Chlorine is one of the most reactive and toxic elements that exists, making it very eager to react with other elements and molecules. Because of its highly reactive nature, chlorine gas is VERY dangerous and can easily overwhelm even the most experienced of chemists. As a result, it is best to not attempt to isolate chlorine unless the utmost care is taken to ensure that none of it is inhaled by anyone or anything, since death is a likely result.
At room temperature, chlorine takes the form of a yellowish-green gas. Chlorine gas is diatomic so atoms pair up to form small molecules. It is best to keep it in a sealed reaction system so that the gas cannot escape. To absorb the excess chlorine, you can attach the reaction flask to a flask containing some lye dissolved in water.
There are several ways to produce chlorine using readily available chemicals. The first method is to combine hydrochloric acid with potassium manganate, manganese dioxide, or magnesium oxide. Both are oxidizing agents and cause the hydrochloric acid (HCl) to break down into water (H2O) and chlorine gas (Cl2). This is represented by:
2HCl -> H2O + Cl2
In this case, the oxygen comes from the air and the oxidizing agents will not react at all.
Another good way to create chlorine gas is to take some bleach and place some sodium bisulfate into it. Sodium bisulfate can be found in certain household chemicals, or it can be purchased from online chemical suppliers.