Question

The principal ingredient of certain commercial antacids is calcium carbonate. A student titrates an antacid tablet weighing 0.552 g with hydrochloric acid. If 28.5 mL of 0.250 M hydrochloric acid is required for complete reaction, what is the percentage of calcium carbonate in the antacid tablet? (Include a balanced molecular equation in your answer and show all your calculations)

Answer 1

Number of moles of HCl titrated , n = Molarity x volume in L

= 0.250 M x 28.5 mL x 10^-3 L/mL

= 7.125x10^-3 mol

CaCO3 + 2HCl ----> CaCl2 + H2CO3

From the balanced chemical equation,

2 moles of HCl requires 1 mole of CaCO3

7.125x10^-3 moles of HCl requires (7.125x10^-3 )/2 = 3.562x10^-3 moles of CaCO3

So mass of CaCO3 , m = number of moles x molar mass

= 3.562x10^-3 mol x 100(g/mol)

= 0.356 g

So percentage of CaCO3 = ( mass of CaCO3 / mass of sample ) x100

= ( 0.356 / 0.552) x100

= 64.5 %