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Make an Air Sensitive Solution

In this video we make a chemical solution that changes color when exposed to air and reverses when sealed away from air. In a vial about 20 mL in volume. Add 200 mg of copper chloride, 10 mL of hydrochloric acid (20% or higher in concentration) and 2 g copper metal. Seal the vial and let it sit overnight. It helps to include a stir bar and stir the solution overnight. What's happening is the copper metal is reacting with the copper (II) chloride in solution to produce copper (I) chloride. This reaction is called comproportionation where the same substance in two different oxidation states react to form a single substance of intermediate oxidation. Eventually the solution will go clear as all the copper (II) ions are converted to colorless copper (I) chloride. To observe the air sensitive reaction, simply open the cap and let the solution sit on air. Oxygen in the air will react with the copper (I) ions to convert them to copper (II) ions which are green in hydrochloric acid.