A compound has a molar mass of 118 grams/mol and the empirical formula C2H3O2 what is the molecular formula?

Question

of the compound?

Answer 1

All you have to do is count up the atomic masses of 2 C's, 3 H's and 2 O's and then find some multiple of the sum that will give you 118g. So here we go...

~24 g for 2 C's
~ 3 g for 3 H's
~ 32 g for 2 O's

Added up, that's 59 g. So you'll need about twice the amount of everything to get 118..

The molecular formula is thus C4 H6 O4

Answer 2

The molecular weight of the empirical formula is:

(2 x 12) + (3 x 1) + (2 x 16) = 59 grams/mole

that is, 2 atoms of carbon x the molecular weight of carbon 12 grams per mole, plus

3 atoms of hydrogen x the molecular weight of hydrogen 1 grams/mole, plus

2 atoms of oxygen x the molecular weight of oxygen 16 grams per mole.

The molecular weight of the compound is exactly twice that of the empirical formula:

2 x 59 = 118 grams/mole

So the number of each type of atom in the empirical formula is multiplied by two, to give the molecular formula:

C4H6O4

The molecular weight of C4H6O4 is (4x12) + (6 x 1)+ (4 x 16) = 48 + 6 + 64 = 118 grams/mole

Note: molar mass is the same as molecular weight.