Tums tablets contain CaCO3 that reacts with stomach acid as follows:

Question

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)

 Suppose the tablet was analyzed by adding 50.00 mL of 0.200 M HCl, which resulted in leftover
excess HCl. The excess HCl was then analyzed by titrating with 20.00 mL of 0.100 M
NaOH. Calculate the mass of CaCO3 neutralized in this process.

Answer 1

Use the CaCO3 equation you have and add this one for the titration.
NaOH + HCl ==> NaCl + H2O

mols HCl initially = M x L = 0.01
excess HCl = mols NaOH = 0.002
mols HCl used for the tablet = 0.008
0.008 mols HCl x (1 mol CaCO3/2 mols HCl) = 0.004 mols CaCO3
g CaCO3 = mols CaCO3 x molar mass CaCO3 = ?