The marble containing 5% impurities was acted upon with an excess of 10% nitric acid solution, and 5.6 liters

The marble containing 5% impurities was acted upon with an excess of 10% nitric acid solution, and 5.6 liters (under normal conditions) of gas were released. Determine the mass of mineral used.

1) Let’s compose the reaction equation:
СaCO3 + 2HNO3 = Ca (NO3) 2 + CO2 ↑ + H2O
2) Let’s calculate the amount of substance CO2:
n (CO2) = V (CO2) / Vm = 5.6 / 22.4 = 0.25 mol.
3) Determine the mass of the mineral:
According to the reaction equation:
n (CaCO3) = n (CO2) = 0.25 mol
m (СaCO3) = n (СaCO3) ∙ M (СaCO3) = 0.25 ∙ 100 = 25 g.
ω (CaCO3) = 100 – ω (impurities) = 100-5 = 95%
m (mineral) = m (СaCO3) ∙ 100% / ω (СaCO3) = 25 ∙ 100/95 = 26.3 g.
Answer: 26.3 g