I need some help with this question. A piece of chalk (mainly calcium carbonate) is placed in 250 mL of 0.293 M HCl. All the CaCO3 reacts, realising CO2 gas, and leaving a clear solution. 50.00 mL of the solution is pipetted into another flask. 87.1 mL of 0.0567 M NaOH is required to titrate the HCl remaining in this 50.00 mL portion. What was the original mass of CaCo3 in the piece of chalk? So far i've found balanced chemical equations from the question... they are: 1. CaCO3 + 2HCl --> CaCl2 + CO2 + H2O 2. HCl + NaOH --> NaCl + H2O Where should i go from there, the info given is really overwhelming.