Vinegar contains carbon, hydrogen, and oxygen with percent masses of 40.01% C and 6.70% H. If the molar mass of vinegar is about 60 g/mol, what is its molecular formula?

Question

a. CH2O

b. C3H7O3

c. C2H4O2

d. C3H8O

e. C2H20O

Answer 1

Vinegar contains carbon (C), hydrogen (H), and oxygen (O). You know the mass percent of C and H, so you can figure out the mass percent of O.

100 = 40.01% C + 6.70% H + x% O

x = 53.29% O

Using the molar masses of C, H, and O, you can develop an equation for the total mass of vinegar with a carbon atoms, b hydrogen atoms, and c oxygen atoms.

12*a + 1*b + 16*c = 60

You also know that 40.01% of the total mass of 60 g/mol is made up of C.

0.4001 * 60 = 24 g/mol

Knowing that each C atom has a molecular mass of 12 g/mol, that means that the formula contains 2 C atoms. Applying the same concept to H and O will let you know that the formula contains 4 H atoms and 2 O atoms.