How many moles of molecules are in 35 g of octane, #C_8H_18#?
There are 0.307 moles of molecules in 35 g of octane.
You start by finding the molar mass of octane,
This is 114 grams, because there are eight moles of carbon atoms and eighteen moles of hydrogen atoms in each mole of octane molecules.
So, we total up 8 x 12 (for the carbon) and 18 x 1 (for the hydrogen).
Next, take the given mass, and divide by this molar mass:
That's it! This answer is the number of moles of octane molecules contained in the 35 grams of the compound.