Preparations of Chlorine

This demonstration shows how chlorine can be synthesised using either potassium permanganate (KMnO4) (1:40) or manganese dioxide (MnO2) (3:11). These substances can both behave as oxidising agents, the former being the more powerful.
In each case, concentrated hydrochloric acid is added to the solid oxidising agent. In the case of the more reactive potassium permanganate, this reaction occurs without heating.
Manganese dioxide is a less powerful oxidising agent and will only react with concentrated hydrochloric acid when heated. This method was used by the Swedish chemist Carl Wilhelm Scheele in the original isolation of chlorine in 1774. It is worth noting that this reaction is predicted to be unfeasible using the data from standard electrode potentials. As you can see from this video, this prediction is not valid in conditions that are not standard: both heat and concentrated acid are involved.
In each case, the chlorine that is produced is bubbled through alkaline universal indicator. Chlorine reacts with the hydroxide ion in the alkali to produce the chloride ion (Cl-) and the chlorate(I) ion (ClO-). This combination means that the universal indicator will initially tend from blue to green (due to the alkali reacting and being removed) before turning colourless (due to the bleaching effect of the ClO- ion).
The predominant application of manganese dioxide (MnO2) is as a component of batteries. Potassium permanganate (KMnO4) has several uses. For example, it can be thermally decomposed (240 0C) to make a convenient source of oxygen in the lab. The reaction between potassium permanganate and concentrated sulfuric acid should never be attempted: a green liquid called manganese(vii) oxide is produced. This is explosive and detonates at 50 0C.