Question

A compound composed of 41.39% C, 3.47% H, and 55.14% O. The molar mass of the compound is 116.07 g/mol. What is the molecular formula of the compound?

Answer 1

we have mass of each elements as:
C: 41.39 g
H: 3.47 g
O: 55.14 g


Divide by molar mass to get number of moles of each:
C: 41.39/12.01 = 3.446295
H: 3.47/1.008 = 3.44246
O: 55.14/16.0 = 3.44625


Divide by smallest to get simplest whole number ratio:
C: 3.446295/3.44246 = 1
H: 3.44246/3.44246 = 1
O: 3.44625/3.44246 = 1

  
So empirical formula is:
CHO
Molar mass of CHO,
MM = 1*MM(C) + 1*MM(H) + 1*MM(O)
= 1*12.01 + 1*1.008 + 1*16.0
= 29.018 g/mol

Now we have:
Molar mass = 116.07 g/mol
Empirical formula mass = 29.018 g/mol
Multiplying factor = molar mass / empirical formula mass
= 116.07/29.018
= 4

Hence the molecular formula is : C4H4O4