##CaCO3 + 2HCl -> CaCl2 + H2O + CO2## If it takes 0.0456 mol ##HCl## to completely react with all the ##CaCO3## in a 2.50g eggshell sample, a.) What is the mass of ##CaCO3## in the eggshell sample? b.) % ##CaCO3## in the eggshell sample?

a.) The mass of CaCO₃ is 2.28 g. b.) The mass % of CaCO₃ is 91.3 %.

Part a.) is a problem.

You must make the following conversions:

moles of HCl → moles of CaCO₃ → mass of CaCO₃

The balanced equation is

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

Mass of CaCO₃ = 0.0456 mol HCl × ##(1"mol CaCO₃")/(2"mol HCl")× (100.1"g CaCO₃")/(1"mol CaCO₃")## = "2.2823" g CaCO₃ = 2.28 g CaCO₃ (3 significant figures)

Part b.) is a mass percent problem.

% by mass = ##"mass of component"/"total mass"## × 100 %

% of CaCO₃ = ##"mass of CaCO₃"/"mass of eggshell"## × 100 % = ##(2.2823"g")/(2.50"g")## × 100 % = 91.3 % by mass