Occurrence, Preparation, Properties, and Uses

The naturally occurring isotopes of oxygen are listed in Table 11.1. Note that the percentage abundances vary somewhat with differing sources. The accuracy of the atomic mass of the element is somewhat limited by this variation, but nevertheless the atomic mass of oxygen served as the standard of comparison for other elements until 1961 when the International Union of Pure and Applied Chemistry (lUPAC) adopted carbon-12 as the new standard. 

Designation Symbol Mass, amu Percent abundance Range of % abundance 

Oxygen is the most abundant element in the Earth s crust and oceans. The atmosphere is now about 21% oxygen, but this has not always been the case. The original atmosphere of the newly formed Earth contained very little. AH oxygen in the present atmosphere is the result of biological activity—that is, through the action of photosynthesis [represented in Equation (11.1)] carried on by the members of the plant kingdom  

In the laboratory, oxygen used to be commonly produced by the decomposition of potassium chlorate, KCIO3, as shown in Equation (11.2)  

This reaction used to be commonly employed in first-year chemistry laboratory exercises, but reports of isolated explosions have forced its elimination from such situations. Great care should be used in preparing oxygen in this manner. A safer method is to oxidize a mild solution of hydrogen peroxide with potassium permanganate in acid solution, as shown in Equation (11.3)  

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