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The Aloha Chemical Sunset
Materials
1. Hydrochloric acid 1M
2. Sodium thiosulfate solution 0.2M
3. Petri dish
4. Tropical sunset cutout
5. Overhead projector
6. Paper
7. Scissors
8. Tape or cd of Hawaiian music (optional)
Procedures
1. Trace a circle the size of the petri dish on a piece of paper and cut out the circle to provide a "frame" for the chemical sunset. Place this frame on the overhead projector.
2. To obtain a copy of the tropical sunset picture, go to www.finnsci.com/aloha.asp. open the pdf, print the picture and cut out along all of the outside edges to obtain a silhouette.
3.Place the tropical sunset cutout inside its circular frame.
4. Place the petri dish on the overhead projector and center the dish on top of the cutout,
5. Turn on the overhead projector and focus the tropical sunset picture on a projector screen or a wall,
6. Measure 14 ml of 0.2 M sodium thiosulfate solution and pour it into the Preti dish.
7. Measure 8ml of 1M hydrochloric acis solution and pour it into the Petri dish. Stir themixture.
8. Observe the color of the projected light on the screen or wall.
Discussion
Sodium thriosulfate and hydrochloric acid produce elemental sulfur according to the following equation.
Na2S2O3 (aq) + 2HCl(aq) ---> S(aq) + SO2(aq) + H2O(aq) + 2NaCl?(aq)
The Sulfur precipitates rapidly from solution, however the solid particles are large and therefore scatter light that is passed through the mixture. (Called the Tyndall effect) The changing colors of the sunset are caused when different wave lengths of light are scattered to different degrees.
Questions
1. Define colloid.
2. What is the Tyndall effect?
3. Explain how they got the values of 14 ml of sodium thiosulfate and 8ml of hydrochloric acid. (Use Molarities and molar ratios)