An unknown substance has the composition of 77.87% c, 11.76% h and 10.37% o. the compound has a molar mass of 154.25 g/mole. what is the molecular formula?

We need to first calculate the empirical formula. Empirical formula is the simplest ratio of whole numbers of components in a compound,

Mass percentages have been given. We need to then calculate for 100 g of the compound

C H O

mass 77.87 g 11.76 g 10.37 g

number of moles 77.87/12 11.76/1 10.37/16

moles = 6.48 = 11.76 = 0.648

divide by least number of moles

6.48/0.648 11.76/0.648 0.648/0.648

= 10 = 18.1 = 1

rounded off

C - 10, H - 18 and O - 1

empirical formula - C ₁₀H₁₈O

mass of empirical unit = 12 x 10 + 1x 18 + 16 = 120 + 18 + 16 = 154

number of empirical units = molecular mass / mass of one empirical unit

= 154.25 / 154 = 1.00

Therefore molecular formula = C₁₀H₁₈O