Animated video: 37 principles of chemical reactions and their dangers – Red and Black

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Principle: This is a variant of the “iodine clock reaction”. The three colorless and transparent solutions used in the experiment contained, in order: 1) soluble starch and sodium metabisulfite; 2) mercury chloride; 3) potassium iodate. The reactions that occurred were as follows: 1) Sodium metabisulfite reacts with water to form sodium bisulfite: Na2S2O5 + H2O → 2 NaHSO3. 2) Sodium bisulfite reduces iodate ions to iodide ions: IO3- + 3HSO3- → I- + 3SO42- + 3H+. 3) As the concentration of iodide ions increases, the soluble mercury salts begin to form mercuric iodide precipitate (orange-red in color): Hg2+ + 2 I- → HgI2. 4) The remaining iodide ions react with iodate ions to form elemental iodine: IO3- + 5I- + 6H+ → 3I2 + 3H2O. 5) Elemental iodine combines with soluble starch to form blue-black complexes. Note: This modified version of the reaction was invented by two students from Princeton University; they added mercury salts to enable the reaction to produce both orange-red and black colors, and orange and black are the representative colors of Princeton University. This reaction is commonly referred to as the “Old Nassau Reaction,” with “Old Nassau” referring to Princeton University. Due to its color, it is also called the “Halloween reaction.” Recorder: ChemToddler'schannel Risk: High. Mercury chloride is highly toxic; there is a significant risk of harm from inhalation, skin contact, or accidental ingestion, so do not attempt to use it at home.