Question

You react 2.43 grams of magnesium with oxygen from the air according to the following reaction. The final mass of the product, magnesium oxide, is 4.12 grams. How many grams of oxygen reacted? 2Mg + O2 → 2MgO

Answer 1

Answer:

The mass of oxygen that reacted is approximately 1.6 grams of oxygen

Explanation:

The given information are;

The mass of magnesium in the reaction = 2.43 grams

The final mass of the magnesium oxide = 4.12 grams

The chemical equation for the reaction is given as follows;

2Mg + O₂  →  2MgO

From which we see that two moles of magnesium, Mg, reacts with one mole of oxygen gas molecule, O₂, to produce two moles of magnesium oxide, MgO

The number of moles of magnesium present, $n_{Mg}$, is given as follows;

$n_{Mg} = \dfrac{Mass \ of \, magnesium}{Molar \ mass \ of \, magnesium} = \dfrac{2.43}{24.305} \approx 0.1 \ moles$

By the given chemical equation, 2 moles of magnesium reacts with one mole of O₂, therefore;

1 mole of magnesium will react with 1/2  moles of oxygen which is 0.5 moles of oxygen also;

0.1 mole of magnesium will react with 0.05 moles of oxygen

The mass of one mole of oxygen = The molar mass of oxygen = 32 g/mol

The mass of oxygen in the reaction = The number of moles of oxygen × The molar mass of oxygen

The mass of oxygen in the reaction = 0.05 × 32 = 1.6 grams

Also from the molar mass  of MgO which is 40.3044 g/mol, we have;

The mass fraction of oxygen = 16/40.3044 = 0.39698 ≈ 0.4

The mass of oxygen = 0.39698 × 4.12 = 1.636 g

Therefore, the mass of oxygen in the reaction is approximately 1.6 grams.