Question

Which of the following oxide is formed when potassium metal is burnt in excess of air:
(A) ${{K}_{2}}O$
(B) $KO$
(C) ${{K}_{2}}{{O}_{2}}$
(D) $K{{O}_{2}}$

Answer 1

The combustion of metals with an excess of air means that the metals react with oxygen gas. When an element or a compound reacts with oxygen, the product form is their corresponding oxides.

Complete step by step solution:
The reaction of potassium K with oxygen:
When molten potassium is treated with oxygen, potassium superoxide is formed ${{K}_{2}}O$. The salt contains potassium ions and oxide ions i.e. ${{K}^{+}}\text{ and }{{\text{O}}_{2}}^{-}$ions. Both the ions are bound together by ionic bonds. The reaction involved is:
$K+{{O}_{2}}\to K{{O}_{2}}$
Potassium superoxide is an inorganic compound that is yellow in colour. Potassium superoxide is paramagnetic in nature; it means that it has unpaired electrons. Potassium forms superoxide because the size of the compound is heightened by the size of the cation. And an interesting point is that potassium ion is the smallest ion which forms superoxide with ease.

Hence the correct answer is option (D) when potassium metal is burnt in excess of air, Potassium superoxide is formed.

Additional information:
Use of potassium superoxide:
-Potassium superoxide is used to supply oxygen and also to absorb carbon dioxide in the breathing apparatus.
-It is also used in canisters for firefighters.
-Potassium superoxide is also used in submarines because it is highly reactive.
-An ionic bond is the type of bond in which there is the electrostatic attraction between the ions with an opposite charge or between the atoms with a difference in their electronegativity.

Note: The oxides of different metals have oxygen in different oxidation states, the oxidation state of oxygen in potassium superoxide is $-\dfrac{1}{2}$. Whereas the oxidation state of oxygen in sodium peroxide and lithium oxide is -1 and -2.