When an excess of hydrochloric acid acts on a mixture of magnesium carbonate and magnesium oxide

When an excess of hydrochloric acid acts on a mixture of magnesium carbonate and magnesium oxide (the mass of the mixture is 10 g), 2.24 liters of gas will be released. Calculate the mass fraction of magnesium carbonate in the initial mixture.

Given:
m (mixture) = 10 g
V (gas) = 2.24 l
Find: w (MgCO3) -?
Decision.
Let us write down the equations of the mentioned reactions.
MgCO3 + 2HCl -> MgCl2 + H2O + CO2 (1)
MgO + 2HCl -> MgCl2 + H2O (2)
n (CO2) = V / Vm = 2.24 / 22.4 mol = 0.1 mol.
According to the reaction equation 1, n (MgCO3) = 0.1 mol.
m (MgCO3) = Mn = 0.1 × 84 = 8.4 g.
w (MgCO3) = m (MgCO3) / m (mixture) × 100% = 8.4 / 10 × 100% = 84%.
Answer: 84%