Question

A compound is found to be 40.0% carbon, 6.7% hydrogen, and 53.5% oxygen. Its molecular mass is 60. g/mol. What is its molecular formula?

Answer 1

Carbon=10.0
Hydrogen=6.7
Oxygen=53.5
Next, divide by their atomic masses. The atomic masses of the elements are;
Carbon=12, Hydrogen=1, Oxygen=16
So that will be
Carbon=40/12=3.3
Hydrogen=6.7/1=6.7
Oxygen=53.5/16=3.3
Next, divide by the smallest number. The smallest number is 3.3
Carbon=3.3/3.3=1
Hydrogen=6.7/3.3=2
Oxygen=3.3/3.3=1
So the empirical formula will be
C₁H₂O₁ which is the same as CH₂O
To get the molecular formula;
(CH₂O)n=molecular mass
Now we need to find n
(CH₂O)n=60
Multiply the atomic masses of each by the subscript and add them all
C₁=12 x 1=12
H₂=1 x 2=2
O₁=1 x 16=16
(12+2+16)n=60
(30)n=60
Divide both sides by 30
therefore; n=60/30
n=2
Next, multiply CH₂O by 2
C=1 x 2=2
H₂=2 x 2=4
O=1 x 2=2
So you have the empirical formula to be C₂H₄O₂
Hope that helped. Have a nice day