6. Collecting gas over water, Mixtures of Gases) A piece of lithium metal was added to a flask of water on a day when the atmospheric pressure was 757.5 Torr. the lithium reacted completely with the water to produce 250,0 mL of hydrogen gas, collected over the water at 23C, at which temperature the vapor pressure of water is 21.07 Torr. (a) What is the partial pressure of hydrogen in the collection flask? The partial pressure of hydrogen = Torr (b) What mass of lithium metal reacted? g of lithium metal reacted