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

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