### molecular formula from empirical formula

The molecular formula of a compound is a multiple of its empirical formula. The empirical formula is the simplest formula of a substance, written with the smallest integers. For example, the molecular formula of benzene C6H6is equivalent to the empirical formula, (CH)6. This means that the molecular weight is some multiple of the empirical formula weight. The empirical formula weight is obtained by summing the atomic weights from the empirical formula. For any kind of molecular compound, we can write:

 Molecular weight = n * empirical formula weight

where n is the number of empirical formula units in a compound. We can get the molecular formula by multiplying the subscripts of the empirical formula by whatever n is. We can calculate this from the equation:

 n = (molecular weight)/(empirical formula weight)

Once we determine the empirical formula of a compound, we can calculate is empirical formula weight. If we have an experimental determination of its molecular weight, we can calculate n and then its molecular formula.

### molecular formula example:

A hydrocarbon is 84.25% carbon and 15.75% hydrogen and has a molecular weight of 114. What is its molecular formula?

 C 84.25/12 = 7.021 7.021/7.021 = 1 x 4 = 4 H 15.75/1 = 15.75 15.75/7.021 = 2.25 x 4 = 9
 4 C = 48 9 H = 9 57

114 / 57 = 2