A. The empirical formula is the simplest ratio of components making up a compound.
In 100 g of the compound
C H O
mass 68.1 g 13.7 g 18.2 g
number of moles
68.1 g / 12 g/mol 13.7 g / 1 g/mol 18.2 g / 16 g/mol
= 5.68 mol = 13.7 mol 1.14 mol
divide by the least number of moles - which is 1.14 mol
5.68 / 1.14 = 5.0 13.7 / 1.14 = 12.0 1.14 / 1.14 = 1.0
the ratio of the components C : H : O is 5: 12 : 1
therefore empirical formula is C₅H₁₂O
B. Molecular formula is the actual ratio of the components making up the compound. We need to find the mass of the empirical formula / empirical unit and then find how many empirical units make up the molecular formula
mass of 1 empirical unit - C₅H₁₂O - 12 g/mol x 5 + 1 g/mol x 12 + 16 g/mol x 1
= 60 + 12 + 16 = 88 g
number of empirical units = molecular formula mass / mass of 1 empirical unit
= 176.34 g/mol / 88 g = 2.00 = 2
there are 2 empirical formulas in the molecular formula
therefore molecular formula = 2 x (C₅H₁₂O) = C₁₀H₂₄O₂ ,
therefore molecular formula is C₁₀H₂₄O₂
