You need to know how much 1-octene you are starting with. In my lab it was 120 microliters. Change it to liters by dividing by 1000 to make milliliters (mL). I then multiplied by .72 (the density; g/cm3), divided by 112.22 (molecular weight; g/mol).
(0.120 mL Octene) x (.72g/cm3) x (1 cm3/1 mL)x (1 mol /112.22 g) x (1 mole H2/1 mole octene).
. :)