Question

Find the total number of atoms in a sample of cocaine hydrochloride, c17h22clno4, of mass 23.0 mg .

Answer 1

From the periodic table:
mass of carbon = 12 grams
mass of hydrogen = 1 gram
mass of nitrogen = 14 grams
mass of oxygen = 16 grams
mass of chlorine = 35.5 grams
Therefore,
molar mass of c17h22clno4 = 17(12) + 22(1) + 35.5 + 14 + 4(16) = 339.5 grams

number of moles = mass / molar mass
number of moles = (23*10^-3) / (339.5)
number of moles = 6.77 * 10^-5 moles

number of atoms = number of moles * Avogadro's number
number of atoms = 6.77*10^-5 * 6.022*10^-23
number of atoms = 4.079 * 10^-27 atoms