Solid substance changes its color from orange-red to pale yellow under heating.
name: Mercury (II) Iodide undergoes phase transition from alpha to beta crystalline form.
Mercury(II) Iodide and Thermochromism
Sodium iodide mercury chloride
Wear eye protection goggles and gloves. Mercury compounds are extremely toxic. Avoid body tissue contact with it.
Always follow general safety
recommendations. Please note that conducting chemistry
experiments you must comply with the relevant legal procedures in
HgCl2 + 2KI → HgI2 + 2KCl
HgI2 (red-orange alpha crystalline form) -[heating]→ HgI2 (pale yellow beta crystalline form)
- Fill the test tube with mercury (II) iodide. Mercury (II) iodide could be obtained by mixing mercury chloride solution with potassium iodide solution. They form the precipitate of mercury (II) iodide which could be separated from the solution by filtration.
- Put the test tube with mercury (II) iodide on a stand.
- Heat the test tube with a gas burner.
- The substance changes color from orange–red to pale yellow.
At 126 °C mercury (II) iodide undergoes phase transition between red-orange alpha and pale yellow beta crystalline forms. Such an ability of a substance to change its color with temperature change is called thermochromism.