To find the Empirical Formula and Empirical Formula:
First note down the percentages of the elements in the given compound.
Here, as the compound is a hydrocarbon, we know it involves Carbon and Hydrogen bonded to each other.
Carbon's atomic mass = 12
Hydrogen's atomic mass = 1.008
The compound contains 92.3g of Carbon. It implies it has;
mass of hydrogen = 100 - 92.3 = 7.7g
To find the no.of gram atoms of an element we divide the percentage mass by atomic mass of the said element.
no. of gram atoms of Carbon = 92.3/12 = 7.6916 gram atoms of Carbon
Similarly for Hydrogen,
no. of gram atoms of hydrogen = 7.7/1.008 = 7.63 gram atoms of Hydrogen
Divide all the value of gram atoms by the smallest value among them.
Thus, to determine ratios:
7.69/7.63 = 1.008
Carbon and Hydrogen are in 1:1 ratio.
The ratio between number of atoms gives us the empirical formula. Hence, empirical formula of given compound is: CH.
Molecular mass of a compound = n(empirical formula mass)
Empirical Formula mass = (12 * 1 ) + (1.008 * 1) = 13.008
Molecular mass is given in the question. Therefore, the equation becomes:
78 = n(13.008)
n = 78/13.008
n = 5.99 ≅ 6
Therefore, the molecular formula of the given hydrocarbon is: C₆ H₆
