preparation of oxygen gas in laboratory

Nowadays, oxygen gas used in secondary schools in Hong Kong is usually released from compressed oxygen tanks, but not prepared in laboratory.

When I was a secondary student in 1970s, oxygen is prepared in laboratory by heating KClO3 solid.
2KClO3(s) → 2KCl(s) + 3O2(g)
MnO2(s) can be added to act as a catalyst.

A easier way to prepared oxygen is the decomposition of hydrogen peroxide. When a small amount of MnO2(s) is added to a solution of hydrogen peroxide, oxygen is given off at a steady rate.
2H2O2(aq) → 2H2O(l) + O2(g)

The oxygen given off in either of the above two reactions can be collected over water.



2007-02-18 22:57:10 補充：
Refer to the following webpage :http://www.ucc.ie/academic/chem/dolchem/html/elem/elem008.htmlThere is a number of methods to prepare oxygen in laboratory. However, the two listed above are the commonest methods.