Red Sunset

DESCRIPTION:
The reaction of sodium thiosulfate and hydrochloric acid produces colloidal sulfur which clouds the solution. As the sulfur concentration increases, shorter wavelengths are scattered and longer ones pass through, this causes an increase of reddish color to appear on the overhead.
Na2S2O3 + HCl → 2NaCl + SO2 + S + H2O

TOPICS COVERED:
wavelengths of light
precipitate reactions
color change
chemical change

MATERIALS NEEDED:
– cheesecloth with a hole in the center
– 400mL beaker
– 0.05M Na2S2O3
– 1M HCl w/ disposable pipet
– overhead

PROCEDURE:
1. Place the cheesecloth on the overhead, place the beaker over the hole
2. Add ~300mL of 0.05M Na2S2O3 to the beaker
3. Add 3 squirts of 1M HCl to the beaker

ADDITIONAL COMMENTS:
The reaction may take a minute or two to start changing. Depending on the cheesecloth, one may not be enough to block all light from the overhead, so 2 can be taped together and then a hole cut out.

SAFETY:
Safety goggles should be worn at all times.

REFERENCES:
Katz, D.A. “Red Sunset.” Chymist.com. Web. 21 Feb 2012.
http://www.chymist.com/red%20sunset.pdf

Handout