Question

how many litre of oxygen at STP is required to burn 60 gram C2H6

Answer 1

mass of 1 mole of c2h6  = 12+12+6= 30 gm
hence no. of moles in 60 gm c2h6 = 2 moles
2 c2h6 reacts with 7O2 to burn 
hence 2 mole of c2h6 will react with 7 moles of oxygen
volume 7 mole oxygen at stp = 7 * 22.4 ( molar volume) 
                                               = 156.8 litres