What volume of 2.00 M HNO3 stock solution is required to prepare 250 mL of 0.400 M HNO3?

Core Concept

Dilution adds solvent only, so moles of solute are conserved and M1V1 = M2V2 applies. Solving for the stock volume gives V1 = (0.400 M x 250 mL) / 2.00 M = 50.0 mL. Measuring 50.0 mL of concentrated acid and diluting to a final volume of 250 mL supplies exactly the 0.100 mol needed. The answer is the stock volume withdrawn, never the final solution volume.