As with all these problems, it is useful to assume that there is a 100*g100⋅g mass of compound, and divide each elemental mass thru by the ATOMIC mass of each component.
And so..........
"moles of carbon"-=(92.5*g)/(12.011*g*mol^-1)=7.70*molmoles of carbon≡92.5⋅g12.011⋅g⋅mol−1=7.70⋅mol
"moles of hydrogen"-=(7.50*g)/(1.00794*g*mol^-1)=7.50*molmoles of hydrogen≡7.50⋅g1.00794⋅g⋅mol−1=7.50⋅mol
And if we divide thru by the LOWEST molar quantity we gets.....and empirical formula of CHCH.
But the molecular formula is always a whole number of the empirical formula:
"molecular formula"="empirical formula"xxnmolecular formula=empirical formula×n
And so 78*g*mol^-1=nxx(12.011+1.00794)*g*mol^-178⋅g⋅mol−1=n×(12.011+1.00794)⋅g⋅mol−1; clearly, n=6n=6, and the "molecular formula"molecular formula is C_6H_6C6H6, which is what VERY common organic molecule?
