Question

Naphthalene, commonly found in mothballs , is commonly found in 93.7% carbon and 6.3% hydrogen. The molar mass of naphthalene is 128g/mol. Determine the empirical and molecular formulas for naphthalene

Answer 1

assume 1000 grams of the stuff.
937 grams of C,or 937/12 moles C=78 moles
63 grms of H, or 63moles of H.
normalizing, 78/63 moles of C for every mole of H
C: 1.24 H: 1 is the empirical formula, but we want to put it in whole numbers, so finding a multiple of 1.24 giving a whole number, 4 is a starting pint C5H4 is a starting point, it is the empirical formula.
but we have more information: mole mass of 128g/mole
mole mass of empirical C5H4 is (5*12+4)=64, so we know the molar mass is twice the empirical formula:
molecular formula: C10H8