Calculate the oxide formula knowing that the mass fraction of the element K in it is 83%.

Let’s implement the solution, write down the data on the condition of the problem:
According to the condition of the problem, the oxide formula is RxOy, W (K) = 83%, thus, the molecular weight is: M (RxOy) = M (K) + M (O) = 100 g / mol;
Based on this, the mass fraction of oxygen is: W (O) = 100 – 83 = 17%;
Let’s calculate the amount of potassium and oxygen moles by the formula:
M (K) = 39.1 g / mol;
M (O) = 16 g / mol;
Y (O) = m / M = 17/16 = 1;
Y (K) = m / M = 83 / 39.1 = 2.12 mol;
X: Y = K: O = 2: 1;
Molecular formula of the oxide: K2O (potassium oxide);
M (K2O) = 39.1 * 2 +16 = 94.2 g / mol;
Answer: the oxide formula is K2O