Concentrated hydrochloric acid is 37.2% HCl by mass with a density of 1.19 g/mL. What mass of HCl is in 0.500 L?

1. Mass percentage needs the mass of the solution, but only a volume is given. 2. Convert the volume for unit cancellation: 0.500 L = 500 mL. 3. Use the density to get the solution mass: 500 mL x 1.19 g/mL = 595 g of solution. 4. Apply the mass percentage as a ratio: 595 g x 37.2 g HCl per 100 g solution. 5. That gives 221 g of HCl. 6. A rough check helps, since 500 g of a roughly 40 percent solution should hold about 200 g of HCl. 7. The value 595 g is the whole solution, not the acid inside it. 8. The value 186 g applies the percentage to 500 g and never uses the density at all. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.4 Other Units for Solution Concentrations_