Question

the molecular mass of organic compound is 78 and percentage composition of carbon is 92.4% and hydrogen 7.6% .Find it's molecular formula .
plzz fast it's urgent​

Answer 1

we need to fill in the blanks with moles and reduce to smallest whole number ratio

C___ H___

change % to g and divide by molar mass

C 92.4/12.01 H 7.6/1.01

C 7.69 H 7.52

divide by smaller number

C 1.02 H 1.00

round to closest fraction (up to about 8th's)

C 1/1 H 1/1

so we have 

CH for empirical formula

molecular

(CH)* molar mass / empirical mass

(CH) * 78/13 = (CH)6 or C6H6 which is benzene

Answer 2

Molecular formula = Empirical formula x n

n = molecular mass / empirical formula mass

 

= 78 / (12+1)

= 6

Thus the molecular formula = Empirical formula x n

                  

= (CH) x 6 = C6H6