If you burn 33.1 g of hydrogen and produce 295 g of water, how much oxygen reacted?

                  262 g of O₂

                           First we will find out that either the given amount of Hydrogen gas can produce 295 g of H₂O or not. Therefore, the Balanced Chemical Equation is as,

                                                2 H₂  +  O₂    →    2 H₂O

According to equation,

                         4.04 g (2 mol) H₂ forms  =  36.04 g (2 mol) H₂O

So,

                                 33.1 g H₂ will produce  = X g of H₂O

Solving for X,

                       X =  (33.1 g × 36.04 g) ÷ 4.04 g

                       X  =  295 g of H₂O

Hence it is proved that given mass of H₂ can produce 295 g of H₂O.

The amount of oxygen reacted is calculated as,

According to equation,

                         4.04 g (2 mol) H₂ reacts with  =  32 g (1 mol) O₂

So,

                              33.1 g H₂ will react with  = X g of O₂

Solving for X,

                       X =  (33.1 g × 32 g) ÷ 4.04 g

                       X  =  262 g of O₂