A 19.9-mL volume of a hydrochloric acid solution reacts completely with a solid sample of magnesium carbonate, producing 183 mL of CO2 that is collected over water at 24.0 ? and 738 torr total pressure. What is the molarity of the hydrochloric acid solution? A sample of natural gas is 85.2% methane, CH4, and 14.8% ethane, C2H6, by mass. What is the density of the mixture at 18 ? and 771 mmHg?