When heated in air, the alkali metals fo...

When heated in air, the alkali metals form various oxides. Mention the oxides formed by `Li,Na` and K.

Text Solution

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The reactivity of alkali metals towards oxygen increases on moving down the group with the increase in atomic size. Thus, Li forms only lithium oxide `(Li_(2)O)`. Sodium forms mainly sodium peroxide `Na_(2)O_(2)` along with a small amount of sodium oxide while potassium forms only potassium superoxide `(KO_(2))`.
`4Li+O_(2) overset(Delta)rarr 2Li_(2)O`
`6Na+2O_(2)overset(Delta)rarr underset("Sodium peroxide"("major"))(Na_(2)O_(2)) + underset("Monoxide"("minor"))(2Na_(2)O)`
`K+O_(2)overset(Delta)rarr underset("Potassium super oxides")(KO_(2))+underset("Peroxide")(K_(2)O_(2))+underset("Monoxide")(K_(2)(O))`
The superoxide `O_(2)^(-)` ion is stable only in presence of large cations such as K.Rb etc.

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When heated in excess of air, alkali metals form different types of oxides depending upon the nature of the metal. Which of the following alkali metals form surperoxides ?

All alkali metals except Li

All alkali metals except Li and Na

All alkali metals except Li, Na and K

All alkali metals except Fr

On heating lead nitrate forms oxides of nitrogen and lead. The oxides formed are :

`N_(2)O, PbO`

`NO_(2), PbO`

NO, PbO

`NO, PbO_(2)`

The metal which form amphoteric oxide is

iron

aluminium

sodium

calcium