The synthesis and properties of this inorganic solid is described in Ellis et al. "Teaching General Chemisty: A Materials Science Companion." The material undergoes a phase transition from a red solid at room temperature to a dark brown solid above ~55 C. This is due to enhanced ion mobility in the high-temperature phase. When the synthesis is complete, the dry powder may be smeared onto heavy paper and then laminated with transparent tape or contact paper. This provides a means of handling the material without coming into direct contact with the mercury compound. The entire demonstration card may be heated with a heat gun or a hot plate to illustrate the phase change.
ABOVE LEFT: A Solid State Model of the low-temperature phase of copper mercury iodide.
ABOVE RIGHT: Smearing copper mercury iodide on heavy paper. Note the use of gloves and goggles.
BELOW LEFT: The demonstration card at room temperature.
BELOW RIGHT: The left side of the demostration card on a hot plate. Note the darkening of the powder.
Special thanks to Dr. David Shaw at the Madison Area Technical College for providing the pictures. We have evidence that this compound has been embedded deeply in plastic for use as thermochromic pasta and egg timers. A related compound, silver mercury iodide, is yellow at room temperature and orange at elevated temperatures.
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