An experiment found the empirical formula of C₄H₄O. More experimentation shows that the molar mass of this compound is 136 g/mol. What is the compounds molecular formula?

Answer 1

In equation form: M_MF/M_EF = n where n is the multiplier of the subscripts in the empirical formula in order to get the empirical formula.

Answer 2

The empirical formula for a chemical is an expression of the ratio of atoms in a molecule. A chemical with an empirical formula of C₄H₄O, for example, might have a molecular formula of C₈H₈O₂ OR C₄H₄O, because C₄H₄O is the smallest fraction of C₈H₈O₂!

Since the empirical formula only tells us the ratios of atoms, we need to know the molecular weight of the substance to figure out which chemical we're dealing with!

To do that, we will first look up the atomic weight of each component element.

C: 12

H: 1

O: 15.99 (for our purposes saying 16 probably works)

Since we know the ratio of atoms, we will merely figure out the molecular weight of the empirical formula, then multiply it by 2, 3, 4 etc until we find a molecular weight that matches 136 g/mol!

So

C₄= 12 x 4 = 48

H₄= 1 x 4 = 4

O = 16

48+4+16= 68

68 doesn't equal 136 so we go one more multiple down the line!

68x2 = 136

There we go! We found the molecular weight we were looking for by multiplying the empirical formula by 2!

This means that the molecular formula for the chemical with an empirical formula of C₄H₄O is C₈H₈O_2,

because it's just 2(C₄H₄O)

A) C₈H₈O₂