Question

What mass of water, in grams, would have to be decomposed to produce 12.0 L of molecular oxygen at STP?

Answer 1

Here is a solved example stoichiometry problem. Just follow the steps. Remember that L at STP can be converted to moles by

?L x (1 mole/22.4 l) = ?moles.
http://www.jiskha.com/science/chemistry/stoichiometry.html