The most way common method of preparing chlorine gas in the laboratory is by using manganese dioxide to oxidize hydrochloric acid, as shown by this equation:
`MnO_2 + 4 HCl -> Cl_2 + MnCl_2 + 2H_2O`
The manganese dioxide is heated with concentrated HCl, and the gas produced is bubbled through water to remove any HCl gas present.
Chlorine can also be prepared by dripping concentrated hydrochloric acid on potassium permanganate crystals:
`2 KMnO_4 + 16 HCl -> 2 MnCl_2 + 2 KCl + 8 H_2O + 5 Cl_2`
Chlorine is a greenish-yellow gas that isn't found free in nature because it's highly reactive. It's toxic to living things. It's found in many compounds, the most common being NaCl which is abundant in sea water.
Chlorine gas can be accidently produced by combining cleaning products that containing bleach with those containing ammonia. Because it's a heavy gas it displaces air near the ground and creates a health hazard.