How many grams of 30% nitric acid is required to react with 250 g of limestone containing 20%

How many grams of 30% nitric acid is required to react with 250 g of limestone containing 20% impurities? How much carbon dioxide is generated?

Given:
w% (HNO3) = 30%
m (known) = 250 g.
w% (approx.) = 20%
m (solution) = 20%
V (CO2) -?

Decision:
1) 2HNO3 + CaCO3 = Ca (NO3) 2 + CO2 + H2O
2) m (CaCO3) = 250 * (100-20) / 100 = 200 g.
3) n (CaCO3) = 200/100 = 2 mol
4) 2n (CaCO3) = n (HNO3) = 2 * 2 = 4 mol
5) m (HNO3) = 4 * 63 = 252 g.
6) m (p-pa) = 252 * 100/30 = 840 g.
7) n (CO2) = n (CaCO3) = 2 mol
8) V (CO2) = 2 * 22.4 = 44.8 l.

Answer: 840 g, 44.8 liters.