Answer:
B.) 36.0 grams
Explanation:
To find the mass of water, you need to (1) convert grams Hâ‚‚ to moles (using the molar mass), then (2) convert moles Hâ‚‚ to moles Hâ‚‚O (using mole-to-mole ratio from reaction coefficients), and then (3) convert moles Hâ‚‚O to grams (using the molar mass). It is important to arrange the conversions in a way that allows for the cancellation of units.
Molar Mass (Hâ‚‚): 2(1.008 g/mol)
Molar Mass (Hâ‚‚): 2.016 g/mol
Molar Mass (Hâ‚‚O): 2(1.008 g/mol) + 15.998 g/mol
Molar Mass (Hâ‚‚O): 18.014 g/mol
2 Hâ‚‚ + Oâ‚‚ -----> 2 Hâ‚‚O
^ Â Â Â Â Â Â Â Â Â Â Â Â ^
4.0 g H₂       1 mole       2 moles H₂O      18.014 g
---------------  x  ----------------  x  ------------------------  x  ---------------  = 36 g H₂O
             2.016 g       2 moles H₂        1 mole
