Passing an electric current through a sample of water (h2o) can cause the water to decompose into hydrogen gas (h2) and oxygen gas (o2) according to the following equation. 2h2o right arrow. 2h2 + o2 the molar mass of h2o is 18. 02 g/mol. The molar mass of o2 is 32. 00 g/mol. What mass of h2o, in grams, must react to produce 50. 00 g of o2? 14. 08 28. 16 44. 40 56. 31.