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

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.

Answer 2

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