Easy Chem Question Help

Can I get some help working this out please?

(Molecular formula = C16H13ClN2O)

How many molecules of diazepam are in 200 mg of the drug?

Note: C = 12 g mol-1; H = 1 g mol-1; Cl = 35.5 g mol-1; O = 16 g mol-1; N = 14 g mol-1

Express your answer in index form, rounding the first box to 1 d.p.

---- x10^--

Be very careful here; note that the question is asking for number of molecules.

Necessary prerequisite information:

The mole ([mol.]) is a unit referring to (6.02 [...])(10²³) elementary entities (molecules, ions, atoms, etc.).

Given information:

Mass (sample): 200 [mg], ≡ (200)(10^-3) [g]
Diazepam formula: C₁₆H₁₃ClN₂O

Calculations:

Molar Mass: (12)(16) + (1)(13) + (35.5) + (14)(2) + (16) = 284.5 [g][mol]^-1

∵

Moles [mol.] = (Mass [g])(Molar Mass [g][mol.]^-1)^-1,
Moles [mol.] = ((200)(10^{- 3}) [g])(284.5 [g][mol.]^-1)^-1 = (7.02)(10^-4) [mol.]

∵

One mole [mol.] = (6.02 [...])(10²³) molecules,
(7.02)(10^-4) moles [mol.] = (7.02)(10^-4)(6.02 [...])(10²³) = (4.23)(10²⁰) molecules = (4.2)(10²⁰) molecules, to one decimal place.