Potassium peroxides

Several peroxides have been described. The tetroxide, K₂O₄, or K₂O₂,O₂, is produced by burning the metal in air or oxygen, de Forcrand heats the potassium first in a current of nitrogen, then in air, and finally in pure oxygen at a temperature between 180° and 200° C. The product is a sulphur-yellow, very hygroscopic powder, its heat of formation from the elements being 137.74 Cal. It is decomposed by water, with evolution of oxygen and formation of potassium hydroxide and hydrogen peroxide:

K₂O₄ + 2H₂O = 2KOH + H₂O₂ + O₂.

With dilute sulphuric acid it yields hydrogen peroxide.

When the tetroxide is heated at 480° C. under a pressure of 1 mm. of mercury, it is converted into potassium trioxide, K₂O₃, a yellow, crystalline substance, from which dilute sulphuric acid generates hydrogen peroxide. Its heat of formation from the elements is 124.34 Cal.

At -50° C. oxygen reacts with a solution of potassium in liquid ammonia to form the tetroxide and trioxide, and also potassium dioxide, K₂O₂. The heat of formation of the dioxide from its elements is about 108.8 Cal.