In the reaction Mg + O2 = MgO, 500mg of magnesium oxide was formed. How much oxygen has reacted with magnesium?

2Mg + O2 = 2MgO.

500 mg of magnesium oxide is 0.5 g. Knowing that 2 * 40 g of magnesium oxide is formed from 32 g of oxygen, we find the mass of oxygen, when interacting with magnesium, 0.5 g of oxide is formed:

32 g – 2 * 40 g

x g – 0.5 g.

Hence x = 0.2 g. The amount of oxygen is calculated by the formula:

n = m / Mr = 0.2 / 32 = 0.006 mol.

Considering that 1 mole of oxygen occupies a volume equal to 22.4 liters, we determine the required volume:

V = 0.006 * 22.4 = 0.13 l.