45.5 mL of 0.0505 M NaOH is needed to titrate the HCl remaining in this 25.00-mL portion. What was the original mass of CaCO3 in the piece of chalk? A piece of chalk is placed in the 250. mL of 0.271 M HCl. All the CaCO3 reacts, releasing the carbon dioxide gas, and leaving a clear solution. 25.00 mL of the solution is pipette into another flask.