Hydrogen may be used in the future to replace gasoline as a fuel. Most major automobile companies are developing vehicles that run on hydrogen. These cars have the potential to be less environmentally harmful than our current vehicles because their only emission is water vapor. One way to obtain hydrogen for fuel is to use an emission-free energy source such as wind power to form elemental hydrogen from water. What mass of hydrogen (in grams) is contained in 1.00 gallon of water?

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SORT You are given a volume of water and asked to find the mass of hydrogen it contains. You are also given the den- sity of water. STRATEGIZE The first part of the conceptual plan shows how to convert the units of volume from gallons to liters and then to mL. It also shows how to use the density to convert mL to g. The second part of the conceptual plan is the basic sequence: mass → moles → moles → mass. Convert between moles and mass using the appropriate molar masses, and convert from mol H₂O to mol H using the conversion factor derived from the molecular formula. GIVEN: 1.00 gal H₂O dH₂0 1.00 g/mL FIND: g H CONCEPTUAL PLAN gal H₂O g H₂O 3.785 L 1 gal 1 mol H₂O 18.02 g H₂O L H₂O mol H₂O RELATIONSHIPS USED 1 gal 1L 1000 mL 1L 2 mol H 1 mol H₂O mL H₂O mol H 1.00 g 1 mL 1.008 g H 1 mol H 3.785 L 1000 mL 1.00 g H₂O = 1 mL H₂O (density of H₂O) Molar mass H₂O = 2(1.008) + 16.00 = 18.02 g/mol 2 mol H: 1 mol H₂O 1.008 g H 1 mol H g H₂O g H