Engineering
Chemistry
Compounds of Alkali Metals
Oxides Peroxides Superoxides and Hydroxide
Question
The main oxides formed on combustion of Li, Na and K in excess of air are, respectively:
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Solution
Alkali metals form different oxides when burned in excess air due to stability trends. Lithium forms the normal oxide (Li2O) because its small size stabilizes it. Sodium forms the peroxide (Na2O2). Potassium, rubidium, and cesium form superoxides (like KO2) because their larger sizes stabilize the larger superoxide ion.
The stability order is: normal oxide < peroxide < superoxide as we go down the group.
Final answer: Li2O, Na2O2 and KO2