Question

if you burn 20.8g of hydrogen and produce 186g of water,ho much oxygen reacte

Answer 1

So if we find the moles of each: H2 (20.8/1 = 20.8mol) H2O (186/18 = 10.33) 

the equation is: 2H2 + O2 ===> 2H2O

its a 2:2 ratio between h2 and h20 so we use the limiting moles which is 10.33

to find mass: mass = moles x RFM 

Mass = 10.33 x  32 = 330.56 then since its a 2:1:2 divide by two 
mass = 165.28g