When dissolving calcium carbonate in excess of hydrochloric acid, 2.8 L of gas was released. The mass of calcium carbonate is

Compose a reaction equation
CaCO3 + 2HCl = CaCl2 + CO2 + H2O
Calculate the amount of gas substance (CO2) = 2.8 / 22.4 = 0.125
Calculate the amount of substance of calcium carbonate (CaCO3) = 0.125 mol (equal to the amount of gas substance)
Calculate the mass of calcium carbonate m = 100 * 0.125 = 12.

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