The preparation reaction of chlorine is based on two very similar redox reactions in which there is oxidation of the Cl ion – by two energetic oxidants such as potassium permanganate and potassium dichromate in an acid solution. Two test tubes with distilled water are prepared; in one a spatula tip of potassium dichromate is added, and potassium permanganate. Then you add drops of hydrochloric acid sol. 37%. We note the change in colour from orange, which is typical of Cr6+ solutions to yellow-green of Cr3+ solutions; simultaneously chlorine, a gas with a pungent smell that, due to its density which is about 2.5 times greater than that of air, has formed which is not likely to leak from the test tube. Likewise hydrochloric acid sol. 37% is dropped into the second test tube; we observe the change in colour from deep purple, typical of Mn7+ ion solutions to almost colourless, typical of Mn2+ solutions. Similarly to the previous reaction chlorine has formed.
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