless, and the projected light appears white.
  -Add 25 mL of 1.0 M hydrochloric acid and briefly stir with a glass rod.
  -Observe the changes: the projected light shifts from white to yellow, orange, red, and finally black, while the solution viewed from the side changes from transparent to white due to scattered light.



====Links==== 
Chemical Sunset - David Moyer: 
{{youtube>kP2W1E_SIP8?}}\\

Aloha Chemical Sunset - FlinnScientific: 
{{youtube>l7y1GoCLeRs?}}\\

📄 Chemical sunset - University of Waterloo: [[https://uwaterloo.ca/chem13-news-magazine/february-2016/activities/sharing-chemistry-community-chemical-sunset]]\\



====Variations====
  *Draw different images on acetate sheets (e.g., haunted house, beach scene) to enhance the effect.  
  *Adjust concentration of chemicals, dish size, or temperature to change the reaction rate. 



====Safety Precautions====
  *Wear safety glasses and gloves.  
  *Handle hydrochloric acid with care; it is corrosive.  
  *Sodium thiosulfate is an irritant; avoid ingestion and contact.  
  *Perform in a well-ventilated area; sulfur dioxide gas may be released.  
  *Avoid high temperatures, as hydrogen sulfide can also be released.




====Questions to Consider====
  *Why does the color of the transmitted light change during the demonstration? (Because colloidal sulfur particles grow in size and scatter different wavelengths of light.)  
  *How is this demonstration similar to a real sunset? (Shorter wavelengths like blue are scattered first, leaving longer wavelengths like red to pass through, just as in atmospheric scattering.)  
  *What factors influence the rate of color change? (Concentration of reactants, path length of light, and particle growth rate.)  
  *How could you design an inquiry to synchronize the “sunset” with different pieces of music? (By adjusting chemical amounts, solution depth, or reaction conditions to control timing.)