Question

Determine the empirical formula of a substance that has a molar mass of 62g/mole if a
sample of it has a mass of 7.170g (consisting of 2.776g of C, 0.690g of H, 3.700g 0) (BOX YOUR
ANSWER

Answer 1

For this problem, you do not need the molar mass. You would have needed it if they asked for the molecular formula.

2.776 g / 12.01 g (molar mass of carbon) = 0.2311 moles of C

0.690 g / 1.008 g (molar mass of hydrogen) = .6845 moles of H


3.700 g / 16 g (molar mass of oxygen) = 0.2312 moles of O

So you divide by the smallest number of moles. In this case, it would be 0.2311.

Carbon:

.2311 moles / .2311 = 1

Hydrogen:

.6845 moles / .2311 = 2.9619

Oxygen:

.2312 moles / .2311 = 1.004

So it would be CH3O.