# By treating 30 g of limestone with hydrochloric acid, 11 g of carbon dioxide were obtained.

**By treating 30 g of limestone with hydrochloric acid, 11 g of carbon dioxide were obtained. Calculate the mass fraction of calcium carbonate in natural limestone.**

The dissolution reaction of limestone in hydrochloric acid is described by the following chemical reaction equation:

CaCO3 + 2HCl = CaCl2 + CO2 + H2O;

When 1 mol of limestone is dissolved in acid, 1 mol of gaseous carbon dioxide is synthesized. This consumes 2 mol of hydrochloric acid.

Let’s calculate the available chemical amount of carbon dioxide.

M CO2 = 12 + 16 x 2 = 44 grams / mol;

N CO2 = 11/44 = 0.25 mol;

Let’s calculate the weight of the same amount of calcium carbonate.

M CaCO3 = 40 + 12 + 16 x 3 = 100 grams / mol;

m CaCO3 = 0.25 x 100 = 25 grams;

The content of calcium carbonate in limestone will be:

K = 25/30 = 0.833 = 83.3%;