Question

A sample of a compound contains 60.0 g C and 5.05 g H. Its molar mass is 78.12 g/mol. What is the compound’s molecular formula? CH C2H2 C6H6 C6H

Answer 1

A sample of a compound contains 60.0 g C and 5.05 g H.

divide by molar mass of C(12) and H(1) to get molar ratio

C: 60/12=5 and H: 5/1=5

so C:H=5:5=1:1

total molar mass=78

divide by 1C+1H to find the formula: 78/(12+1)=78/13=6

compound is C6H6

Answer 2

Step 1: Calculate Moles for each Element:

Mole of C  =  60.0 / 12  =  5

Mole of H  =  5.05 / 1.008  =  5.009

Step 2: Calculate Mole Ratio:
                                             Divide each mole value with least mole value.

                                 H     :      C

                     5.009/5       :     5/5

                                  1    :     1
So,
           Empirical Formula  =  C₁H₁ or CnHn      ------ (1)

Step 3: Calculate Molecular Formula:
By using formula,
                               n  =  Molecular Mass / Empirical Formula Mass

Molecular Mass  =  78.12 g/mol

Empirical Formula Mass  =  12 + 1  = 13          ∴ C = 12 & H = 1
So,
                               n  =  78.12 / 13 

                               n  =  6

Putting value of n in eq. 1,
  
                                                  C₆H₆
Result:
            The correct answer is C₆H₆.