Question

What could be the molecular formula for a compound that contains 39.33% C, 8.269% H, and 52.40% O?

a) C4H2O
b) CHO
c) C3H6O
d) C2H5O2

Answer 1

d) C₂H₅O₂

Step-by-step explanation:

Molecular formula is a whole-number ratio of atoms presents in a molecule. The percentage given is in mass. Thus, we need to convert this percentage to moles using atomic mass of each atom and, in this way, we can solve for the ratio of atoms and molecular formula as follows:

C = 39.33g * (1mol / 12.01g) = 3.275mol

H = 8.269g * (1mol / 1.005g) = 8.228mol

O = 52.40g * (1mol / 16g) = 3.275mol

To obtain the ratio we must divide each amount of moles in the low number of moles (Moles of O or C):

C = 3.275mol / 3.275mol = 1

H = 8.229mol / 3.275mol = 2.5

O = 3.275mol / 3.275mol = 1

Multiplying this ratio in 2 (To obtain the whole-number ratio):

C = 1*2 = 2

H = 2.5*2 = 5

O = 1*2 = 2

The molecular formula is:

C₂H₅O₂

And right answer is:

d) C₂H₅O₂