If 38.5 grams of potassium react with excess oxygen gas, how many grams of potassium oxide can be produced? 4K + O2 yields 2K2O

46.40 g.

Explanation:

It is a stichiometric problem. The balanced equation of the reaction: 4K + O₂ → 2K₂O. It is clear that 4.0 moles of K reacts with 1.0 mole of oxygen produces 2.0 moles of K₂O. We should convert the mass of K (38.5 g) into moles using the relation:

n = mass / molar mass,

n = (38.5 g) / (39.098 g/mol) = 0.985 mole.

Using cross multiplication:

4.0 moles of K produces → 2.0 moles of K₂O, from the stichiometry.

0.985 mole of K produces →? moles of K₂O.

∴ The number of moles of K₂O produced = (0.985 mole) (2.0 mole) / (4.0 mole) = 0.4925 mole ≅ 0.5 mole.

Now, we can get the mass of K₂O:

∴ mass = n x molar mass = (0.5 mole) (94.2 g/mol) = 46.40 g.