Answer:
Explanation:
Octane is C8H18, carbon is C. Therefore, for every mol of C8H18 there will be 8 mols of carbon.
Convert 20 kg of octane to mols octane using molar mass of octane.
Molar Mass octane = (8*12.011)+(18*1.008)=114.23 g/mol, where 8 and 18 are the atoms in the molecule and 12.011 and 1.008 are the respective molar masses of carbon and hydrogen.
20kg C8H18 *1000g/kg * mol C8H18/114.23g C8H18 = 175.1 mols octane.
Now convert that number of mols to mols carbon:
175.1 mol C8H18 * (8 mol C/mol C8H18)=1400.8 mol C.
Now remember that a mol of any given atom=6.022*10^23 atoms.
So 1400.8 mol C=1400.8*(6.022*10^23) atoms C, which is equal to your final answer, 8.4*10^26 atoms. (round to 2 significant digits since the initial number given, 20, has 2 significant digits.)
The main thing you want to look for here is your conversion factors. Once you have those down it is simple algebra from there, so be sure to practice those!