A sample of magnesium metal reacts with aqueous HCl to yield H2 gas: Mg1s2 + 2 HCl1aq2¡MgCl21aq2 + H21g2 The gas that forms is found to have a volume of 3.557 L at 25 °C and a pressure of 747 mm Hg. Assuming that the gas is saturated with water vapor at a partial pressure of 23.8 mm Hg, what is the partial pressure in millimeters of mercury of the H2? How many grams of magnesium metal were used in the reaction?