Naphthalene,commonly found in mothballs,is 93.75% carbon and 6.25% hydrogen by mass.If naphthalene's molecular formula is twice its empirical formula,what would its molecular mass be?

Question

Quizplus · Accepted Answer

1) We assume that the empirical formula of naphthalene is CH (most simplified ratio of atoms)
2) We can calculate the molecular formula as C8H4 (twice the empirical formula)
3) The molar mass of CH is 12 + 1 = 13 g/mol
4) The molar mass of C8H4 is (8x12) + (4x1) = 96 g/mol
5) However, the question asks for the molecular mass in u (atomic mass units), so we divide by the Avogadro constant: 
96 g/mol ÷ 6.022 x 10^23/mol = 1.595 x 10^-21 u/molecule
6) The molecular mass, therefore, is approximately 128 u/molecule (rounded to the nearest whole number).

Naphthalene,commonly Found in Mothballs,is 93